Curtis 1238-6501 State of Charge

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Curtis 1238-6501 State of Charge

Electric Vehicle Discussion List mailing list
Hi Guys,

My 1238-6501 Curtis controller gives very different SOC % for similar
voltages.

For example I've recorded a pack voltage of 82.2 and had the Curtis show
22%, 31%, 43%.

The pack is made up of 25 Thundersky 160Ah batteries.

It's getting worse too. Now I'm getting the charger turning off at 92V
thinking the pack is fully charged and the Curtis is still at 25%.

Does anyone have experience of this and is there a way to get the Curtis to
recheck the pack voltage?

Many thanks,
Matthew

07966 806 727
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Re: Curtis 1238-6501 State of Charge

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On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
> Hi Guys,
>
> My 1238-6501 Curtis controller gives very different SOC % for similar
> voltages.
>
> For example I've recorded a pack voltage of 82.2 and had the Curtis show
> 22%, 31%, 43%.
>
> The pack is made up of 25 Thundersky 160Ah batteries.

With LFP cells, you can't accurately infer SOC from voltages in the
middle of the range.  The voltage/SOC curve is too flat.
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Re: Curtis 1238-6501 State of Charge

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I agree. Voltage on LFP cells is useless for determining the SOC.
The voltage is very constant except at near 100% SOC and at 0% SOC.
You really need information about the middle, and voltage doesn't give
any clue about that.

You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.

Bill D.

On 8/6/2017 7:00 PM, Willie via EV wrote:

>
>
> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>> Hi Guys,
>>
>> My 1238-6501 Curtis controller gives very different SOC % for similar
>> voltages.
>>
>> For example I've recorded a pack voltage of 82.2 and had the Curtis show
>> 22%, 31%, 43%.
>>
>> The pack is made up of 25 Thundersky 160Ah batteries.
>
> With LFP cells, you can't accurately infer SOC from voltages in the
> middle of the range.  The voltage/SOC curve is too flat.
> _______________________________________________
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> Read EVAngel's EV News at http://evdl.org/evln/
> Please discuss EV drag racing at NEDRA
> (http://groups.yahoo.com/group/NEDRA)
>
>

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Re: Curtis 1238-6501 State of Charge

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Thanks guys... but if the charger is turning off at a fixed voltage how do I get more power into the pack?


> On 7 Aug 2017, at 05:02, Bill Dube via EV <[hidden email]> wrote:
>
> I agree. Voltage on LFP cells is useless for determining the SOC.
> The voltage is very constant except at near 100% SOC and at 0% SOC.
> You really need information about the middle, and voltage doesn't give any clue about that.
>
> You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.
>
> Bill D.
>
>> On 8/6/2017 7:00 PM, Willie via EV wrote:
>>
>>
>>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>>> Hi Guys,
>>>
>>> My 1238-6501 Curtis controller gives very different SOC % for similar
>>> voltages.
>>>
>>> For example I've recorded a pack voltage of 82.2 and had the Curtis show
>>> 22%, 31%, 43%.
>>>
>>> The pack is made up of 25 Thundersky 160Ah batteries.
>>
>> With LFP cells, you can't accurately infer SOC from voltages in the middle of the range.  The voltage/SOC curve is too flat.
>> _______________________________________________
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>>
>>
>
> _______________________________________________
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Re: Curtis 1238-6501 State of Charge

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The surest way to destroy a pack of LFP cells is to fully charge them and
let then get hot as in over 100F.

Can you tell us the number of cells and their parallel series
configuration? Then specific recs can be made.

You may want to consider cutting of charging before fully charged state is
reached and never let them sit in a hot place if you have charged them to a
high SOC.

The problem is the positive electrode becomes very reactive with the
electrolyte when fully charged and temperature sets off a destructive
process.

