Charge Current Questioin

OP: The WFCO 8955 is a 3 stage, 55 amp converter, and should send 55 amps even through the 6 gage wire. I would expect to see 14.4 volts for at least 1 hour, then drop to 13.6 for quite a while, then 13.2/13.3 volts. Watch your converter closely, as it may be dying. They start acting weird before they die completely. Our MH came with a 40 amp that died, and replaced with a 75 amp, which has just died, and replaced with a Power Max RV Converter Battery Charger PM3-55 AMP. The 75 amp lasted longer the than 40 amp, but used 1,300 watts of AC power. When we boondock, we use a 2,000 watt inverter generator, which is only rated at 1,600 watts continuous load. It did not leave enough head room on the generator to operate other items in the MH.

Here a response from Trojan regarding charging current, 10-20% C20

'Below is Trojan Battery's response:
There is really no limit to how high the initial charge current can be. We recommend that range of charge currents because charge systems are usually power limited and so we have to give customers a range. There are two things that you have to watch for when using high currents to charge batteries. The first one is that the current must be lowered before the batteries reach a voltage of 2.35 volts-per-cell. The second one is that the battery does not exceed 114°F. The only real advantage of having high charge currents is shorter charge times, but the implementation costs are usually too high.'

Another thing to keep in mind that there can also be a maximum recommended current for particular type of battery, say 0.3 of the battery capacity. Check the battery manual.

mbopp wrote:
13.6 volts - Is that what you measured on the battery when you took the current readings? Where did you measure the voltage - on the battery, or at the converter?
I'd have expected the WFCO to start at 14.4 volts in "bulk" mode.

,He has a WFCO,he will never see 14.4.
in 6 years never saw 14.4,but was a good charger at 13.6 at charger and 13.35 at batts

One thing to remember when checking amps with a meter. The number of amps read at any single time is a "rate" (like mph in a car). In order to have 29 amps added to the battery, that rate would have to read the same at the end of one hour.

In your case (29 amps near start/ 22 amps @ 1/2 hour), calculation: 29 + 22 / 2 = 25.5 amps x 0.5 (since only checked for 1/2 hour)= 12.75 amps was all that was added to your battery in that amount of time.

Since a battery is not 100% efficient in accepting charge you would have needed at least 2 hours of generator time to reach anywhere near 90%soc. The single battery will resist charging as it continues and the drop in charging rate while be somewhat linear. You would be lucky to get another 10 amps added by the end of the second 1/2 hour, for a total of 22.5 amps.

OH, proper max charge for a Group 24 is around 30 amps (Wet or Maintenance Free) LIfeline AGM it's a bit more (Quite a bit more) but that only applies that that specific brand. Gel (If you found one) is less, like 20 15-20 max.

I agree with "smkettner". Per your last reply using a single G24 battery and 6-gauge cable you got about as good as could be expected.

Your current setup is overkill for a single battery. Adding a second battery will make better use of a 55 amp 3-stage charger and give you more capacity before reaching 50%soc. The cable should be 3AWG or better depending on distance between charger and battery-bank.

A single AGM battery will also accept higher amps than a conventional acid/lead battery.

8955 has 55 amps available in all modes.
In your case of a small G24, the battery decides how much power it will accept.

Appreciate everybody's posts. I had plans to dry camp for few weeks, but I had an opportunity to get a full-hookup so I did.

Anyhow, I didn't watch things as close as I should have the first and only night I dry camped and woke up in the morning with my battery discharged to 11.9 volts. Cranked up my generator, turned off everything (12 vdc & 120 volt), turned on the converter and started to charge the battery. Within a minute or two of starting the charge I read 13.07 volts and 29 amps (clamp-on meter) at the battery terminals. Current dropped to 22 amps (voltage increased to 13.25 volts) about 30 minutes later. BTW, there's about an 8-9 foot cable (6 gauge) that runs from the converter to the battery (single 24 series battery).

I confused why I'm reading 22-29 amps (during the first 30 min.) on the battery terminals when the WFCO 8955 is supposedly in the 13.6 volt absorption mode. Isn't the charge current for the 13.6 absorption mode much lower, like 10-15 amps?

Thanks!

otrfun wrote:
With no load on the battery, converter on (WFCO 8955), and battery discharged to 11.9 volts (I know, not recommended), I read 29 amps of current on the negative battery lead (hard to access the positive terminal). This dropped to 22 amps about 30 minutes later.

1. Can I assume this is charge current?

2. Typically what is the maximum charge current when charging at 13.6 volts?

Thanks!

Yes it is charging current.

When charging started at 11.9 volts (read across the battery-terminals), your converter/charger would have started outputting 55 amps @ about 14.2 volts at the charger's terminals, after assessing the battery charge state.

The voltage reading at the battery-terminals would slowly increase from the 11.9 volt reading to 14.2 volts over around 15 minutes or more of charging time. The batteries are readily accepting the charge at that point so the voltage needed to force the charge is not yet read across the battery terminals.

I would add that it looks like you do not have the necessary gauge cables to see 55 amps current, at this stage, reaching the batteries.
I would be seeing 45 amps from my WFCO 8945 converter/charger.

Most 3-stage chargers would output 15 amps when in "absorption" mode (around 13.6 volts). The current (amp) reading will lower in either mode as the batteries start to resist charging as they near current capacity.