rheostat type

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rheostat type

BFratto
What type of rheostat would I look for so I can turn down my Zivan 115 VAC
charger?

even 50 foot of cord didn't prevent tripping the breaker at a friends
house.

a rheostat is the right product?

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Re: rheostat type

Lee Hart
[hidden email] wrote:
> What type of rheostat would I look for so I can turn down my Zivan 115 VAC
> charger?
>
> even 50 foot of cord didn't prevent tripping the breaker at a friends
> house.
>
> a rheostat is the right product?

The Zivan is a "smart" charger; if you lower the input AC voltage with a
rheostat or variac, the Zivan will just *increase* the AX current it
draws in an effort to maintain output current.

There are a couple things you can do to keep it from blowing AC
breakers. First, you can turn down the *output* current. I don't know
what model you have or if such a control is available, but look for it.

Second, you can add a big AC rated capacitor in parallel with the AC
input to the charger. It must NOT be an electrolytic or motor starting
type! The correct part is a metal can type, usually oil-filled, and
built for motor *run* capacitors and with a voltage rating of 300vac or
more. This slightly improves its power factor. The correct capacitance
needs to be chosen to minimize the input AC current. You need an AC
ammeter on the input to do this. It will probably take 10-50 microfarads.

Third, you can add a resistor in series with the charger's output to
limit the current. This will be a big resistor, and it will get hot!
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Re: rheostat type

Morgan LaMoore
In reply to this post by BFratto
Actually, with a "smart" charger like a Zivan, adding a rheostat or
extension cord will probably make it take more current, not less.

The Zivan uses a "switched-mode power supply"; it tries to put a
constant current through the battery in the bulk charge. The more
output power it gives, the more input power it needs.

 If you add a rheostat between the charger and wall, it has a lower
input voltage, so it tries to take more input current to get the same
power so it can still charge the battery at the programmed rate.

If you add the rheostat between the charger and battery, it still puts
the same programmed current through the battery, but because of the
rheostat, the output voltage is higher (for bulk phase, at least).
That means that the output power is higher, so the input current must
be higher to make up for it. Again, this increase in input current
makes tripping breakers even more of a problem.

Adding a rheostat to a smart charger won't make it take less current
from the wall. Instead, look for an adjustable current limit in your
charger's manual. There may be something as simple as a potentiometer
on the charger that you can adjust, or it may require re-programming
your charger, which Zivan may not let you do.

-Morgan LaMoore

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Re: rheostat type

gottdi
If it's an old house with old wiring it may not be able to handle the  
load.

Pete


On Nov 26, 2007, at 10:37 AM, Morgan LaMoore wrote:

> Actually, with a "smart" charger like a Zivan, adding a rheostat or
> extension cord will probably make it take more current, not less.
>
> The Zivan uses a "switched-mode power supply"; it tries to put a
> constant current through the battery in the bulk charge. The more
> output power it gives, the more input power it needs.
>
>  If you add a rheostat between the charger and wall, it has a lower
> input voltage, so it tries to take more input current to get the same
> power so it can still charge the battery at the programmed rate.
>
> If you add the rheostat between the charger and battery, it still puts
> the same programmed current through the battery, but because of the
> rheostat, the output voltage is higher (for bulk phase, at least).
> That means that the output power is higher, so the input current must
> be higher to make up for it. Again, this increase in input current
> makes tripping breakers even more of a problem.
>
> Adding a rheostat to a smart charger won't make it take less current
> from the wall. Instead, look for an adjustable current limit in your
> charger's manual. There may be something as simple as a potentiometer
> on the charger that you can adjust, or it may require re-programming
> your charger, which Zivan may not let you do.
>
> -Morgan LaMoore
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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No need to wait any longer. You can now buy one off the shelf. You can still build one too.
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Re: rheostat type

Roland Wiench
In reply to this post by BFratto
A rheostat would have to be too large and may cost more then the battery
charger.  If you are plug into a 20 amp 120 volt receptacle circuit then the
smallest one would be a 20A x 120 V = 2400 watts at a 20 amp rating minimum.
Normally if you are pulling all of 20 amps, then a unit should be at least
rated for 125% over the load you are pulling  or 20 x 1.25 = 25 amp circuit
breaker.

It is best to stay below the rating of a 20 amp circuit to a maximum of 16
amps.