I speak from experience, but also researching it. There is a long and
interesting video on YouTube of professor Jeff Dahn a long time battery's
researcher, discussing his. Try searching Jeff Dahn Waterloo lithium or
similar. It was a lecture he gave at Waterloo University. Dahn is an
electrochemistry at Dalhousie University in Novelty Scotia.

On Aug 7, 2017 3:00 AM, "Matthew Quitter via EV" <[hidden email]> wrote:

> Thanks guys... but if the charger is turning off at a fixed voltage how do
> I get more power into the pack?
>
>
> > On 7 Aug 2017, at 05:02, Bill Dube via EV <[hidden email]> wrote:
> >
> > I agree. Voltage on LFP cells is useless for determining the SOC.
> > The voltage is very constant except at near 100% SOC and at 0% SOC.
> > You really need information about the middle, and voltage doesn't give
> any clue about that.
> >
> > You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.
> >
> > Bill D.
> >
> >> On 8/6/2017 7:00 PM, Willie via EV wrote:
> >>
> >>
> >>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
> >>> Hi Guys,
> >>>
> >>> My 1238-6501 Curtis controller gives very different SOC % for similar
> >>> voltages.
> >>>
> >>> For example I've recorded a pack voltage of 82.2 and had the Curtis
> show
> >>> 22%, 31%, 43%.
> >>>
> >>> The pack is made up of 25 Thundersky 160Ah batteries.
> >>
> >> With LFP cells, you can't accurately infer SOC from voltages in the
> middle of the range.  The voltage/SOC curve is too flat.
> >> _______________________________________________
> >> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> >> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> >> Read EVAngel's EV News at http://evdl.org/evln/
> >> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/
> group/NEDRA)
> >>
> >>
> >
> > _______________________________________________
> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> > Read EVAngel's EV News at http://evdl.org/evln/
> > Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/
> group/NEDRA)
> >
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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> group/NEDRA)
>
>
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Re: Curtis 1238-6501 State of Charge

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Matthew Quitter via EV wrote:
> Thanks guys... but if the charger is turning off at a fixed voltage how do I get more power into the pack?

Like Bill Dube said; you measure amphours. Shut off the charger when you have
put back as many amphours as you took out (plus a little bit more to cover losses).

For example, the E-meter / Link-10 etc. has a switched output that can turn the
charger off. It can be configured to shut off when a) a certain voltage has been
reaches, b) the current has fallen below a set value, and c) at least 100% of
the amphours removed have been put back in.

--
Where ignorance is our master, there is no possibility of real peace.
        -- Dalai Lama
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: Curtis 1238-6501 State of Charge

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In reply to this post by Electric Vehicle Discussion List mailing list
Matthew Quitter via EV wrote:
> Thanks guys... but if the charger is turning off at a fixed voltage how do I get more power into the pack?

Like Bill Dube said; you measure amphours. Shut off the charger when you have
put back as many amphours as you took out (plus a little bit more to cover losses).

For example, the E-meter / Link-10 etc. has a switched output that can turn the
charger off. It can be configured to shut off when a) a certain voltage has been
reaches, b) the current has fallen below a set value, and c) at least 100% of
the amphours removed have been put back in.

--
Where ignorance is our master, there is no possibility of real peace.
        -- Dalai Lama
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: Curtis 1238-6501 State of Charge

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On 08/07/2017 01:53 AM, Matthew Quitter via EV wrote:
> Thanks guys... but if the charger is turning off at a fixed voltage how do I get more power into the pack?

The voltage rapidly rises as the cells near full charge.  Just as it
rapidly drops as they near empty.  The cells are supposed to survive up
to 4.2v but they are essentially fully charged at ~3.5v.  So, your
charger can be set to turn off at #cells x ~3.5 v.  Individual cells may
vary.  It is best to use a BMS to turn off charging when any cell gets
up above 3.5v.  AND turn off demand whenever a cell goes down to ~2.5v.
In the mid SOC range, cells should be 3.2-3.4 v.  You CAN tell when a
pack is near full charge by voltage.  You CAN tell when a pack is near
empty by voltage.  In the mid range, voltage is almost useless.  As we
noted.  An amp-hour counter is needed to keep track of SOC.  However,
IMHO, an amp-hour counter is a poor way to determine when to terminate
charging.

