Charging/ Battery Charger?

[Murph60]

Hi All,

I have 2 100 AH AGM, group 27, batteries connected in parallel, but when I bought my 7 stage charger I was only considering the AH for a single battery, instead of the combined AHs for charging both batteries at the same time.

Fast forward and yesterday hooked up the charger, neg on one batt and pos on the other batt, to charge at the same time. It took ALOT of time for the charger to get past Bulk to Absorption. I connected it at 11 AM and was still only at Bulk when I went to bed last night, This morning it was at Absorption. I found that the charger was only good to 120 AH and has a 5 Amp output. When I bought the charger I was thinking charging one at a time.

So I decided to only charge one at a time. Disconnected the charger, hook up to only one battery. It only took a few minutes to go from Bulk to Absorption, which I kind of expected. That is where it is now on just one battery.

I hope I did not do any damage to the batteries when I unhooked the charger when I went to charge only one battery. Thoughts on this? Please tell me I am ok. LOL

Is there a recommendation on a multi phase charger for charging 2 100 AH AGM batteries in parellel?

Thanks all. Any input is appreciated.

[TitanMike]

When suzing a Converter/Charger its recommended it be up to 25% of the total battery bank size. A 200 ah battery bank (lead acid) should have a 50 amp Converter/Charger minimum.

If just a charger 50 amp is adequate for above as lead acid batteries only accept a max charge rate of .2 C to .3 C due to their internal resistance. LiFePo4 batteries can typically accept .5 C.

If a Converter/Charger, it needs to be large enough for all the DC current requirements when on shore power. That said, anything above the 25% of battery bank size won't really make any difference in charge time.

Generally, plan on 10 hours for a complete charge from 50% discharge to complete all charge stages with properly sized charger. First phase will go quick with the rest taking much longer.


Just curious. What size and brand is your converter. Generally they will charge as fast and as well as separate chargers as long as the wuring is adequate. Adding heavier gauge wire is usually cheaper than separate chargers of the same size znd a lot less hassle.

[rsdata]

I hope I did not do any damage to the batteries when I unhooked the charger when I went to charge only one battery. Thoughts on this? Please tell me I am ok.

Assuming you dis-connected a cable from one of the batteries so they are no longer paralleled?

A 5 amp charger is going to take some time charging both batteries... and it can be done
BUT
charging one at a time is counter-productive since they will be paralleled when being used, therefore the lower battery will discharge the higher battery equalizing them both.

[JLeising]

Charging at low current will be slow, but won’t damage the batteries. If the charger “stays in bulk” longer than it is designed to, the charger may be damaged…
If I understand your post, you charged the batteries is parallel until in absorption mode, then disconnected the batteries from each other, and connected the charger to one of the batteries. The charger then switched from bulk to absorption quickly. As, from my understanding of your process, that battery had already been charged (in parallel with the other battery), it seems quite reasonable that it took minimal time in bulk mode.
Charging two in parallel should take ~twice as long to reach any charge point.
If your batteries are connected to your RV, and when you disconnected the parallel connection between them you isolated the battery you subsequently connected the charger to, it is possible that parasitic current used by the RV was diluting your charge current, and you eliminated the parasitic current from the separated battery - allowing 100% of the charge current to go to the battery. As an example, if your RV has 3 amps of parasitic draw, with the batteries in parallel and connected to the RV, your 5 amp charger would supply 3 amps to the RV parasites and only one charging amp to each battery. The separated single battery would get the full five amps from the charger.
Wouldn’t worry too much about charging the batteries separately. Just charge them both fully before connecting them back together to avoid a large current surge through the parallel cables when you reconnect them.

[Murph60]

So if charging seperatly i should remove the parellel cables between the two?

[rsdata]

So if charging seperatly i should remove the parellel cables between the two?

I don't believe you gain anything charging separately...

If you are using an additional charger above and beyond the CONVERTER in the RV that gets power from the pedestal and charges the batteries...

THEN I WOULD disconnect the battery lead that feeds the trailer when charging the two batteries together... you want them to work together therefore you need to charge them together.

[Murph60]

Makes sense. Rookie mistake. I have now disconnected the parellel cables to charge a single battery at a time

[Murph60]

Originally Posted by rsdata

I don't believe you gain anything charging separately...



If you are using an additional charger above and beyond the CONVERTER in the RV that gets power from the pedestal and charges the batteries...



THEN I WOULD disconnect the battery lead that feeds the trailer when charging the two batteries together... you want them to work together therefore you need to charge them together.

Understood and will get the appropriate charger soon as i would rather charge both at same time.

Anyone have a recommendation on a charger for this set up?......2 x 100 Amp hour AGM batts

[rsdata]

Makes sense. Rookie mistake. I have now disconnected the parellel cables to charge a single battery at a time

I must NOT have been clear in post #6

You gain NOTHING charging each battery separately when you have them act in parallel when in use...

