Battery load tester - low cost, high watts hybrid approach

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Battery load tester - low cost, high watts hybrid approach

Doug Weathers
I need to make sure my batteries are still in good health, so I went  
through the archives looking for information on battery testers.

I like this idea:


On Feb 22, 2007, at 6:59 PM, Bill Dube wrote:

> The most clever battery load tester (capacity test) I have ever  
> heard of was described to me by Steve Ciciora.
>
> This is limited to 12 volt (and perhaps 24 volt) batteries. You  
> could put two of your six volts in series, however.
>
> Buy an inverter that will handle the wattage of interest. These are  
> insanely cheap these days for what you get. Connect the inverter to  
> a 120 volt load that it will handle, like a 600 watt floodlight or a  
> space heater. Connect up an electric clock. Set it to 12 o'clock.
>
> Next, connect the fully-charged battery to the inverter. The  
> inverter will pull a constant wattage and then will automatically  
> shut off when it reaches its low-voltage threshold, typically 10.5  
> volts.
>
> The clock will shut off with the inverter so you will know the W-hr  
> capacity of the battery.
>
> You can use this to cycle up new batteries or to test older  
> batteries.
>
> Bill Dube'

Indeed very clever, but you need a high-watt inverter to do quick  
testing at high amps.  It may be a good value, but it's still more  
expensive than a coat hanger in a bucket.

Then there was this message:


On Feb 22, 2007, at 10:05 AM, Jeff Major wrote:

> John and all,
>
>  Here is a response I posted a while back for a guy wanting to test  
> 6 volt batteries.
>
>  "I never liked the "hot wire in water" method.  So I use large  
> power resistors.  MECI has some for cheap.
>
> http://www.meci.com/index.php
>
>  Look under resistors, under braking.  There is a 0.069 Ohm resistor  
> for $7.  It is probably rated about 1000 watts.  By the time you add  
> cable resistance, you will be close to 75 amps.  Who cares if it is  
> 69 or 81 amps?  Use the same set up on a known good battery and same  
> for the ones in question and compare times.  I use an old forklift  
> contactor, but you could get by without that.  I would use some type  
> of disconnect, like an Anderson, so you not fussing with a nut and  
> bolt to disconnect battery.  Things will get hot.  You'd also have  
> to fab up a support for the resistor.  Laying it on a piece of wood  
> will probably get smokey.  Put two resistors in parallel and it will  
> cut your test time down."


So how about combining the two methods?

Use a high-watt resistor (they're still available at MECI) and a  
contactor.  Connect it to the battery under test.

Power a 12v power supply, and the electro-mechanical clock, with a  
small cheap low-watt inverter with auto low-voltage shut-off.

Power the contactor with the 12v power supply.

Finally, power the inverter from the battery under test.

Reset the clock, turn on the inverter.  The 12v PS supplies 12vdc to  
the contactor, which closes and connects the braking resistor.

The battery drains to below the inverter's shut-off point, so the  
inverter shuts off.  This stops the clock and turns off the contactor,  
disconnecting the braking resistor from the battery.

Would this work?  Is this a good idea (i.e. worth doing)?

Thanks for any input,

Doug

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Re: Battery load tester - low cost, high watts hybrid approach

shred
For $35.00 or so Harbor Freight has a battery load tester with 125 amp load test. It reads out in digital voltage measurement. It will load the battery for about 10 seconds. At that point you will be able to see the finish voltage. IE: starting voltage 12.23vdc – finish voltage 10.4vdc. I usually run the traction pack down to about 50 – 60% SOC before testing. That way any suspect batteries will stand out with more catastrophic results. If I want more load sometimes I’ll turn the heater on while testing.
Neal
Doug Weathers wrote
I need to make sure my batteries are still in good health, so I went  
through the archives looking for information on battery testers.