We are talking LFP cells here.  You really should educate yourself on
the topic before you ruin your pack.  It sounds like you may have a pack
set up by someone that believed in "bottom balancing".
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Re: Curtis 1238-6501 State of Charge

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Hi Michael,

Fortunately in the U.K. it never gets that hot!!!

I've got 25 160Ah Thundersky in series. I believe they're 3.3 nominal and online it says not to charge over 4V. But I'm never certain about that.

Thanks,
Matthew

Sent from my iPhone

> On 7 Aug 2017, at 12:59, Michael Ross <[hidden email]> wrote:
>
> The surest way to destroy a pack of LFP cells is to fully charge them and let then get hot as in over 100F.
>
> Can you tell us the number of cells and their parallel series configuration? Then specific recs can be made.
>
> You may want to consider cutting of charging before fully charged state is reached and never let them sit in a hot place if you have charged them to a high SOC.
>
> The problem is the positive electrode becomes very reactive with the electrolyte when fully charged and temperature sets off a destructive process.
>
> I speak from experience, but also researching it. There is a long and interesting video on YouTube of professor Jeff Dahn a long time battery's researcher, discussing his. Try searching Jeff Dahn Waterloo lithium or similar. It was a lecture he gave at Waterloo University. Dahn is an electrochemistry at Dalhousie University in Novelty Scotia.
>
>> On Aug 7, 2017 3:00 AM, "Matthew Quitter via EV" <[hidden email]> wrote:
>> Thanks guys... but if the charger is turning off at a fixed voltage how do I get more power into the pack?
>>
>>
>> > On 7 Aug 2017, at 05:02, Bill Dube via EV <[hidden email]> wrote:
>> >
>> > I agree. Voltage on LFP cells is useless for determining the SOC.
>> > The voltage is very constant except at near 100% SOC and at 0% SOC.
>> > You really need information about the middle, and voltage doesn't give any clue about that.
>> >
>> > You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.
>> >
>> > Bill D.
>> >
>> >> On 8/6/2017 7:00 PM, Willie via EV wrote:
>> >>
>> >>
>> >>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>> >>> Hi Guys,
>> >>>
>> >>> My 1238-6501 Curtis controller gives very different SOC % for similar
>> >>> voltages.
>> >>>
>> >>> For example I've recorded a pack voltage of 82.2 and had the Curtis show
>> >>> 22%, 31%, 43%.
>> >>>
>> >>> The pack is made up of 25 Thundersky 160Ah batteries.
>> >>
>> >> With LFP cells, you can't accurately infer SOC from voltages in the middle of the range.  The voltage/SOC curve is too flat.
>> >> _______________________________________________
>> >> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>> >> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
>> >> Read EVAngel's EV News at http://evdl.org/evln/
>> >> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
>> >>
>> >>
>> >
>> > _______________________________________________
>> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>> > http://lists.evdl.org/listinfo.cgi/ev-evdl.org
>> > Read EVAngel's EV News at http://evdl.org/evln/
>> > Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
>> >
>> _______________________________________________
>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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Re: Curtis 1238-6501 State of Charge

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In reply to this post by Electric Vehicle Discussion List mailing list
You have not given quite enough information about your system to fully
understand your issue.

However, to fully charge your 25 LFP cells to 100% SOC, your charger
should shut off at a voltage of a minimum of ~3.45 volts on all cells.
The full-charged pack voltage should be 87.5 volts, or a bit more.

3.6 to 3.8 volts on the highest cells is where your BMS should be set to
reduce the output of your charger. You should not be going over ~3.8
volts on any cell.

Your charger should be controlled by your BMS somehow, hopefully.

