More Charging Current for FLA Batteries?

[hotcoldsummer]

I noticed that my two 6v Duracell GC2 (Deka GC10) batteries run in series at 12v max out around 9 amps of current and average even lower when charging with my 55amp WFCO 8955 Power Center on shore power. Max current during bulk stage is stated at 30% of amp hours, so 64.5 amps if I'm understanding correctly. Wouldn't these batteries charge much faster with more current?

 

[sunshine_eggo]

Charging at > rated current does two things:

Charges a little faster
Notably shortens battery life.

The more likely issue is the issue in almost every RV... the shitty wiring between the converter and your battery. The converter "sees" 14.4V long before the battery actually gets there.

Next time it's charging, use a voltmeter and check the output of the WFCO at the unit and then check battery voltage at the battery terminals.

 

[hotcoldsummer]

Charging at > rated current does two things:

Charges a little faster
Notably shortens battery life.

The more likely issue is the issue in almost every RV... the shitty wiring between the converter and your battery. The converter "sees" 14.4V long before the battery actually gets there.

Next time it's charging, use a voltmeter and check the output of the WFCO at the unit and then check battery voltage at the battery terminals.

I understand the risk in pushing too many amps but 4-9amps out of 65 rated max is a big gap.

I'm confused as to how having line loss as a result of undersized wiring would cause undercharging. Wouldn't it cause overcharging as the converter would think the battery was slightly less charged than it actually was?

This wfco model seems to only go into bulk mode when the battery is really drained, like below 12v. Otherwise it outputs 13.7v to the battery, adding more current to compensate for any system load so the battery always shows 13.7v on charge.

I usually charge until its only drawing .5 amps, which is about what the system draws when nothing is switched on.

 

[Vigo]

If your wiring would cause a 1 volt drop @ 10amps, then the converter would see 14.4 while the battery was at 13.4. It would terminate charging early. Voltage drop scales with current so in any case, the voltage reading while ~0amps are flowing should be basically accurate.

As far as what charge current you're actually going to get, it's going to come down to basic ohm's law stuff. Your charge source is probably usually only able to raise voltage by tenths of a volt to perhaps 2v max above battery voltage, so you don't have a lot of 'pressure differential' in the circuit to start with. Then, that low voltage differential divided by the resistance of the circuit (which includes all the conductors and the batteries themselves) would basically determine what flow rate you get.

So really, assuming your charge settings are correct the main thing it would come down to is the conductors between charger and battery. I guarantee if you had an 'unlimited current charge source' at ~14.70v and hooked it directly to your two 6v batteries in series (acting as one unusually large 12v battery) you would get 10s of amps, possibly closer to 100a, but definitely not no single-digit BS number like 9. So it's very very likely to be your conductors/connections are just adding too much resistance to the circuit to flow a large current number with the small available voltage differential.

What is the circuit physically like? How many feet of wire between charger and batteries, what is the wire gauge, is it chassis grounded or have dedicated negative wire, etc. Pictures might help fill in context. If you are wanting to flow anything like 65amps over any kind of distance you are talking 4ga wire, maybe bigger if its a long wire run. That's similar size to the wire that goes from the battery to the starter under the hood of a car, so unless you already have some pretty big wire in there, that's going to be your limiting factor.

 

[yodamota]

you will only see max amps at bulk charging.... during absorption it will be less. are your batteries being run down?

 

[sunshine_eggo]

I understand the risk in pushing too many amps but 4-9amps out of 65 rated max is a big gap.

I'm confused as to how having line loss as a result of undersized wiring would cause undercharging. Wouldn't it cause overcharging as the converter would think the battery was slightly less charged than it actually was?

@Vigo explained it well.

There is a voltage drop from charger to battery. The charger will "see" 14.4V while the battery is at lower voltage and will likely terminate charge before the battery is ever anywhere near 14.4V.

This wfco model seems to only go into bulk mode when the battery is really drained, like below 12v. Otherwise it outputs 13.7v to the battery, adding more current to compensate for any system load so the battery always shows 13.7v on charge.

Not uncommon behavior. Often a full power cycle on the converter is necessary to trigger bulk. At 13.6-13.7V, it may take 24+ hours to fully charge the battery.

