[EVDL] Resistance of a coat hanger and calibrating a Sears charger

I use a piece of 1/8 inch steel welding rod, I think 30" across a single
CALB battery is 95 amps. That's at about 3 volts. A 30" piece of 1/16"
steel welding rod at 30 inches is about 30 amps on a CALB. You need to
multiply times 4 for a 12 volt battery. I wound them both into 3" spirals
about 4 inches long. They fit nicely into a round plastic juice pitcher,
just make sure it stays full of water. Works really nicely.

Sincerely,
Mark Grasser


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Christopher Zach
Sent: Saturday, February 26, 2011 3:23 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] Resistance of a coat hanger and calibrating a Sears charger

Quick question since I can't find it on google: Does anyone know what
the resistance of a coat hanger wire in a 5 gallon bucket of water is?

I'm working on testing these old hawkers in my driveway (EP26ah, sitting
for 3 years or so, they were 5 years old before that, in other words
probably fine) and I have been working them in strings of 7.

Connections between batteries is 10g wire, I am using my large Sears
charger (up to 250a charge), and a coat hanger in water connected to
jumper cables for discharge.

The batteries will happily smoke the water, but my meter only shows 0
ohms when I check at the jumper cables. I think it's pulling more than
100a since the spark on disconnect is bigger than the spark on
disconnect with the charger, but it would be interesting to know how much.

The batteries will also happily peg the charger's meter to 250 using car
start mode on this charger (note, it's a big transformer charger, wheels
and all that, the biggest Sears one, not a little toy one) with a
voltage of 12.5v @ "250a". Which I kind of doubt a bit since:

12v*250a=2,700 watts. Using my Watts Up meter I see it pulling 16a from
120v, so it's either over-unity or optimistic (maybe 100a)

However charging at 50a, the meter on the charger says about 50a, with a
voltage at battery of 13.0. The Watts up meter shows [email protected] 1080
watts. Which would make the battery side 650 watts or an efficiency of
about 60%. Is that in line with a transformer based charger?

Thanks!
Chris

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Hello Chris,

I made my own battery load meter that can test 2 to 12 volt deep cell
batteries at a 75 amp load. I first had it set for 300 amps when I first
test my first battery pack back in 76 which was the wrong setting for a deep
cycle battery. The higher ampere is fine to find a bad and/or shorted cell,
but not good to see how long a battery will discharge at about the same rate
that a EV discharges the battery.

Found this out when I call battery tech and they said do not test these
types of battery like a cranking amp battery. They said to go to a auto
parts store and some of them have a 75 amp load tester that are design for a
deep cycle battery. I did that, and look at one that ran about $50.00 at
the time which was a lot cheaper than the one I made with consist of the
following parts:

1. Stainless steel high temperature (1000 F.) welding wire that comes in
sticks of 36 inches long. I took my ohm meter with me and select a welding
wires that read less than one ohm. Some of them read over 1 ohm which is
too much. I needed at least 6 to 6.5 volt / 75 amps = 0.08 to 0.08 ohms.

2. Insulated large setscrew terminal block or sometimes call a power block
that size for No. 6 to 1 AWG stranded copper welding wire.

3. A 6 volt auto starter continuous rated contactor which is design to mount
on the firewall of the older vehicles rated at 100 amps which you can still
get from some auto parts store.

4. A 0 to 15 volt auto volt meter

5. A 0 to 300 amp meter (could have use a 100 amp meter-anything over 60
amps require a shunt)

7. A on-off toggle switch to turn on the contactor coil.

8. A enclosure with handle to contain all of the above items. I made my out
of 0.125 inch thick aluminum plates fasten together in the corners by 1/2
inch aluminum angles. A series of ventilation holes was drill on the top and
on the bottom of the back plate for ventilation of the load bank. Do not
need water cooling.

9. Two cable bushings to exit the test leads which was a No. 6 AWG copper
stranded welding wire that are connected to 100 amp heavy duty battery
clamps. (Had double up No 6 wire to a heavy duty 500 amp battery clamps
when I thought I need a 300 amp load tester.)

Theory of Operation:

1. Make sure the ON-OFF toggle switch is in the off position before
connecting and disconnected the cable leads or you could arc the battery
clamps. Unlike a cranking amp tester, this switch is normally a momentary
type you hold for about 15 seconds.

The formula for checking out a deep cycle battery for a certain amount of
time is:

The Reserved Minutes at the listed discharge ampere for a
certain amount of time.

Lets say the reserved minutes is 150 minutes at 75 amps, then:

150 minutes / 60 = 2.5 hours

2.5 hours x 75 amps = 187.5 ampere hour at 100% DOD.

Usable AH may be 187.5/2 = 93.75 ah in 2.5/2 = 1.25 hours
which is 50% DOD or 6.05 volts for a 6 volt or 12.1 V for
a 12 volt battery at rest.