I like this idea:


On Feb 22, 2007, at 6:59 PM, Bill Dube wrote:

> The most clever battery load tester (capacity test) I have ever  
> heard of was described to me by Steve Ciciora.
>
> This is limited to 12 volt (and perhaps 24 volt) batteries. You  
> could put two of your six volts in series, however.
>
> Buy an inverter that will handle the wattage of interest. These are  
> insanely cheap these days for what you get. Connect the inverter to  
> a 120 volt load that it will handle, like a 600 watt floodlight or a  
> space heater. Connect up an electric clock. Set it to 12 o'clock.
>
> Next, connect the fully-charged battery to the inverter. The  
> inverter will pull a constant wattage and then will automatically  
> shut off when it reaches its low-voltage threshold, typically 10.5  
> volts.
>
> The clock will shut off with the inverter so you will know the W-hr  
> capacity of the battery.
>
> You can use this to cycle up new batteries or to test older  
> batteries.
>
> Bill Dube'

Indeed very clever, but you need a high-watt inverter to do quick  
testing at high amps.  It may be a good value, but it's still more  
expensive than a coat hanger in a bucket.

Then there was this message:


On Feb 22, 2007, at 10:05 AM, Jeff Major wrote:

> John and all,
>
>  Here is a response I posted a while back for a guy wanting to test  
> 6 volt batteries.
>
>  "I never liked the "hot wire in water" method.  So I use large  
> power resistors.  MECI has some for cheap.
>
> http://www.meci.com/index.php
>
>  Look under resistors, under braking.  There is a 0.069 Ohm resistor  
> for $7.  It is probably rated about 1000 watts.  By the time you add  
> cable resistance, you will be close to 75 amps.  Who cares if it is  
> 69 or 81 amps?  Use the same set up on a known good battery and same  
> for the ones in question and compare times.  I use an old forklift  
> contactor, but you could get by without that.  I would use some type  
> of disconnect, like an Anderson, so you not fussing with a nut and  
> bolt to disconnect battery.  Things will get hot.  You'd also have  
> to fab up a support for the resistor.  Laying it on a piece of wood  
> will probably get smokey.  Put two resistors in parallel and it will  
> cut your test time down."


So how about combining the two methods?

Use a high-watt resistor (they're still available at MECI) and a  
contactor.  Connect it to the battery under test.

Power a 12v power supply, and the electro-mechanical clock, with a  
small cheap low-watt inverter with auto low-voltage shut-off.

Power the contactor with the 12v power supply.

Finally, power the inverter from the battery under test.

Reset the clock, turn on the inverter.  The 12v PS supplies 12vdc to  
the contactor, which closes and connects the braking resistor.

The battery drains to below the inverter's shut-off point, so the  
inverter shuts off.  This stops the clock and turns off the contactor,  
disconnecting the braking resistor from the battery.

Would this work?  Is this a good idea (i.e. worth doing)?

Thanks for any input,

Doug

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Re: Battery load tester - low cost, high watts hybrid approach

John Lussmyer
shred wrote:
> For $35.00 or so Harbor Freight has a battery load tester with 125 amp load
> test. It reads out in digital voltage measurement. It will load the battery
> for about 10 seconds. At that point you will be able to see the finish
> voltage. IE: starting voltage 12.23vdc – finish voltage 10.4vdc. I usually
> run the traction pack down to about 50 – 60% SOC before testing. That way
> any suspect batteries will stand out with more catastrophic results. If I
> want more load sometimes I’ll turn the heater on while testing.
>  

It had better NOT reach 10.4v after only 10 seconds!  If it does, it's a
dead battery anyway.

10 seconds just isn't enough time.

I'm STILL having "fun" trying to get a set of Optima Yellowtops that
actually work.
The last 2 I sent back had about a 40 minute Reserve Capacity (way lower
than the rated 120 min, and a lot lower than the expected 90 minute).  
The dealer has been stalling about replacing them, keeps telling me they
will ship "this" week.  He did tell me that he sent them back to the
factory, and that they tested good.  I then explained to him that the
CCA test that is usually done has nothing to do with Reserve Capacity.

I'm going to ask for a refund for those 2 batteries and just go pay a
local place more $$ to actually get them.
(It's been about 2 months this time!  Completely ridiculous)

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Re: Battery load tester - low cost, high watts hybrid approach

Tom Shay
In reply to this post by shred
The load tester described here is of limited value for testing EV batteries.
A
10-second test is good to determine if the battery can start an ICE.  Most
infernal combustion engines will usually start in under 10 seconds.

A fully charged yellow top Optima in good condition should be able to
deliver
125 amps for about 15 minutes.  Passing a 10-second test doesn't prove much.

