agm battery charge issue

time2roll wrote:

LittleBill wrote:
my issue and my confusion, again is around 13.6v at the battery. PD is doing 14.4, but the amperage is going down around 20amps and still tapering, PD should be cranking the amperage up to get to 14, but its not doing it.

The PD only holds voltage. The battery pulls amps. Once the PD is hitting 14.4 it is done increasing and the amps taper. The PD has no idea what is at the other end of the wire. Only way to push more amps is to increase the supply voltage but the supply is topped out at 14.4 volts. PD can only hold the voltage and wait for the battery to catch up.

For fast charging the circuit voltage drop should be 200 mV or less at full current.

so my voltage drop only becomes a problem at 80% charge and not 20% charge?

my voltage drop is increased at the lower charge, why is it not affected there then?

the voltage drop is a sliding scale, shouldn't it be moving uniformly?

It is a mystery why it sat at 13.6 for an hour unless the CW got hit twice unaware

LittleBill wrote:
so my voltage drop only becomes a problem at 80% charge and not 20% charge? Yes at lower state of charge and even lower battery voltage the PD is not able to hold the voltage at 14.4 so the max amps flow.

my voltage drop is increased at the lower charge, why is it not affected there then? The voltage drop is fine until the PD hits the 14.4 limit and the amps start to taper.

the voltage drop is a sliding scale, shouldn't it be moving uniformly? As long as the PD is held lower than 14.4 volts the amps are at a fixed 45 maximum so everything is linear until the PD hits the 14.4 limit.

By reducing the voltage drop the PD will continue at maximum amps for a longer period into the charge cycle.

How large is the wire? How long is the wire?

20' charging loop of #6 wire will give .71 voltage drop. Plus a few connections and the circuit is at .8 volt drop. This is common for many RVs and makes fast charging a battery difficult.

well, ty. That took a little bit to wrap my head around. i guess remote voltage leads should be a thing so the pd can crank the voltage to get there.

at the end of the day its good enough for me, and probably will be irrelevant in a year when i prolly go LIFE

My opinion and experience--yours may vary:
From the discussion it does sound like there is possible voltage drop between the converter and the battery. As mentioned, don't forget the negative connection. My last 2 trailers used the frame for the return negative path (which also "grounds" the frame) with a whole bunch of negative wires lugged under two, too small, self-taping screw on the frame. Quite a bit of potential voltage drop as those connections would age. I added a solid negative wire in both cases.

However: why all the concern about getting to 14.4 on AGMs? While that will finish the charge faster, my Trojan T-105 AGM batteries spec a 2 hour limit at that voltage to avoid gassing. In addition, PD is real proud of their periodic 14.4 to prevent stratifying the electrolyte. But AGMs don't stratify so the period voltage blast is not needed. The PD rep that I last spoke with indicated that their research has shown that 14.4 will not hurt, but also is not needed.

The Trojan T-105 AGMs like to float at 13.5 and will get to 100% charge in a few hours with my charger set at 13.5 continuous. I verify this with a battery monitor. The last static test that I ran came up with .1 voltage higher than Trojan's full charge spec voltage (battery disconnected from load or charger sitting over night for 18 hours.)

What is the distance between the charger and the batteries? What is the wire gauge?

guys the charger was doing something weird to me, this rig is new to me, and the battery monitor system I added is also new, so I had a bit more insight. wire was added. at the end of the day I agree its voltage drop, but expected it to be a issue on a gradual scale, not towards the top 80%. After looking at the wiring it could be improved, but I'm not in a big rush, and I may do a major rewiring.

Thanks for all the info.

Little Bill,

I have just re-read your entire post. Nothing you are seeing is actually a surprise.

It is possible that you have gotten your head around the effects of voltage drop in the conductors. If one is dealing with this with no background experience, such confusion is to be expected. I have installed full battery monitors (both Bogart and Victon) on more than a few owner's boats in the process of an electrical upgrade.

If one is not aware of what a Progressive Dynamics 92XX can do, it will not make sense some times. The good thing is that I have only once actually disagreed, but that didn't really matter in the final analysis.

Let the PD do what it wants and watch the little flashing light and start to understand what it is about.

Matt