Like I said, we need a bit more information on your system to understand
exactly what your problem really is.

Bill D.

On 8/7/2017 12:53 AM, Matthew Quitter wrote:

> Thanks guys... but if the charger is turning off at a fixed voltage how do I get more power into the pack?
>
>
>> On 7 Aug 2017, at 05:02, Bill Dube via EV <[hidden email]> wrote:
>>
>> I agree. Voltage on LFP cells is useless for determining the SOC.
>> The voltage is very constant except at near 100% SOC and at 0% SOC.
>> You really need information about the middle, and voltage doesn't give any clue about that.
>>
>> You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.
>>
>> Bill D.
>>
>>> On 8/6/2017 7:00 PM, Willie via EV wrote:
>>>
>>>
>>>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>>>> Hi Guys,
>>>>
>>>> My 1238-6501 Curtis controller gives very different SOC % for similar
>>>> voltages.
>>>>
>>>> For example I've recorded a pack voltage of 82.2 and had the Curtis show
>>>> 22%, 31%, 43%.
>>>>
>>>> The pack is made up of 25 Thundersky 160Ah batteries.
>>> With LFP cells, you can't accurately infer SOC from voltages in the middle of the range.  The voltage/SOC curve is too flat.
>>> _______________________________________________
>>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>>> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
>>> Read EVAngel's EV News at http://evdl.org/evln/
>>> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
>>>
>>>
>> _______________________________________________
>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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>> Read EVAngel's EV News at http://evdl.org/evln/
>> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
>>

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Private note Re: Curtis 1238-6501 State of Charge

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In reply to this post by Electric Vehicle Discussion List mailing list
Michael,

Private note.

I would charge my A123 26650 cells fully, and heat them up to 70 Celsius
(160 F) and maintain that temperature all day in my drag bike. I did
this for _years_ will no issues. The cells would reach a peak
temperature of 90 to 100 Celsius (212 F) at the end of each run. We
would wait 20 minutes until they returned to 70 C, then recharge. We did
this routinely.

The calendar life is very much a function of temperature, and I was very
much chewing away at the calendar life by heating the cells. Not
"instant death" like you describe by any means.

The specific cell chemistry makes a huge difference as not all li-ion
cells, or even all LFP cells, have the same chemistry.

The formula 1 "KERS" cells are _designed_ to run continuously at 75
Celsius. They are LFP.

Bill D.


On 8/7/2017 5:59 AM, Michael Ross via EV wrote:

> The surest way to destroy a pack of LFP cells is to fully charge them and
> let then get hot as in over 100F.
>
> Can you tell us the number of cells and their parallel series
> configuration? Then specific recs can be made.
>
> You may want to consider cutting of charging before fully charged state is
> reached and never let them sit in a hot place if you have charged them to a
> high SOC.
>
> The problem is the positive electrode becomes very reactive with the
> electrolyte when fully charged and temperature sets off a destructive
> process.
>
> I speak from experience, but also researching it. There is a long and
> interesting video on YouTube of professor Jeff Dahn a long time battery's
> researcher, discussing his. Try searching Jeff Dahn Waterloo lithium or
> similar. It was a lecture he gave at Waterloo University. Dahn is an
> electrochemistry at Dalhousie University in Novelty Scotia.
>
> On Aug 7, 2017 3:00 AM, "Matthew Quitter via EV" <[hidden email]> wrote:
>
>> Thanks guys... but if the charger is turning off at a fixed voltage how do
>> I get more power into the pack?
>>
>>
>>> On 7 Aug 2017, at 05:02, Bill Dube via EV <[hidden email]> wrote:
>>>
>>> I agree. Voltage on LFP cells is useless for determining the SOC.
>>> The voltage is very constant except at near 100% SOC and at 0% SOC.
>>> You really need information about the middle, and voltage doesn't give
>> any clue about that.
>>> You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.
>>>
>>> Bill D.
>>>
>>>> On 8/6/2017 7:00 PM, Willie via EV wrote:
>>>>
>>>>
>>>>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>>>>> Hi Guys,
>>>>>
>>>>> My 1238-6501 Curtis controller gives very different SOC % for similar
>>>>> voltages.
>>>>>
>>>>> For example I've recorded a pack voltage of 82.2 and had the Curtis
>> show
>>>>> 22%, 31%, 43%.
>>>>>
>>>>> The pack is made up of 25 Thundersky 160Ah batteries.
>>>> With LFP cells, you can't accurately infer SOC from voltages in the
>> middle of the range.  The voltage/SOC curve is too flat.
>>>> _______________________________________________
>>>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>>>> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
>>>> Read EVAngel's EV News at http://evdl.org/evln/
>>>> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/
>> group/NEDRA)
>>>>
>>> _______________________________________________
>>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>>> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
>>> Read EVAngel's EV News at http://evdl.org/evln/
>>> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/
>> group/NEDRA)
>> _______________________________________________
>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
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>> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/
>> group/NEDRA)
>>
>>
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Re: Curtis 1238-6501 State of Charge