Double check that all your connections are properly torqued and secure to minimize voltage drop. Consider power cycling the converter to "boost" charge via unplugging or pulling the fuse/flipping the breaker for that circuit.

This is a pervasive issue with RV converters.

 

[hotcoldsummer]

Thanks for clarifying. This is a small teardrop camper and the run between the batteries and controller is about 6-8', all 8 awg wire. I calculated that 8awg at 8' should carry up to 30amps before other resistance so assumed that would be sufficient to get well beyond 4-9 amps. The batteries are in a sealed, vented battery box under a closet so there are a couple terminals in the circuit.

This is the wiring sequence:
Controller Pos>>>>>>Breaker>>>>>Battery Box Pos>>>>Battery Bank Pos
Controller Neg>>>>>>Smartshunt>>>>>Battery Box Neg>>>>>Battery Bank Neg

Since posting, I tested all six battery cells with a hydrometer and found the specific gravity to be about 1225 on all cells, so a little low. I'm wondering if there's been some sulfation. I've never equalized as a lot of people say there's no need with regular use. The only charger I have that will do it is my MPPT and I only have a 100w panel so assumed it might not get enough sun for long enough to complete the maintenance charge.

I just put a 4 amp load on the battery to test how long it takes to drain to around 50% to judge the battery health and then will test and compare the voltage at the controller and at the battery. I noticed a tiny bit of corrosion that I'll clean also but will wait until after I test.

 

[Vigo]

You're probably going to want to charge them more aggressively with a grid or generator powered charge source just so you can assess their health without so much waiting. If i had to guess i would say you are going to end up running more than one equalization cycle AFTER they are fully charged as verified by SG.

I highly recommend looking up the documentation online by Rolls and Trojan as even if the setpoints for voltage might differ slightly, there is a ton of information there to educate you about when and how to do equalization charging. It's possible you may not need to since your SGs are apparently all pretty similar, but if you find the batteries have weak capacity even after fully charged (as verified by SG), then you would either attempt to improve it through EQ cycles or just live with it until you buy new batteries.

 

[hotcoldsummer]

You're probably going to want to charge them more aggressively with a grid or generator powered charge source just so you can assess their health without so much waiting. If i had to guess i would say you are going to end up running more than one equalization cycle AFTER they are fully charged as verified by SG.

I highly recommend looking up the documentation online by Rolls and Trojan as even if the setpoints for voltage might differ slightly, there is a ton of information there to educate you about when and how to do equalization charging. It's possible you may not need to since your SGs are apparently all pretty similar, but if you find the batteries have weak capacity even after fully charged (as verified by SG), then you would either attempt to improve it through EQ cycles or just live with it until you buy new batteries.

I've read a bit of Rolls info on equalizing and seems the obvious reason to equalize is when SG varies between cells, which mine do not, though probably worth trying. I bought these batteries from Sam's club so hoping I might be able to have them replaced. Whenever I eventually have to buy new, I'm definitely going Battleborn lithium--so much less to think about.

 

[HarryN]

There definitely is some de- bottle necking that can be done to improve performance if that is what you are after.

There is nothing wrong with using 6 volt flooded batteries to make 12 volt packs but there isn't any advantage either other than it used to be a way to reduce the weight that was lifted. Now there are GC2s in 12 volts if you like that size.

A battery pack that size can easily handle an 800 - 1000 watt solar array if you have a place to put it - either on the trailer or some panels that you deploy where you get to where you are going. 100 watts is really just a trickle charger vs really powering anything. 400 watts is really the minimum size for solar to be interesting for camping IMHO.

A fuse block could be used to distribute power to each of your 4 battery "banks" with a 10, 8 or maybe even 6 awg wire (I need to check) using something like this.

ST Blade Fuse Block - 12 Circuits with Negative Bus and Cover - Blue Sea Systems

Compact ATO® / ATC® fuse block consolidates branch circuits and eliminates the tangle of in-line fuses for electronics and other appliances.

www.bluesea.com

The batteries could be upgraded to AGMs which have higher charge / discharge rates in many cases.

