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Open Roads Forum  >  Tech Issues

 > PowerMax PM3B100 Test UPDATE vs Vectors

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BFL13

Victoria, BC

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Posted: 03/24/12 10:53am Link  |  Print  |  Notify Moderator

Here is a good example of what Salvo was saying about too high of a charging rate spiking the battery voltage up front.

Note-I can't just show the graph in the link so ignore the rest of that thread for this purpose.

In this case the initial charging rate was 130amps on est 270ah, or 48%. The bulk stage had no constant amps but the rising battery voltage did keep the tapering shape bulging up. Once absorption started with voltage held constant, amps tapered in the usual sagging shape.

In the OP case this thread with the 103amps on 226ah it was 45%. An interesting thing is that initial battery voltage did not spike very much. That was on 6s while the example here was on three 27s, which may be the reason for different spiking. Don't know.

Another point to note, is the three-level uggly graph shows the Vector charger method of tapering when battery voltage reaches 14v, while other chargers wait till a higher Vabs and hold that while amps then taper. Vector does it differently by allowing Vabs to continue to rise to 14.6-14.8 by the end, while amps taper, so you get higher acceptance rates as SOC climbs so that makes the tapering sag less.

(I see above I got mixed up between 80 and 100, but the point is the same, that these high amps on only a pair of 6s is within their acceptance at the high voltages in play or there would be no constant amps at all. This last graph shows a real case of overcharging, but no harm came to the batteries because they simply would not accept the amps (tapering instead) and the Vector's program doesn't force things.)

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23955590.cfm


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Salvo

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Posted: 03/25/12 12:39pm Link  |  Print  |  Notify Moderator

Battery "spiking" is an indication of battery health. What you're seeing is the I*R drop within the battery. I is the charging current and R is the battery bank internal resistance. The greater the resistance or charging current, the greater the voltage jump.

When I look at my (as well as Fisherguy's) pair of GC's charging test data, we have a voltage jump of about 1V when going from 0 to 60A. Battery resistance of a pair of 6V's is:

R_battery = 1V / 60A = 16.7 m ohm (for 6V pair)

B13's 4 GC have a resistance of 1.1V / 100A = 11 m ohm (for 2 6V pairs)

The 11 m ohm for 4 batteries equates to 22 m ohm for a pair of 6V's. Fisherguy and I measure about 16.7 m ohm of a pair of 6Vs.

Now looking at the 3 parallel 12Vs (from other link), the resistance is 2V / 130A = 15.4 m ohm. Each of the three 12V batteries has 46 m ohm! This is extremely large. It's an indicator the batteries are toast.

Now the million dollar question is why are they toast? Sulfation and not charging to 100% is part of the reason. IMO, charging at extreme rates will erode positive electrode material resulting in increased resistance.

Sal

BFL13 wrote:

Here is a good example of what Salvo was saying about too high of a charging rate spiking the battery voltage up front.


In the OP case this thread with the 103amps on 226ah it was 45%. An interesting thing is that initial battery voltage did not spike very much. That was on 6s while the example here was on three 27s, which may be the reason for different spiking. Don't know.



BFL13

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Posted: 03/25/12 01:34pm Link  |  Print  |  Notify Moderator

It is hard to know how much of the R is battery and how much is the tangle of wiring.

It could be I had too much in the wiring in the past. This winter I did some improvements with Salvo's help fighting those rascally mOhms. I now have the converter charging via the inverter so they both use the same wires from inverter to battery and there are the usual complexities with series/parallel and lots of connections. No doubt it could still be better.

Can't spiking be related to the current too, where there is too much wrt the capacity? In that case battery health would not matter?

I don't have the battery resistance calculations anymore I got with the various batteries back then when Salvo showed us how to do that, but those three 27s in the above link from early 2010 were not toast (yet) Got two more summers out of them, working them hard. They were banked with a pair of new 6s last summer to make a bank of five.

However, after that I did toss out the two older 27s last Fall and got two more 6s and still have the one newer 27. I used the 27 last month camping as a fifth battery and it did fine. Not sure what to do with it since it is not dead, but I don't really need it. I take it along as a sort of spare not hooked up.