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Thanks Bill, sorry I'll try and give you more information.

I'm using a Zivan NG3 charger and don't have a BMS at the moment, just a
bunch of QNBBM cell balancers.

Previously I stopped the charge manually when the Curtis was saying 100%.
The Zivan also displays a charging progress and it would also be at 100%.
But lately the Curtis is saying 30% when the Zivan is showing 80% complete
and some of the cells are starting to jump up to 4V during that phase of
the charge. Whenever a cell goes over 4V I've been stopping the charge and
allowing the cell balancers to even out the pack again.

Is there anything other information I should be providing?

Thanks for your help.

Matthew



It all came out of a working car and has been fine until recently when the
pack

07966 806 727


On 7 August 2017 at 15:13, Bill Dube via EV <[hidden email]> wrote:

> You have not given quite enough information about your system to fully
> understand your issue.
>
> However, to fully charge your 25 LFP cells to 100% SOC, your charger
> should shut off at a voltage of a minimum of ~3.45 volts on all cells.
> The full-charged pack voltage should be 87.5 volts, or a bit more.
>
> 3.6 to 3.8 volts on the highest cells is where your BMS should be set to
> reduce the output of your charger. You should not be going over ~3.8 volts
> on any cell.
>
> Your charger should be controlled by your BMS somehow, hopefully.
>
> Like I said, we need a bit more information on your system to understand
> exactly what your problem really is.
>
> Bill D.
>
>
> On 8/7/2017 12:53 AM, Matthew Quitter wrote:
>
>> Thanks guys... but if the charger is turning off at a fixed voltage how
>> do I get more power into the pack?
>>
>>
>> On 7 Aug 2017, at 05:02, Bill Dube via EV <[hidden email]> wrote:
>>>
>>> I agree. Voltage on LFP cells is useless for determining the SOC.
>>> The voltage is very constant except at near 100% SOC and at 0% SOC.
>>> You really need information about the middle, and voltage doesn't give
>>> any clue about that.
>>>
>>> You need to count the amp-hours, like with an E-meter or a Cycle-Analyst.
>>>
>>> Bill D.
>>>
>>> On 8/6/2017 7:00 PM, Willie via EV wrote:
>>>>
>>>>
>>>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>>>>> Hi Guys,
>>>>>
>>>>> My 1238-6501 Curtis controller gives very different SOC % for similar
>>>>> voltages.
>>>>>
>>>>> For example I've recorded a pack voltage of 82.2 and had the Curtis
>>>>> show
>>>>> 22%, 31%, 43%.
>>>>>
>>>>> The pack is made up of 25 Thundersky 160Ah batteries.
>>>>>
>>>> With LFP cells, you can't accurately infer SOC from voltages in the
>>>> middle of the range.  The voltage/SOC curve is too flat.
>>>> _______________________________________________
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>>>> /NEDRA)
>>>>
>>>>
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>>>
>>>
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Re: Curtis 1238-6501 State of Charge