A transformer variac which can be plug into a 120v 20 amp receptacle circuit
which the smaller bench type unit is rated for 0 to 140 volts at a maximum
of 18 amps would be better than a large rheostat that you are burning up the
power you are not using.

See www.surplussales.com for source of supply on these type of items.

Roland


----- Original Message -----
From: <[hidden email]>
To: <[hidden email]>
Sent: Monday, November 26, 2007 10:49 AM
Subject: [EVDL] rheostat type


> What type of rheostat would I look for so I can turn down my Zivan 115 VAC
> charger?
>
> even 50 foot of cord didn't prevent tripping the breaker at a friends
> house.
>
> a rheostat is the right product?
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Re: rheostat type

Lee Hart
Roland Wiench wrote:
> A rheostat would have to be too large and may cost more than the
> battery charger. If you are plug into a 20 amp 120 volt receptacle
> circuit then the smallest one would be a 20A x 120 V = 2400 watts
> at a 20 amp rating minimum.

It's not quite that bad.

With a simple non-regulated charger, you can put a rheostat in series
with either the AC input or DC output. With a "smart" charger that tries
to regulate its output, the rheostat has to be in the output or the
charger will try to cancel out the resistance.

The rheostat doesn't have to drop the entire voltage -- normally just a
few volts will do. If it's a 20 amp charger, 3 volts x 20 amps is 60
watts. Big, but not excessively so.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Re: rheostat type

John Lussmyer
Lee Hart wrote:

> It's not quite that bad.
>
> With a simple non-regulated charger, you can put a rheostat in series
> with either the AC input or DC output. With a "smart" charger that tries
> to regulate its output, the rheostat has to be in the output or the
> charger will try to cancel out the resistance.
>
> The rheostat doesn't have to drop the entire voltage -- normally just a
> few volts will do. If it's a 20 amp charger, 3 volts x 20 amps is 60
> watts. Big, but not excessively so.
>
>  

Yeah, but with a smart charger, won't that accomplish exactly nothing?
The charger will still put out XXX volts at YY Amps.  Just some of it
goes through the resistor and produces heat, instead of into the
batteries to produce charge.
So the charger will still pull too much out of the outlet and pop the
breaker.  (Which Zivans are very good at.)

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Re: rheostat type

Lee Hart
In reply to this post by BFratto
>> With a "smart" charger that tries to regulate its output, the rheostat
>> has to be in the output or the charger will try to cancel out the
>> resistance.

From: John G. Lussmyer
> With a smart charger, won't that accomplish exactly nothing?
> The charger will still put out X volts at Y Amps.  Just some of
> it goes through the resistor and produces heat, instead of into
> the batteries to produce charge. So the charger will still pull
> too much out of the outlet and pop the breaker. (Which Zivans
> are very good at.)

The resistor needs to be big enough to defeat the charger's constant current mode.

For example, say the charger is programmed for 145v and 20 amps (14.5v per 12v battery for 10 batteries). The actual battery voltage is 12.5 volts charging at 20 amps. 145v at 20a is too much for your 120vac 15amp outlet, so the breaker trips.

Let's say we want to reduce it to 10 amps. The charger will voltage limit (regulate voltage, and stop regulating current) at 145v. The batteries will be at 125v. So the resistor needs to drop th evoltage difference at 10 amps. R = 20v / 10a = 2 ohms. P = 20v x 10a = 200 watts.

This ignores the Zivan's power factor and efficiency, but you get the idea.

--
"Excellence does not require perfection." -- Henry James
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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Re: rheostat type

David Nelson-5
In reply to this post by Lee Hart
On Nov 26, 2007 10:32 AM, Lee Hart <[hidden email]> wrote:
> [hidden email] wrote:
> > What type of rheostat would I look for so I can turn down my Zivan 115 VAC
> > charger?
[[snip]]
>
> There are a couple things you can do to keep it from blowing AC
> breakers. First, you can turn down the *output* current. I don't know
> what model you have or if such a control is available, but look for it.

Tim K, at http://www.914ev.blogspot.com/, had Zivan put in a toggle
switch so that he could switch between high and low current. I believe
he is an EE so he might be able to tell you what they did to modify
it.

--
David D. Nelson

http://www.austinev.org/evalbum/1328

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