----- Original Message -----
From: "shred" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, December 26, 2007 3:21 PM
Subject: Re: [EVDL] Battery load tester - low cost, high watts hybrid
approach


>
> For $35.00 or so Harbor Freight has a battery load tester with 125 amp
> load
> test. It reads out in digital voltage measurement. It will load the
> battery
> for about 10 seconds. At that point you will be able to see the finish
> voltage. IE: starting voltage 12.23vdc – finish voltage 10.4vdc. I usually
> run the traction pack down to about 50 – 60% SOC before testing. That way
> any suspect batteries will stand out with more catastrophic results. If I
> want more load sometimes I’ll turn the heater on while testing.
> Neal


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Re: Battery load tester - low cost, high watts hybrid approach

shred
In reply to this post by John Lussmyer
After draining the battery pack down until the pack voltage reads approximately 50% SOC the suspect batteries do sag to the low 10’s or worse.
I find that after my battery pack is at 50% SOC it falls on its face. It’s a 120v pack and a 400amp controller. If I hit the throttle and draw over 300 amps the pack voltage will drop into the 50’s. The batteries are Trojan AGM31 series & have always behaved this way. Trojan says they don’t recommend this battery for EV use anymore (thanks to me). They did a few tests that they hadn’t performed before, after I reported my problems and said they had the same results. Something about the “electrons not being able to transfer fast enough through the glass mat material after high current use etc… You’d be better off using FLA batteries for your application”.
As for the Optima batteries, I heard from a friend that Johnson Controls took over Optima and the quality was going downhill fast.


It had better NOT reach 10.4v after only 10 seconds!  If it does, it's a
dead battery anyway.

10 seconds just isn't enough time.

I'm STILL having "fun" trying to get a set of Optima Yellowtops that
actually work.
The last 2 I sent back had about a 40 minute Reserve Capacity (way lower
than the rated 120 min, and a lot lower than the expected 90 minute).  
The dealer has been stalling about replacing them, keeps telling me they
will ship "this" week.  He did tell me that he sent them back to the
factory, and that they tested good.  I then explained to him that the
CCA test that is usually done has nothing to do with Reserve Capacity.

I'm going to ask for a refund for those 2 batteries and just go pay a
local place more $$ to actually get them.
(It's been about 2 months this time!  Completely ridiculous)

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Re: Battery load tester - low cost, high watts hybrid approach

shred
In reply to this post by Tom Shay
Tom,
I agree but if you drain the pack down first by driving for 1/2 hour or so to 50% SOC then hit each battery with a load of 125 amps with the 1500w heater on, any weak batteries should show up a bigger voltage sag then the strong ones.
Neal
Tom Shay wrote
The load tester described here is of limited value for testing EV batteries.
A
10-second test is good to determine if the battery can start an ICE.  Most
infernal combustion engines will usually start in under 10 seconds.

A fully charged yellow top Optima in good condition should be able to
deliver
125 amps for about 15 minutes.  Passing a 10-second test doesn't prove much.

----- Original Message -----
From: "shred" <shred@scwi.us>
To: <ev@lists.sjsu.edu>
Sent: Wednesday, December 26, 2007 3:21 PM
Subject: Re: [EVDL] Battery load tester - low cost, high watts hybrid
approach


>
> For $35.00 or so Harbor Freight has a battery load tester with 125 amp
> load
> test. It reads out in digital voltage measurement. It will load the
> battery
> for about 10 seconds. At that point you will be able to see the finish
> voltage. IE: starting voltage 12.23vdc – finish voltage 10.4vdc. I usually
> run the traction pack down to about 50 – 60% SOC before testing. That way
> any suspect batteries will stand out with more catastrophic results. If I
> want more load sometimes I’ll turn the heater on while testing.
> Neal


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Re: Battery load tester - low cost, high watts hybrid approach

kenscircus
In reply to this post by John Lussmyer
Hey John,

I have been experiencing the exact same problem as you with Optima. Too
long a story to post and it would just be a re-hash.