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On 08/07/2017 10:58 AM, Matthew Quitter via EV wrote:

> Thanks Bill, sorry I'll try and give you more information.
>
> I'm using a Zivan NG3 charger and don't have a BMS at the moment, just a
> bunch of QNBBM cell balancers.
>
> Previously I stopped the charge manually when the Curtis was saying 100%.
> The Zivan also displays a charging progress and it would also be at 100%.
> But lately the Curtis is saying 30% when the Zivan is showing 80% complete
> and some of the cells are starting to jump up to 4V during that phase of
> the charge. Whenever a cell goes over 4V I've been stopping the charge and
> allowing the cell balancers to even out the pack again.

It is good to hear you have balancers.  You seem to describe a pack that
is not well balanced.  It is a new pack?  Never before balanced?  Once
you get it balanced your troubles will almost certainly diminish and the
balancers will tend to improve things with each full charge.  One
balancing strategy would be to contrive to charge at a low rate once so
that your balancers can keep up.  A charger that charges at a lower rate
than the balancers can pass.  As Lee Hart might suggest, you might use
some combination of incandescent light bulbs for current limiting.
Another strategy would be to get one or more single cell chargers and
charge all cells with it/them sequentially.

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Re: Curtis 1238-6501 State of Charge

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On 08/07/2017 10:58 AM, Matthew Quitter via EV wrote:
> Thanks Bill, sorry I'll try and give you more information.

I don't find a Quitter on http://evalbum.com
If you are there, you should tell us how to find you.  If not, you
should consider making an EVAlbum page.

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Re: Curtis 1238-6501 State of Charge

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Hey Willie,

I've used that website so many times to look at other conversions and never
once thought of putting myself up there. Will do!

Thanks,
Matthew

07966 806 727


On 7 August 2017 at 17:14, Willie via EV <[hidden email]> wrote:

>
>
> On 08/07/2017 10:58 AM, Matthew Quitter via EV wrote:
>
>> Thanks Bill, sorry I'll try and give you more information.
>>
>
> I don't find a Quitter on http://evalbum.com
> If you are there, you should tell us how to find you.  If not, you should
> consider making an EVAlbum page.
>
>
> _______________________________________________
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> /NEDRA)
>
>
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Re: Curtis 1238-6501 State of Charge

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Sure you can. Voltage is the only way to discern SOC.
You just can't measure accurately under load. You have to measure open circuit voltage.
www.mdpi.com/1996-1073/9/11/900/pdf



      From: Willie via EV <[hidden email]>
 To: Matthew Quitter via EV <[hidden email]>
 Sent: Sunday, August 6, 2017 9:13 PM
 Subject: Re: [EVDL] Curtis 1238-6501 State of Charge
   


On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
> Hi Guys,
>
> My 1238-6501 Curtis controller gives very different SOC % for similar
> voltages.
>
> For example I've recorded a pack voltage of 82.2 and had the Curtis show
> 22%, 31%, 43%.
>
> The pack is made up of 25 Thundersky 160Ah batteries.

With LFP cells, you can't accurately infer SOC from voltages in the
middle of the range.  The voltage/SOC curve is too flat.
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Re: Curtis 1238-6501 State of Charge

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Looking at the instructions for the QNBBM battery balancers, they appear
to be able to balance the battery pack and handle a continuous current
of 6 amps. It that correct? Do I have the right model?

If I have the correct model, and they can take 6 amps, then you should
be able to set your charger up to balance your pack. You need to be able to:

1) Set your charger to charge at 6 amps or less
2) Set your charger to a maximum voltage of 90 volts or so.
3) Put the whole thing on a timer.