Keep them equal keep them in parallel when in use and in charging.

DISCONNECT the one + cable from the main trailer ONLY if using a separate charger as you indicated that you did in the original post. I am NOT talking about the CONVERTER which charges your batteries from the power pedestal.

[Murph60]

Originally Posted by rsdata

I must NOT have been clear in post #6

You gain NOTHING charging each battery separately when you have them act in parallel when in use...

Keep them equal keep them in parallel when in use and in charging.

DISCONNECT the one + cable from the main trailer ONLY if using a separate charger as you indicated that you did in the original post. I am NOT talking about the CONVERTER which charges your batteries from the power pedestal.

You were very clear, and i agree, but does no good if i dont hsve the correct charger for charging both in parellel.

[pgandw]

Originally Posted by Murph60

You were very clear, and i agree, but does no good if i dont hsve the correct charger for charging both in parellel.

What is wrong with the converter in your camper? Your A-frame came standard with a WFCO 35 amp converter. If you replaced the converter, what did you replace it with?

Having a larger capacity converter/charger speed up ONLY the bulk mode charging of a large battery bank. When the converter switches to absorption mode, you are only charging at about 5-10 amps per battery (amps decrease as battery becomes fully charged). Trickle mode charging is even less. So unless you new converter is rated at less than 20 amps, your batteries will not charge significantly faster even if you had a 50 amp converter/charger. The only impact of a "too small" converter is on the bulk charging, where it might take bulk mode 4 hours instead of 3. The other modes will take about the same time - 4-5 hrs regardless of converter size.

On my A-frame, I replaced the WFCO converter with a Progressive Dynamics 35A converter. I have 2 GC-2 batteries rated at 210AH, so the converter is slightly under-size for maximum charging speed. But since I'm not using a generator, but recharging from shore power, saving an extra 30 minutes (at most) is meaningless.

Fred W
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[NJKris]

I bought a 25 amp CTEK smart charger before I got the RV, to charge my golf cart batteries on the soon to be delivered RV. It was quite expensive. I didn't realize at time that my converter in the RV was capable of 35 amp charging. I've been using the charger for other vehicles, but it was kind of a waste spending hundreds on a charger when my RV converter can charge faster!

[Murph60]

OK so I am confused and appreciate all the help. By using the TT converter are you saying that would be your charging device and no need for a separate charger? I don't yet have an adaptor to plug into the house and I don't have any 30 amp circuits and would probably trip a breaker. Correct?

Sorry, I thought it would be best to use a separate multi-phase charger. Does the TT "converter" provide the bulk, absorption, and float phases that a separate charger would provide?

Could I get the same results but running my 4000 watt generator to charge the TT batteries?

Sorry for the newbie questions, but electrical is not my forte, but getting up to speed.

Again many thanks

[rsdata]

OK so I am confused and appreciate all the help. By using the TT converter are you saying that would be your charging device and no need for a separate charger?
CORRECT

I don't yet have an adaptor to plug into the house and I don't have any 30 amp circuits and would probably trip a breaker. Correct?
NOT CORRECT... UNLESS YOU RUN AN AC UNIT IN THE CAMPER YOU WILL PROBABLY NOT TRIP A BREAKER

Sorry, I thought it would be best to use a separate multi-phase charger. Does the TT "converter" provide the bulk, absorption, and float phases that a separate charger would provide?
LOOK UP THE MODEL NUMBER OF YOUR PARTICULAR CONVERTER UNIT... ALL HAVE SOME CIRCUITRY TO PROVIDE THOSE CHARGING PHASES, SOME BETTER THAN OTHERS, SO
NOT INCORRECT, BUT SEPERATE CHARGER NOT NECESSARY... IF BOTH HOOKED UP THEY WILL CONFUSE EACH OTHER AND NEITHER WILL FULLY CHARGE THE BATTERY(S)


Could I get the same results but running my 4000 watt generator to charge the TT batteries?
AT THE PRICE OF FUEL THESE DAYS?

Buy yourself this adapter and plug into household current 24/7 to keep batteries charged.

[pgandw]

Yes, your stock WFCO 8735P converter in your A-frame - if working correctly - is better than most stand-alone battery chargers (some high end multi-stage models might be a little better).

Unfortunately the two WFCO 8735P converters in my A-frames did not meet their own factory specs - they just sat at 13.7V, no matter what. In both my A-frames, I replaced the WFCO with a Progressive Dynamics 4135 "drop-in" replacement (about $150 IIRC), which works correctly in all 4 modes.

It took checking my DC voltage every day to determine the WFCO never went into the bulk or trickle charge modes. In both A-frames, I ended up installing a small digital voltmeter ($7 on Amazon) just above the fire extinguisher by the door to monitor the converter when plugged in, and approximate battery state of charge (SOC) when dry camping. I put a switch on the voltmeter because the digits were too bright at night to leave on.