The charge rate from being plugged in is somewhat limited by how much power is available from the outlet and at 55 amps that is close to what many outlets can handle on a continuous basis.

Edit - just saw that you are looking at the BBs- good choice. They make a GC2 in 12 volts IIRC and it might be that their other sizes might fit in your setup.

 

[hotcoldsummer]

There definitely is some de- bottle necking that can be done to improve performance if that is what you are after.

There is nothing wrong with using 6 volt flooded batteries to make 12 volt packs but there isn't any advantage either other than it used to be a way to reduce the weight that was lifted. Now there are GC2s in 12 volts if you like that size.

A battery pack that size can easily handle an 800 - 1000 watt solar array if you have a place to put it - either on the trailer or some panels that you deploy where you get to where you are going. 100 watts is really just a trickle charger vs really powering anything. 400 watts is really the minimum size for solar to be interesting for camping IMHO.

A fuse block could be used to distribute power to each of your 4 battery "banks" with a 10, 8 or maybe even 6 awg wire (I need to check) using something like this.

ST Blade Fuse Block - 12 Circuits with Negative Bus and Cover - Blue Sea Systems

Compact ATO® / ATC® fuse block consolidates branch circuits and eliminates the tangle of in-line fuses for electronics and other appliances.

www.bluesea.com

The batteries could be upgraded to AGMs which have higher charge / discharge rates in many cases.

The charge rate from being plugged in is somewhat limited by how much power is available from the outlet and at 55 amps that is close to what many outlets can handle on a continuous basis.

Edit - just saw that you are looking at the BBs- good choice. They make a GC2 in 12 volts IIRC and it might be that their other sizes might fit in your setup.

Yeah, I opted for this setup because the price was really good for 215 amp hours and I thought the thicker plates might help them to last longer, though maybe that wasn’t the case.

I really don’t need a lot of power. I’m only running a Dometic CFX 55IM cooler around the clock. Beyond that, it’s just lights, water pump, etc. Even with the batteries in their current stage, I can go over 3 days with moderate Solar running the cooler before I start to get compressor fail errors.

 

[sunshine_eggo]

I've read a bit of Rolls info on equalizing and seems the obvious reason to equalize is when SG varies between cells, which mine do not, though probably worth trying. I bought these batteries from Sam's club so hoping I might be able to have them replaced. Whenever I eventually have to buy new, I'm definitely going Battleborn lithium--so much less to think about.

1.225 consistent may only indicate a reduced state of charge. If you're not getting to 14.4-14.8V at 0.02C current, you're not fully charged.

There is also a minimum SG. Rolls is below about 1.265 OR .03 variation.

Very important that you fully charge the batteries before attempting equalization. Premature equalization will damage the batteries. If starting from a full charging, ~7A from a 100W system might get you there.

3% is not desirable. Too much. You're building in a 0.4V drop at 14.4V.

What happens when you power cycle the converter? Have you measured voltage at the converter output and at the battery terminals per post #2?

Those posts also look quite corroded.

 

[hotcoldsummer]

1.225 consistent may only indicate a reduced state of charge. If you're not getting to 14.4-14.8V at 0.02C current, you're not fully charged.

There is also a minimum SG. Rolls is below about 1.265 OR .03 variation.

Very important that you fully charge the batteries before attempting equalization. Premature equalization will damage the batteries. If starting from a full charging, ~7A from a 100W system might get you there.

3% is not desirable. Too much. You're building in a 0.4V drop at 14.4V.

What happens when you power cycle the converter? Have you measured voltage at the converter output and at the battery terminals per post #2?

Those posts also look quite corroded.

I just cycled and tested the voltages:

13.7v at the converter
12.65v at the battery box terminals
13.35v on the battery posts.

I guess I need to clean the terminals and recharge. My converter states it will bulk charge at 14.4v but I've never seen it go beyond 13.7 but I guess this snippet from the manual explains it?


My MPPT bulk charges around the same but will rise over 14v if it hits absorption. Do I need to go buy a new charger?

 

[sunshine_eggo]

I just cycled and tested the voltages:

13.7v at the converter
12.65v at the battery box terminals
13.35v on the battery posts.

