Charging Multiple Batteries with Smart Charger?

[South Coast Stu]

I've spent a couple of hours searching on here and haven't found an answer to my question so figured I could go ahead and post. This question must have come up before

Trailer is a 2003 Bigfoot 21RB with a Magnetek 6300A converter. I have a 12V group 27 RVDC (100 Amp-hours) battery mounted by the hitch. I have 4 12V group 24 RVDC (75 Ah each) batteries connected in parallel in the bed of the pick-up truck. I also have a Perko switch (1-All-2) mounted to the battery box so that I can select between the trailer battery, the truck batteries or both. I have dedicated wires (+/-) that run from the Perko switch to the truck ("umbilical cord") with a quick connect.

This set-up has been working well for many years and multiple long-range trips. I typically get about a 1.2 amp charge from the pick-up while driving. When parked I either plug into shore power or a Honda 2000i generator and use the on-board converter to charge the battery bank.

Recently I noticed the trailer battery was getting run down. When I checked the current going to the battery from the converter I got zero amps which explained why it was getting run down I did find some posts on repairing the Magnetek converters but it sounds like a nightmare.

Rather than spend time/$ on the Magnetek I'm researching upgrading to a smart charger to charge more efficiently. I'm looking at a Noco Genius G15000 https://www.walmart.com/ip/Noco-Geni...Start/46605769 . It's rated to charge up to 400 Ah batteries. I would mount it in the trailer and hard wire it into the trailers 120 VAC system, that way it would charge the batteries when I'm hooked up to shore power or running the generator.

My question (finally) is if the G15000 is hooked up to one of the batteries in the series (or maybe the Perko switch?) will it work as it is supposed to? I found this: https://no.co/support/series-and-parallel-charging on Noco's web-site and it's leading me to think that it will not. Do I need something like the G4 https://www.walmart.com/ip/NOCO-Geni...arger/46606184 that is designed to charge a bank of 4 batteries (I would get rid of one of mine)? The price is about the same, however I would need to run a set of wires to each battery separately. The G4 also doesn't appear to have the advanced functions.

Anyone out there have experience with using a G15000 (or similar model) to charge multiple batteries in parallel? Thanks!

PS: I'm not totally set on the Noco Genius, they just seem highly recommended and have some very good functions/modes. Any input is welcome.

[John in Santa Cruz]

12V batteries in parallel act like one bigger 12V battery. downside is, as batteries age, they weaken, and they don't do it evenly, and a weaker battery will drag the stronger battery(ies) down with them

anyways, you should be able to charge them as one big battery, same as you have all along.

For what its worth, an RV power converter is designed to act as a power supply for all the DC loads as well as a battery charger.

[Franswa]

I got your private message, here's my reply....


yes, I'm the guy that deleted the converter entirely when it failed (like yours apparently did). From the power center I kept the AC and DC panel (breakers and fuses)...and re-located it to a more convenient location.


I had an extra AC circuit/breaker, so I installed an outlet on that and the charger is plugged into it...so if I want to turn the charger off I trip that breaker. In normal use, the breaker just stays on, when I plug into shore power the charger starts up and does it's thing. Never mess with it, really.


The charger comes with a lot of user defined settings...there must be a small battery in there because it "remembers" what setting it was on last time....powering the unit back on, it always goes back to the setting it was on the last time it was used. So you pick the setting for your particular system once and you never have to touch/fiddle with it again.



Mine is the 7200...my thinking was that 7.2A was more than I would ever demand from my electrical system at any one time. (If you carry that many batteries and a generator you probably would use way more than me so the 1500 is probably a good choice) The owner's manual states that these chargers can be used as stand alone power sources. They are double insulated so there is no fan (fan noise can be real annoyance IME depending on where it's mounted)


My battery bank is two six volt batteries in series...My charger is mounted "semi-permanently" so I can take it out easily and use it elsewhere if the need ever came up.


I'm happy with the charger. I have not experienced any negatives of living without a converter....so if I were you, I would calculate what your max power use would/could be ....if it's not above 15A (your NOCO) I would think that your experience would be the same as mine (if you decide to go without converter).