Anyway, just though I would mention what I have been using as a load
tester. I sawed of a piece of scrap 1"X10" wood to fit the top of a 5
gallon paint bucket. Then I drilled it out to press fit 9 240 volt hot
water heater elements ($5 bucks each at Lowes). I only installed 5
elements which work out to 60 amps at 156 volts. Works great! with a
garden hose running in the bucket I run around the car logging voltages
until the low one(s) makes itself known. The running around the car
part also makes good exercise. :)   Eventually, I will get some pics up
on the Hot Juice website...

Ken



-----Original Message-----
From: John G. Lussmyer <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Wed, 26 Dec 2007 7:41 pm
Subject: Re: [EVDL] Battery load tester - low cost, high watts hybrid
approach



shred wrote:
> For $35.00 or so Harbor Freight has a battery load tester with 125
amp load
> test. It reads out in digital voltage measurement. It will load the
battery
> for about 10 seconds. At that point you will be able to see the finish
> voltage. IE: starting voltage 12.23vdc – finish voltage 10.4vdc. I
usually
> run the traction pack down to about 50 – 60% SOC before testing. That
way
> any suspect batteries will stand out with more catastrophic results.
If I
> want more load sometimes I’ll turn the heater on while testing.
>

It had better NOT reach 10.4v after only 10 seconds! If it does, it's a
dead battery anyway.

10 seconds just isn't enough time.

I'm STILL having "fun" trying to get a set of Optima Yellowtops that
actually work.
The last 2 I sent back had about a 40 minute Reserve Capacity (way
lower
than the rated 120 min, and a lot lower than the expected 90 minute).
The dealer has been stalling about replacing them, keeps telling me
they
will ship "this" week. He did tell me that he sent them back to the
factory, and that they tested good. I then explained to him that the
CCA test that is usually done has nothing to do with Reserve Capacity.

I'm going to ask for a refund for those 2 batteries and just go pay a
local place more $$ to actually get them.
(It's been about 2 months this time! Completely ridiculous)

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Opinions wanted on load tester idea

Doug Weathers
In reply to this post by Doug Weathers
I originally posted this in an overly wordy message with the subject
"Battery load tester - low cost, high watts hybrid approach".  Let me
try again, with more brevity.

I need to test a bunch of batteries that are not installed in a
vehicle.  I have an idea for a low cost, high watts battery load
tester.

Will this idea work, and is it worth pursuing?  Are there any Gotcha's
I should look out for?

Here's the idea:

Use a braking resistor from www.meci.com to load a single 12v battery.  
Also use that battery to power a cheap 12vdc-in/120vac-out inverter.  
The inverter then powers a mechanical clock/timer, and a 12vdc power
supply.  The 12v power supply activates a contactor that connects the
braking resistor to the battery.  When the battery gets too low, the
inverter shuts off and a) stops the clock and b) kills the 12v power
supply, which drops out the contactor, which disconnects the braking
resistor load, saving the battery from damage.

This lets you put a big load on a battery without needing to buy a big
inverter.

Of course you could use other loads, like a bucket full of water tank
heating elements, or some coat hangers, or a garage full of wire strung
across the walls.  I'm more concerned with evaluating the idea of using
a cheap inverter to switch the load in and out.

The cheap Harbor Freight load tester won't work for me because a) I
can't run the batteries down to 50% SOC before testing and b) I already
burned one of them up trying.

Thanks for your input!


--
Doug Weathers
Las Cruces, NM, USA
http://www.gdunge.com/

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Re: Opinions wanted on load tester idea

Morgan LaMoore
The main problem I see with this idea is that the clock won't be an
accurate measure of amp-hours or watt-hours.

As the battery discharges, the voltage drops. You could have two
batteries that both take the same amount of time to discharge, but one
sees more voltage sag. The one with less voltage sag will provide more
watt-hours and more amp-hours even though they will take the same time
to discharge.

Running the load from the inverter shouldn't have this problem; the
output of the inverter is a constant voltage at a constant resistance,
which equates to constant power. Thus, the inverter will draw an
(almost) constant power from the battery, so the clock will measure
time at constant watts, which is proportional to watt-hours.

That said, this shouldn't make a very big difference. If you're trying
to get very accurate readings and comparisons of your batteries, it
may not be good enough, but if you just want to check for dead
batteries, it should be more than adequate.

-Morgan LaMoore

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