SG on that 27 (from 3/10) - in the range of 1.265-1.275. Last load test on it was about 100ah

* This post was edited 03/25/12 02:00pm by BFL13 *

BFL13

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Posted: 03/26/12 10:01am Link  |  Print  |  Notify Moderator

I am pretty sure that high current on a small battery would make it spike where it wouldn't on a big battery, which is what I thought we were seeing here.

Another recharge on those same three 27s near the same time as that one above using three 35 amp Vectors at 105amps instead of the 130 amps got about 30 minutes of constant 105 amps before tapering nicely, so that looked good on the graph (which I can't find right now)

--The method Salvo posted before on taking battery resistance was quite complex and I am unclear how the above single reading method compares for accuracy.

If I get a chance, I will attempt the two-values method on each pair of 6s and on the 27 (which was one of those three) and see what that says. ( if I don't make a hash of it)

* This post was edited 03/26/12 10:12am by BFL13 *

BFL13

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Posted: 03/26/12 06:35pm Link  |  Print  |  Notify Moderator

Ok as seen in the other thread, using the more accurate method (discharge part), I got resistance of 11 mOhm on the 27DC and the same 11 mOhm amount for each pair of 6s.

I don't know how that works out for putting pair of 6s in parallel or 12s in parallel etc. Salvo's figures above don't seem right but anyway that's what it came to.

Whatever is going on with all that, I am confident my various batteires are in good shape based on how they work and their SGs, so it is just a matter of getting the new charging arrangements under control.

Salvo

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Posted: 03/26/12 09:38am Link  |  Print  |  Notify Moderator

Your wring tangle is out of the equation. Measuring the jump in battery voltage when applying a specific current will give us battery resistance and no info about cable resistance.

I notice the batteries were discharged to 12.18V. I assumed they started at 12.0V. Battery voltage jumped to 14.0V when 130A was applied. Total battery bank resistance is:

R_bank = (14.0V - 12.18V) / 130A = 14 m ohm

Each of the 3 batteries in the parallel bank have an average resistance of:

R_battery = R_bank * 3 = 42 m ohm

You were hitting these batteries very hard though, 0.36 C. It could be that resistance increases with higher charge currents and the results Fisherguy and I get (at 0.25 C) are not directly comparable to your resistance.

Sal

BFL13 wrote:

It is hard to know how much of the R is battery and how much is the tangle of wiring.



BFL13

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Posted: 03/26/12 07:54pm Link  |  Print  |  Notify Moderator

The graph on page three of this old thread shows those three 27s a couple of months later (when it was much warmer out and battery capacity was closer to it s rating of 360)that year (2010) being charged at 130amps. The first 50-90 before progressive losses started happening on subsequent recharges had a nice run of constant amps.

I don't have the voltages, but you can get an idea from the fact the amps begin to taper at 13.9v battery voltage when using Vectors, so initial voltage would have been low to mid 13s and took half an hour to get to 13.9.

As sulfation set in for each cycle, of course resistance got more, so amps tapered sooner each time, meaning voltage rose faster each time, which is what Salvo is saying should happen

I don't have much of my old data left on all this- I thinned out my pile of notes recently. (So of course now I wish I hadn't)

http://www.rv.net/forum/index.cfm/fuseac........d/tid/24204584/srt/pa/pging/1/page/3.cfm

Salvo

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Posted: 03/26/12 07:30pm Link  |  Print  |  Notify Moderator

Your batteries may be in good shape now after tossing the bad 12V batteries. The bank you tested 2 years ago was suspect.

The discharge resistance will be less than the charge resistance you just verified.

Why not check charge resistance with a bank of 3 batteries. Charge with 130A and see how much the battery voltage increases within the first minute.

R_charge = V2 - V1 / 130A

V2 is voltage after 1 minute @ 130A.
V1 is voltage before charging begins (make sure surface charge is removed).

BFL13 wrote:


Whatever is going on with all that, I am confident my various batteires are in good shape based on how they work and their SGs, so it is just a matter of getting the new charging arrangements under control.


mena661

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Posted: 03/28/12 12:45pm Link  |  Print  |  Notify Moderator

How the hell could I have missed this!!


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mena661

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Posted: 03/28/12 06:57pm Link  |  Print  |  Notify Moderator

Was getting it to boost at 50% repeatable? Or did you find you had to draw them down a little more to get boost?

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