Good Luck, F

[Franswa]

Originally Posted by John in Santa Cruz

For what its worth, an RV power converter is designed to act as a power supply for all the DC loads as well as a battery charger.

I'm not sure if this applies to ALL systems...but in my old power center....there were three circuits powered by the battery/ies at all times even when the converter was on. From what I've read, it's because converters can induce "hum" to sensitive appliances like radios and TVs....so they provided three circuits for such items. When the converter was on, it did NOT power those circuits. (as far as I could figure out)

[South Coast Stu]

Thanks for the come-backs To clarify, I'm not going to eliminate my converter, just not use it to charge the batteries. The converter is (currently) working fine for everything else (120 VAC and 12 VDC loads).

Will the weakest battery in the "chain" prevent the G1500 (or other smart charger) from fully analysing and charging the other batteries?

Franswa - I would think the G7200 would "sense" the 2 6V's in series as just one big 12V battery.

Thanks again.

[Franswa]

"Thanks for the come-backs To clarify, I'm not going to eliminate my converter, just not use it to charge the batteries. The converter is (currently) working fine for everything else (120 VAC and 12 VDC loads)."





I'm certainly not an electrical engineer....but that worries me: You're going to leave a converter that you think doesn't charge your batteries but powers everything else ok (????) and then add a charger to that mix ???? I really can't say if that is advisable or not. In my case things were simple to figure out...once the converter was gone all I had to do was figure out the relationship between the battery, charger and panel...that was pretty simple.



and BTW the converter has nothing to do with the operation of your 120 VAC...except it gets it's input power from the AC panel.

[Franswa]

your best bet would be to go to an RV dealer....the converters are so prone to failure in these power centers that a whole sub-industry was created and there are now drop-in replacements for the whole "bottom half" (converter/charger) of most power centers....you give them your make/model number they reference a particular unit that fits right in...only four wires to cut/change...with detailed instructions...



I looked into to that...it was dead simple to swap out, the charger was very good/smart it looked like....the only downside for me was the cost at around 300 bucks where I found it. (in the US and in US$ you're probably looking at half that price)... Plus I wanted to experiment a little with a "batteries only" option.

[John in Santa Cruz]

Originally Posted by South Coast Stu

Thanks for the come-backs To clarify, I'm not going to eliminate my converter, just not use it to charge the batteries. The converter is (currently) working fine for everything else (120 VAC and 12 VDC loads).

Will the weakest battery in the "chain" prevent the G1500 (or other smart charger) from fully analysing and charging the other batteries?

Franswa - I would think the G7200 would "sense" the 2 6V's in series as just one big 12V battery.

Thanks again.

if the converter is connected to the DC loads, and the battery is connected to the DC loads, then the converter is connected to the battery, and WILL charge it any time the converter output is at least 1V higher than the battery output

[redbarron55]

Currently I have a Scamp with one large deep cycle ~ 100 AH 12 volt battery with a PD4530(If I remember correctly) and a Evpower Tracer MPPT solar controller and 300 watts of solar panels.
The blue breaker in the PD4530 powers the built in charger and the solar is hooked directly to the battery all of the time. I can parallel the two to charge from AC.
The charger feeds the battery directly and the solar controller feeds up to 40 amps to the PD4530 DC buss so that it can track power usage from the battery.
I also have a quick connect to add a second twin battery that I use sometimes in my boat for a trolling motor giving 200 AH total for 100 AH usable power.
Add to this there is a switch and a second quick connect to hookup a ham radio for emergency response. This circuit is good for 30 amps to handle the transmitter current loads.
I plan to replace those batteries with two six volt golf cart batteries when they reach their end of life.
All of the above must be to put off having to say that parallel 12 volt batteries are not optimum as they will not take charge evenly depending on their internal resistance.
The lower impedance battery will take more of the current and the higher less.
This means that the weaker battery will get the lower charge rate. If they are connected and on a charger that is three or so stages they will get charges as the charger changes the float and bulk charge voltages and currents and occasionally goes higher to "Churn" and desulphate the batteries.
All of that said the voltage on the batteries will be the same, but the current to each will be different. You could easily have all of the current going to one battery and none to the other.
By the way the bad battery COULD take all of the charge if the lead sulfide that flakes off the battery plates and falls to the bottom of the cell shorts out one or more cells it will reduce the voltage by 2 volts per cell and lower the voltage of the battery and reduce the impedance as well and this would "suck" in all of the current and also tend to overheat and boil out the electrolyte.