If you find your battery is discharge to 25% DOD in 1.25/2 =
62.5 minutes and the voltage is reading about 6.22 v or
12.44 v then the battery is consider good.

You will have to download the specifications for your battery what the State
Of Charge (SOC) is at the No Load Voltage so you can compare those two data
points as you test the battery. Sometimes you can just do a very short
discharge load to analyze the battery.

Roland








----- Original Message -----
From: "Christopher Zach" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Saturday, February 26, 2011 12:23 PM
Subject: [EVDL] Resistance of a coat hanger and calibrating a Sears charger


> Quick question since I can't find it on google: Does anyone know what
> the resistance of a coat hanger wire in a 5 gallon bucket of water is?
>
> I'm working on testing these old hawkers in my driveway (EP26ah, sitting
> for 3 years or so, they were 5 years old before that, in other words
> probably fine) and I have been working them in strings of 7.
>
> Connections between batteries is 10g wire, I am using my large Sears
> charger (up to 250a charge), and a coat hanger in water connected to
> jumper cables for discharge.
>
> The batteries will happily smoke the water, but my meter only shows 0
> ohms when I check at the jumper cables. I think it's pulling more than
> 100a since the spark on disconnect is bigger than the spark on
> disconnect with the charger, but it would be interesting to know how much.
>
> The batteries will also happily peg the charger's meter to 250 using car
> start mode on this charger (note, it's a big transformer charger, wheels
> and all that, the biggest Sears one, not a little toy one) with a
> voltage of 12.5v @ "250a". Which I kind of doubt a bit since:
>
> 12v*250a=2,700 watts. Using my Watts Up meter I see it pulling 16a from
> 120v, so it's either over-unity or optimistic (maybe 100a)
>
> However charging at 50a, the meter on the charger says about 50a, with a
> voltage at battery of 13.0. The Watts up meter shows [email protected] 1080
> watts. Which would make the battery side 650 watts or an efficiency of
> about 60%. Is that in line with a transformer based charger?
>
> Thanks!
> Chris
>
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It might be able to approximate this from the data you have given:

Like you, I would believe the Watts up meter much more than the charger's
meter. 16A at 120V = 1920W. Personally, I would expect the charger
efficiency to be higher than 60%. I would think somewhere around 80-85%. (I
would be very wary of the built-in amp gauge on any charger.) If we're
being generous, that would put the output of the charger at 1600 W (85%
efficiency) or about 130A if the 12.5V reading is correct. If we trust the
voltage on the charger is correct at 12.5V, we can calculate the resistance
of the wire and water. (It might be worth checking the voltage with a
volt-ohm meter to find out if the charger has that reading right.)

V=IR. V=12.5, I=130A, R=
12.5V=~130A * R

R = ~1/10 ohm.

You should be able to measure that on a meter, but I bet the resistance is
changing with that kind of current as the wire heats up.

If you could measure the voltage and current through the wire more
precisely, you could nail the number closer. Probably still in the range of
1/10 ohm, though.

Or, since you really wanted the amperage, you could just go with the
calculation based on charger efficiency. If your car has a high-current
ammeter with shunt, you might be able to pull that out and read the current
almost directly on the ammeter.

Mike

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Christopher Zach
Sent: Saturday, February 26, 2011 1:23 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] Resistance of a coat hanger and calibrating a Sears charger

Quick question since I can't find it on google: Does anyone know what the
resistance of a coat hanger wire in a 5 gallon bucket of water is?

I'm working on testing these old hawkers in my driveway (EP26ah, sitting for
3 years or so, they were 5 years old before that, in other words probably
fine) and I have been working them in strings of 7.

Connections between batteries is 10g wire, I am using my large Sears charger
(up to 250a charge), and a coat hanger in water connected to jumper cables
for discharge.

The batteries will happily smoke the water, but my meter only shows 0 ohms
when I check at the jumper cables. I think it's pulling more than 100a since
the spark on disconnect is bigger than the spark on disconnect with the
charger, but it would be interesting to know how much.

The batteries will also happily peg the charger's meter to 250 using car
start mode on this charger (note, it's a big transformer charger, wheels and
all that, the biggest Sears one, not a little toy one) with a voltage of
12.5v @ "250a". Which I kind of doubt a bit since:

12v*250a=2,700 watts. Using my Watts Up meter I see it pulling 16a from
120v, so it's either over-unity or optimistic (maybe 100a)

However charging at 50a, the meter on the charger says about 50a, with a
voltage at battery of 13.0. The Watts up meter shows [email protected] 1080 watts.
Which would make the battery side 650 watts or an efficiency of about 60%.
Is that in line with a transformer based charger?

Thanks!
Chris

_______________________________________________
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