I guess I need to clean the terminals and recharge. My converter states it will bulk charge at 14.4v but I've never seen it go beyond 13.7 unless the battery is really drained. My MPPT bulk charges around the same but will rise over 14v if it hits absorption. Do I need to go buy a new charger?

I hope that's a typo... 12.65V at the battery box terminals? 13.65V?

Are your box terminals custom, or are they a product intended for that purpose? Do they rely on the threads to conduct current?

Assuming 12.65 is a typo, and you meant 13.65, an additional 0.3V drop between the top of the box and the batteries screams there's a problem.

Worth checking all connections for torque, pinched shrink, loose crimps, etc.

 

[hotcoldsummer]

I hope that's a typo... 12.65V at the battery box terminals? 13.65V?

Are your box terminals custom, or are they a product intended for that purpose? Do they rely on the threads to conduct current?

Assuming 12.65 is a typo, and you meant 13.65, an additional 0.3V drop between the top of the box and the batteries screams there's a problem.

Worth checking all connections for torque, pinched shrink, loose crimps, etc.

Sorry, typo.

13.7v at the converter
13.65v at the battery box terminals
13.35v on the battery posts.

They're battery box studs meant for this purpose--a brass post with top and bottom and a nut on each side to secure a ring terminal. The voltage is 13.65v on the ring terminal that connects to the battery also so the loss seems to be because of corrosion.

Once I fix the problem, is 13.7v enough to get these batteries fully charged? This is what my converter's manual says about bulk mode. Thanks!

 

[sunshine_eggo]

Sorry, typo.

13.7v at the converter
13.65v at the battery box terminals
13.35v on the battery posts.

They're battery box studs meant for this purpose--a brass post with top and bottom and a nut on each side to secure a ring terminal. The voltage is 13.65v on the ring terminal that connects to the battery also so the loss seems to be because of corrosion.

Once I fix the problem, is 13.7v enough to get these batteries fully charged? This is what my converter's manual says about bulk mode. Thanks!
View attachment 167126

With 0.35V drop at presumably low amps, this is quite excessive. The converter may refuse to go into bulk mode.

Resolve your voltage drop issue and then evaluate the converter.

 

[sunshine_eggo]

Stranded wire secured to that type of bus bar is a recipe for bad connections. You can see the frayed wires. Wires affixed in this type of bus bar should be tipped with a ferrule before installing.

 

[hotcoldsummer]

With 0.35V drop at presumably low amps, this is quite excessive. The converter may refuse to go into bulk mode.

Resolve your voltage drop issue and then evaluate the converter.

Thanks for the suggestions!

I will start by cleaning the terminals since that's where to majority of the voltage drop seems to be happening but adding ferrules is a good idea. That part was wired that way when I got the camper.

I just found this thread discussing the problem of the WFCO not bulk charging when you have a need to charge more quickly. It seems a lot of folks are using separate chargers in lieu of the WFCO, or swapping out the converter with a better one.

 

[sunshine_eggo]

It seems to need a dip to a lower voltage before it will bulk. If you can load the battery to the point that it pull the voltage down to something below 12.5V, it might trigger a rebulk once you engage the charger. A bit of a nuisance, but for campground queens that stay plugged into shore power a lot, it's probably the better option.

 

[hotcoldsummer]

It seems to need a dip to a lower voltage before it will bulk. If you can load the battery to the point that it pull the voltage down to something below 12.5V, it might trigger a rebulk once you engage the charger. A bit of a nuisance, but for campground queens that stay plugged into shore power a lot, it's probably the better option.

Yeah, or just hook them up to an automotive charger or use Solar to top them off over a couple days.

Reading that thread on these WFCO’s linked above, it seems they are more suited to basic 70amp hour lead acid batteries. I might eventually buy a 30amp Victron IP22 charger that I can use to charge and maintain with the battery disconnect switched off from the system. Plus, I’ll be set up for when I eventually make the jump to lithium.

I also consulted my wiring schematic and realized the trailer chassis is used between the battery and converter to ground the system so there’s a lot of opportunities for resistance. Luckily, it’s just lights, small electronics and water pump on the WFCO so nothing pulling significant amps.