AGM Battery Charger Operation

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4Springs
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AGM Battery Charger Operation

Post by 4Springs »

I think that my battery charger is running the voltage a bit high on my battery pack.
I think I know what might be causing it.
I think I have figured out a way to fix it.
I may be wrong on any or all of the above three points, so I’d like to run it all past the knowledgeable folk here in the forum.

Ok, for the details:
I have a Chennic JCWP14408 battery charger for my 144V battery pack. Info here: Chennic
I have 12 x 12V AGM batteries (Century C12-140DA), and I am using the Zener diode battery balancing described here: Zener
I have just used significant current for the first time, so I am using the charger for the first time. I have a Watt meter on the 240VAC input to the charger, and a Volt meter on the battery pack. I’m seeing the following:

Scenario 1: A fully charged battery pack:
Turn charger on, power goes up to about 1.2kW, Voltage rapidly goes up to about 175VDC.After a few seconds, the battery charger shows its “full” light, and the power goes to almost nothing. Voltage steadily drops, and settles to about 150V.Scenario 2: A partially discharged battery pack:
Turn charger on, Voltage increases as expected up to approx 172VDC. Power drawn is about 1.4 kW. Charger shows a current graph initially at IIII (the maximum).Power drawn decreases as the voltage goes up. Current graph goes to III, II etc. Zener regulator light bulbs start to turn on, some glow brighter than others.Once the current graph is at I, the voltage is 184.5V. Regulator light bulbs are glowing brightly at this stage.Eventually the “full” light is lit on the charger, but the voltage stays at 184.5V. Power being drawn is about 600W. I have left it in this state for a while (50 mins) waiting for the charger to realise that it has finished, but it just continues. Regulator bulbs are glowing brightly, and zeners are warm to the touch.If I cycle the power to the charger at this stage, it goes through the steps described in scenario 1, and doesn’t try to charge any more.

So, is this voltage too high for my batteries? 184.5 / 12 = 15.4V per battery, / 6 = 2.6V per cell. 600W / 184.5V = 3A. From what I have read, this voltage for too long will result in gassing, not good for an AGM.

Reading the manual, I think that normal operation for this battery charger is to turn off once the battery is charged, perhaps at about 170-180V. It does this in the scenario 1, but not in scenario 2. It says that it has turned off, but the voltage and current tell a different story. I’m guessing that this may be because of my zener balancing. Perhaps the extra current drawn by the light globes is messing with the charger sensing?

My theory for a work-around is to put a light sensor (LDR I suppose) next to one of the regulator bulbs. When the globe has been glowing above a certain light level for a certain time (say 10 minutes), cut the power to the battery charger. Might be an idea to restore power after another 10 minutes, just in case something screwy is going on (like someone opens the battery box). Restoring power to the charger would be fine, based on the observations above.

Does this all sound reasonable, or am I barking up the wrong tree?
Last edited by 4Springs on Sun, 18 Mar 2012, 03:19, edited 1 time in total.
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coulomb
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AGM Battery Charger Operation

Post by coulomb »

4Springs wrote: I think that my battery charger is running the voltage a bit high on my battery pack.
I think I know what might be causing it.
So you think it was your zeners; that seems reasonable.
I have a Chennic JCWP14408 battery charger for my 144V battery pack. Info here: Chennic
My understanding is that Chennics are essentially re-branded Elcon/TCCharger. (Though I don't think that any Elcon/TCCharger have the current LEDs, IIII to I.)
Scenario 1: A fully charged battery pack:
Turn charger on, power goes up to about 1.2kW, Voltage rapidly goes up to about 175VDC.After a few seconds, the battery charger shows its “full” light, and the power goes to almost nothing. Voltage steadily drops, and settles to about 150V.
That seems fine, except I'd like to see it settle a little higher. But I think that means you're not quite at 100% SOC yet on all cells. From how the zeners come on at different times, it seems like the pack needs a lot more time to balance properly. That will likely come with more charge cycles.
Scenario 2: A partially discharged battery pack:
1. Turn charger on, Voltage increases as expected up to approx 172VDC. Power drawn is about 1.4 kW. Charger shows a current graph initially at IIII (the maximum).
2. Power drawn decreases as the voltage goes up. Current graph goes to III, II etc. Zener regulator light bulbs start to turn on, some glow brighter than others.
All you've said is good to this point, except:
3. Once the current graph is at I, the voltage is 184.5V.
I don't know all that much about SLA, but that's way past my comfort point. I'm confortable at 14.4 V per 6 cells, with the comfort decreasing about linearly to 14.7 V per 6 cells. 184.5 V is an average of 15.375 V per 6 cells. I don't believe that SLA should be anywhere near this voltage for more than a few minutes, and then only for an occasional equalisation charge, never for a regular charge. But I'd wait for others' opinions, who have actually used SLA in their EVs.
4. Eventually the “full” light is lit on the charger, but the voltage stays at 184.5V. Power being drawn is about 600W.
Well, drawing 600 W is hardly "turned off". Though 3.5 A (less 0.5 for the zeners) is pretty mild for what I'm guessing are nominal 140 Ah @ 1/20C cells.
Regulator bulbs are glowing brightly, and zeners are warm to the touch.]
Yes, they are only bypassing half an amp; that's 3.4 W for a 5 W zener. Do you have some really good heatsinking? If so around 2.75 A is going into the pack; actually if the efficiency is 85% at this current, it's more like 2.25 A, or C/50 for a 140 Ah pack.