Basically, to balance your pack, you should run your charger at some
current below the 6 amps that the QNBBM balancers will handle. (or make
some sort of low current charger for balancing.) Run this low current
through the pack until all the cells are above 3.45 to 3.5 volts. Be
careful _never_ to allow any cells to go above ~3.9 volts. You are done!

You really don't want this set up to run unattended. You likely want to
put some sort of wind up timer on the circuit, because some day you will
run it and forget that it is running.
Like this one:
https://www.mcmaster.com/#7014k9/=18ud5en

Bill D.



On 8/7/2017 9:58 AM, Matthew Quitter via EV wrote:

> Thanks Bill, sorry I'll try and give you more information.
>
> I'm using a Zivan NG3 charger and don't have a BMS at the moment, just a
> bunch of QNBBM cell balancers.
>
> Previously I stopped the charge manually when the Curtis was saying 100%.
> The Zivan also displays a charging progress and it would also be at 100%.
> But lately the Curtis is saying 30% when the Zivan is showing 80% complete
> and some of the cells are starting to jump up to 4V during that phase of
> the charge. Whenever a cell goes over 4V I've been stopping the charge and
> allowing the cell balancers to even out the pack again.
>
> Is there anything other information I should be providing?
>
> Thanks for your help.
>
> Matthew
>
>

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Re: Curtis 1238-6501 State of Charge

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In LFP, temperature influences voltage more than SOC in the region of
20% to 80% SOC. The voltage changes just a tiny amount between 20% and
80% SOC.

Basically, if the voltage changes it is more likely to be due to a
change in temperature, than a change in SOC.

Indeed, you could measure the temperature of each cell, along with the
voltage, to tease out the SOC, but you need the average internal
temperature of the cell, rather than the external temperature of the
cell, and you need a very accurate measure of voltage. It is way simpler
and cheaper to count amps.


On 8/7/2017 2:31 PM, paul dove via EV wrote:

> Sure you can. Voltage is the only way to discern SOC.
> You just can't measure accurately under load. You have to measure open circuit voltage.
> www.mdpi.com/1996-1073/9/11/900/pdf
>
>
>
>        From: Willie via EV <[hidden email]>
>   To: Matthew Quitter via EV <[hidden email]>
>   Sent: Sunday, August 6, 2017 9:13 PM
>   Subject: Re: [EVDL] Curtis 1238-6501 State of Charge
>    
>
>
> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>> Hi Guys,
>>
>> My 1238-6501 Curtis controller gives very different SOC % for similar
>> voltages.
>>
>> For example I've recorded a pack voltage of 82.2 and had the Curtis show
>> 22%, 31%, 43%.
>>
>> The pack is made up of 25 Thundersky 160Ah batteries.
> With LFP cells, you can't accurately infer SOC from voltages in the
> middle of the range.  The voltage/SOC curve is too flat.
> _______________________________________________
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>
>
>
>    
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Re: Curtis 1238-6501 State of Charge

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Hi Guys,

Thanks for all the feedback, really interesting.

I have a 10 year old battery pack, I got it second hand out of an old
conversion.

The balancers do a great job of keeping the pack balanced, I think they can
move around 10A. Most of the time they can keep the charge in control, it's
only in the last 20% where I guess the charger is doing constant voltage
and I guess is pushing more current than the balancers can move. Or the
batteries are reaching their limit and no amount of balancing is going to
add more charge to certain cells.

Basically my pack has a couple of outlier cells that charge really slowly
(as in their voltage doesn't change) and a couple of cells that charge
really quickly (the voltage rises up and over 4V quite quickly). I've found
that looking at the cell voltages gives a fairly accurate representation of
the SOC. I've logged each cell every few hours, particularly after a charge
or a drive, over a week or two and everything was fine until recently. I
measure down to the millivolt. Is that accurate enough? And our temperature
here is so stable, particularly in the underground garage where I keep the
car that I can't imagine the internal temp of the battery is really that
different to ambient but I don't know much about all this. Will go and do
some research.