The WFCO 8735 3 charging states:

- bulk. 14.1 - 14.4v, converter cooling fan will be on. Generally doesn't last more than 3 hours, usually considerably less (like 20 minutes). This mode won't be used at all unless battery is down around 50% or less SOC. And many WFCO converters will not work at all if battery gets below 11v.

- absorption (WFCO call this "normal mode" in some of their literature). 13.7 - 13.8v, fan usually does not run. WFCO switches to normal mode quite early, increasing time for total charge.

- trickle mode. 13.1-13.2v, fan does not run. WFCO says after 44 hours stable in normal mode, will switch to trickle mode. My WFCO converters never switched to trickle mode, causing over-charging and excessive water use in batteries.

Use an adapter to plug your 30 amp cable into a house 15 or 20 amp circuit. A 35 amp converter will use less than 500 watts in worst case, usually less than 100 watts. My A-frame Cool Cat air conditioner runs just fine on a 15 amp circuit in the garage, along with the converter, and the fridge running on AC (160 watts). I don't use the microwave in the garage - the Cool Cat and microwave together would probably trip the house circuit breaker.

hope this helps
Fred W
now 2019 Flagstaff T21TBHW A-frame
prev 2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states on weekend at a time

[tomkatb]

A “converter is really a fancy multi stage computer controlled battery charger!

Mine charges the battery at 60 amps. Cost over $200.

If I plug virtually any generator into the shore power it charges the batteries at 60 amps dc. That is 6-7 amps ac to the generator. Thus recharges a battery bank fairly quickly.

My Honda 2200 generator has a battery recharge connection. However it is about 8 amps dc as I remember.

The best/fastest way to recharge is using the converter. Solar is great for topping off. Unfortunately on its best day a 100 watt solar panel nets only 25 or so amp hours per day. That is 50% of most converters performance for an hour.

There is really no reason to carry a separate battery charger in the rv.

[NJKris]

The old days, converters were not as good as a multi-stage smart charger. Now the converters pretty much work the same as a smart charger, with multi-stages.

[Murph60]

Originally Posted by rsdata

OK so I am confused and appreciate all the help. By using the TT converter are you saying that would be your charging device and no need for a separate charger?
CORRECT

I don't yet have an adaptor to plug into the house and I don't have any 30 amp circuits and would probably trip a breaker. Correct?
NOT CORRECT... UNLESS YOU RUN AN AC UNIT IN THE CAMPER YOU WILL PROBABLY NOT TRIP A BREAKER

Sorry, I thought it would be best to use a separate multi-phase charger. Does the TT "converter" provide the bulk, absorption, and float phases that a separate charger would provide?
LOOK UP THE MODEL NUMBER OF YOUR PARTICULAR CONVERTER UNIT... ALL HAVE SOME CIRCUITRY TO PROVIDE THOSE CHARGING PHASES, SOME BETTER THAN OTHERS, SO
NOT INCORRECT, BUT SEPERATE CHARGER NOT NECESSARY... IF BOTH HOOKED UP THEY WILL CONFUSE EACH OTHER AND NEITHER WILL FULLY CHARGE THE BATTERY(S)


Could I get the same results but running my 4000 watt generator to charge the TT batteries?
AT THE PRICE OF FUEL THESE DAYS?

Buy yourself this adapter and plug into household current 24/7 to keep batteries charged.

Thank you. Very much appreciated

[Murph60]

Thanks All. learning something new every day with my first rig.

[TitanMike]

Originally Posted by rsdata

NOT INCORRECT, BUT SEPERATE CHARGER NOT NECESSARY... IF BOTH HOOKED UP THEY WILL CONFUSE EACH OTHER AND NEITHER WILL FULLY CHARGE THE BATTERY(S)

This is purely an Internet Myth although a popular one.

When multiple charge sources are connected to a battery bank EACH will contribute a portion of the charge current. When the battery voltage rises to whatever level the charge source is programmed to switch to the next lowest charge rate (Bulk to Absorption, Absorption to Float) they will do so and if the other sources haven't reached the programmed voltage yet, they will continue to charge.

When the highest voltage for any of the charge sources is reached then the last one still charging will close down to Float voltage output.

The batteries will reach full charge and no single one of the multiple charge sources can change that.

This myth comes from a lack of understanding how charge current, Voltage, and Charger regulation algorithms work. It's kind of like filling a water pressure tank with three different hoses attached, each with their own regulator. The final tank pressure will be the same as the highest regulator setting. Until the lowest pressure has been reached ALL hoses will contribute what they can to the volume and in the end the tank (PRESSURE) will be "filled".

In closing, this is how charging from Converter/Chargers, Tow Vehicles/Coach Alternators, and Solar, can all occur at the same time without any one of those systems being "confused".