I guess C/50 is pretty tame. So I agree with your theory; the zeners are affecting the way that the charger works. Going to such a high voltage, but at low current, may be normal for SLA charging.
Reading the manual, I think that normal operation for this battery charger is to turn off once the battery is charged, perhaps at about 170-180V. It does this in the scenario 1, but not in scenario 2. It says that it has turned off, but the voltage and current tell a different story. I’m guessing that this may be because of my zener balancing. Perhaps the extra current drawn by the light globes is messing with the charger sensing?
I'm thinking more like it's now in an area where the manufacturer hasn't done extensive testing, so it sounds more like a bug to me. Otherwise, why would it turn off in scenario 1?
My theory for a work-around is to put a light sensor (LDR I suppose) next to one of the regulator bulbs.
That could be made to work.

You might have another option. Elcons/TCChargers have a 7-pin round connector, which often comes with a short lead with perhaps 4 wires. Does yours have this? If so, you can possibly use this to cut back the current. I forget the details (Weber and I have the CAN version, where this doesn't apply), but you can set the voltage to between two levels and get from 0 to 100% of current (possibly limited if it things it should be limited, so you may only be able to cut back, not ramp up, the current). This might be tidier than cutting the mains input to the charger, and you might even get it into a "zone" like scenario 1 where the charger cuts off by itself.

But I don't see mention of this connector, and there are only two glands (presumably mains input and charger output) on the plan-view drawing. So maybe Chennics aren't so similar to Elcon/TCChargers after all.
Last edited by coulomb on Sun, 18 Mar 2012, 10:12, edited 1 time in total.
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AGM Battery Charger Operation

Post by 4Springs »

Thanks coulomb, it's good to see that I'm thinking along the right track.
Re the similarity between Elcon and Chennic chargers, I have a manual for an Elcon, although I haven't seen an actual charger. Although it is the same colour, and similarly put together, the shape is a bit different. Also, as you mentioned, the indicator lights are different. The Chennic certainly does not have the 7 pin connector you mention.

I have thought of one problem with my solution, in that it relys on the light globe working. If the globe blows, the charger goes back to its old tricks. A voltage sensing circuit would be more reliable, but I can't think of an easy way of making one.
Last edited by 4Springs on Sun, 18 Mar 2012, 11:54, edited 1 time in total.
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AGM Battery Charger Operation

Post by Johny »

I'd be concerned about anything over 14.4V per battery as well.
I think it would be worth going to the trouble to disconnect the zener balancing for your next "real" charge and see how it responds. The charger might be smart enough to be attempting an internal resistance measurement on the pack to determine its stage of life. The residual current that the zeners provide may well upset that.
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AGM Battery Charger Operation

Post by coulomb »

Johny wrote: I'd be concerned about anything over 14.4V per battery as well.
Though I found it interesting that Lee Hart (a well respected EVer, on the Zener page) says that Gels need the lowest charge voltage, then floodies, then AGMs the most voltage. He achieves the different voltages with different combinations of 6.2 and 6.8 V zeners in series.

How AGMs can deal with more voltage than floodies I don't know.
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AGM Battery Charger Operation

Post by Johny »

coulomb wrote:How AGMs can deal with more voltage than floodies I don't know.
Yes it needs a bit more research. My experience was way back with fork lift battery chargers so obviously flooded LAs.
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AGM Battery Charger Operation

Post by 4Springs »

Update time:
I decided that disconnecting the zener regulators was not worth it. My cost benefit analysis went something like this:
Cost: Disconnecting 12 terminals that are held together with loctite, cleaning the bolts up before re-assembling them again.
Benefit: It would be interesting to see what happens.

I built a circuit to turn off the battery charger when the light globes glow:

Image

The two LDRs are positioned next to two of the light globes on the zener regulators. So when they light up, the input of the first 555 timer (pin 2) goes high. This makes the output (pin 3) go low. R1 & C1 provide a delay, and then the input to the second 555 goes low. The output of the second 555 goes high immediately, and stays high for a few minutes, set by the variable resistor.
The output line goes to a normally closed relay in the 240VAC supply to the charger. So when the lights go bright for more than 50 seconds or so, the supply voltage to the charger is cut for 5 minutes or so. The relay then clicks off again, and connects the charger again.

It has worked quite well so far. I put in two LDRs as a bit of a backup. If one of the globes fails, then the other one may get bright enough to still set off the circuit. I will need to do a regular check that all globes are still working. This is easily done by cycling power when the pack is full - all globes glow for a few seconds while the charger is testing the pack.
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