[Wayne Collins]

Two or more batteries can be charged together as long as they are connected in parallel. Best if there is no load on them while charging.

A company called Sure-Power Industries makes a device that will charge two batteries alternately. so that each gets to a full charge.
This is especially important with a 24 volt system using two 12 volt batteries in series.

[Raspy]

Whenever you charge two batteries in parallel, it's best to connect the charger's pos lead to one battery and the neg lead to the other battery. This will charge them with the same amount of current and they will reach the same state of charge. If you connect both leads to one battery, the second battery will get less.

[Wayne Collins]

Originally Posted by Raspy

Whenever you charge two batteries in parallel, it's best to connect the charger's pos lead to one battery and the neg lead to the other battery. This will charge them with the same amount of current and they will reach the same state of charge. If you connect both leads to one battery, the second battery will get less.

Maybe not. only if you don't have good clean and tight clamps on the posts.

[Raspy]

Originally Posted by Wayne Collins

Maybe not. only if you don't have good clean and tight clamps on the posts.

There's more to it than that. And, of course, the connections need to be clean. This is not done to compensate for bad connections.

I've been able to measure the difference in battery voltage when the charger is connected to only one battery, in a parallel group, and it makes sense, since there are different paths to each battery unless the charger leads go to separate batteries. Now imagine if you had six batteries in parallel and you only hooked up to the end one. It becomes more obvious why this is a poor practice. The current path to each battery must have the same resistance for them to charge evenly.

This also holds for the loads applied to the batteries. The + to one battery and the - to the other battery, in a parallel group.

[Wayne Collins]

You are assuming light gage wires with some resistance.
You need to use heavy cables with "zero" resistance.

[Jon Vermilye]

Originally Posted by Wayne Collins

You are assuming light gage wires with some resistance.
You need to use heavy cables with "zero" resistance.

er, that would be superconductors!

[Raspy]

Originally Posted by Wayne Collins

You are assuming light gage wires with some resistance.
You need to use heavy cables with "zero" resistance.

I'm not assuming anything of the sort, I'm reporting test data on my house batteries with full sized cables. Can you show me a wire with "zero" resistance?

You're at two strikes. So far you've assumed I had bad connections and undersized wires without ever seeing the setup.

All I've done is report actual test data in a real life situation, with batteries I relied on all the time, and watched carefully, to power my home.

Oh, and by the way, this is the way Oliver wires their parallel groups too. They came to the same conclusion I did, but entirely separately. And we both went to the trouble to wire our systems in the same way. Because that's how you assure both batteries in a parallel group charge equally.

[redbarron55]

Actually you cannot be sure that the batteries charge the same unless they are perfectly matched. The split in current is dependent on the internal resistance of the batteries as well as the external.
To check the balance of charge you can check each cell's specific gravity and compare battery to battery.
The internal resistance is the voltage drop measured at the posts under load. If a battery had no internal resistance there would be no voltage drop at all.
The current will flow inversely proportional to the internal resistance.
This also depends on the state of charge of the battery as the charge increases the charge will drop off assuming the voltage remains the same. This effect will tend to equalize the batteries, but they will still behave differently, based on the internal resistance at any given time.

[John in Santa Cruz]

Originally Posted by Raspy

Whenever you charge two batteries in parallel, it's best to connect the charger's pos lead to one battery and the neg lead to the other battery. This will charge them with the same amount of current and they will reach the same state of charge. If you connect both leads to one battery, the second battery will get less.

you also should have the loads connected that way.

[Raspy]

Originally Posted by John in Santa Cruz

you also should have the loads connected that way.

Yes. Definitely.

[John in Santa Cruz]

for those who don't quite get what Raspy and I are saying.... pictures!



this way, each battery has the same amount of wiring in series with it. if both + and - were connected on the left, say, then the right battery would have additional resistance in the form of the bridging wires.