It's like the Curtis SOC has missed a chunk of Ah going into the pack. I
guess I'll have to draw the pack down using a load to get the charger and
the Curtis on the same wavelength again. I looked at single cell
charger/discharger but the ones I saw do max 2A and the maths of 25 160Ah
cells meant I was facing two months of slowly discharging cells!

I've gotten a lot conflicting advice about the max charge voltage of a
Thundersky cell. Bill said to not let them go above 3.8V while the
Thundersky page -
http://www.thunderstruck-ev.com/Manuals/Thundersky%20Product%20Manual.pdf -
says 4.25V. I tend to stop the charging when cells get over 4V. Is that
causing damage to the battery?

I was planning on building my own charge monitoring system using an arduino
to monitor individual cell voltages and if any one cell goes above say 3.8V
then shut off charging for a period of time to let the balancers work. And
then shut off the entire charge once the pack reached a fixed voltage - say
88V. But you guys are saying that shutting of charge at 88V would not give
me an accurate reflection of a fully charged pack. I'll look at the Ah
meters you linked to.

Many thanks,
Matthew

07966 806 727


On 8 August 2017 at 08:00, Bill Dube via EV <[hidden email]> wrote:

> In LFP, temperature influences voltage more than SOC in the region of 20%
> to 80% SOC. The voltage changes just a tiny amount between 20% and 80% SOC.
>
> Basically, if the voltage changes it is more likely to be due to a change
> in temperature, than a change in SOC.
>
> Indeed, you could measure the temperature of each cell, along with the
> voltage, to tease out the SOC, but you need the average internal
> temperature of the cell, rather than the external temperature of the cell,
> and you need a very accurate measure of voltage. It is way simpler and
> cheaper to count amps.
>
>
>
> On 8/7/2017 2:31 PM, paul dove via EV wrote:
>
>> Sure you can. Voltage is the only way to discern SOC.
>> You just can't measure accurately under load. You have to measure open
>> circuit voltage.
>> www.mdpi.com/1996-1073/9/11/900/pdf
>>
>>
>>
>>        From: Willie via EV <[hidden email]>
>>   To: Matthew Quitter via EV <[hidden email]>
>>   Sent: Sunday, August 6, 2017 9:13 PM
>>   Subject: Re: [EVDL] Curtis 1238-6501 State of Charge
>>
>>
>> On 08/06/2017 07:38 PM, Matthew Quitter via EV wrote:
>>
>>> Hi Guys,
>>>
>>> My 1238-6501 Curtis controller gives very different SOC % for similar
>>> voltages.
>>>
>>> For example I've recorded a pack voltage of 82.2 and had the Curtis show
>>> 22%, 31%, 43%.
>>>
>>> The pack is made up of 25 Thundersky 160Ah batteries.
>>>
>> With LFP cells, you can't accurately infer SOC from voltages in the
>> middle of the range.  The voltage/SOC curve is too flat.
>> _______________________________________________
>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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>> Read EVAngel's EV News at http://evdl.org/evln/
>> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group
>> /NEDRA)
>>
>>
>>
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Re: Curtis 1238-6501 State of Charge

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paul dove via EV wrote:
> Sure you can. Voltage is the only way to discern SOC.
> You just can't measure accurately under load. You have to measure open circuit voltage.
> www.mdpi.com/1996-1073/9/11/900/pdf

This paper mainly discusses the higher-voltage Li-Ion cells, which have a larger
voltage change between full and empty.

For the LiFePO3 cells being discussed here, the voltage change is much smaller.
As Bill says, the change is so small that it can't be reliably measured outside
of laboratory conditions and precisions instruments. Other factors, such as age,
temperature, manufacturing variations, and the accuracy of the equipment play a
larger factor.

--
Where ignorance is our master, there is no possibility of real peace.
        -- Dalai Lama
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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