Can I charge batteries with a charger and generator?

[monicarick01]

I have an on-board generator and was wondering if it was possible to hook up a battery charger to the trailer, while the generator was running and use any "extra" power that the generator produced to help charge the batteries?? I have a smaller battery charger 12v/6amp.

thanks for looking

[mena661]

MEXICOWANDERER wrote:
then argue when a professional tries to educate them. Sad Sad Sad

It's one thing if the pro clearly doesn't know what he's talking about but the one's that do know (like yourself) get the same treatment. It irritates me to no end. From my point of view, people that know their stuff are EASY to spot but it seems the average person can't (or refuses to) see the difference.

[Ron3rd]

What if the OP hit the battery disconnect switch then put the batteries on a portable charger, powered by AC of course?

[MEXICOWANDERER]

Decorum Ninerbikes,

Decorum

The problem is we do not have a Federal Trade Commission anymore. Companies can peddle all the fraudulent garbage they want to, lie like hell, blatantly, full page ads, and the public swallows it and asks for seconds. If it is in print, or on a website, it MUST BE TRUE. Wotta hoot, here I am an aged engineer, and some people challenge me and say "What You Say Can Not Be Fact" After all they can link on some web page and prove me wrong. America has become a nation of suckers. The ones I fell sorry for are innocents who buy into the hucksterism, and those who I do not feel sorry for buy into the hucksterism, then argue when a professional tries to educate them. Sad Sad Sad

[NinerBikes]

MEXICOWANDERER wrote:
WILL


WORK

Just don't use an automatic charger. Look back through this thread and see the long post about the 33 amp power supply that is manual, works better than a transformer charger, does not lose potential like a transformer charger, and actually charges batteries in conjunction with a "s-m-a-r-t" charger.

Chargers with integral IC controls are turning many of you folks into victims. You believe what limitations these converters, impose on you is law. You are bent over with your pants down around your ankles with a sign on your back, saying KICK ME.

And you're pretty damn lucky if all the sign really says is KICK ME. It could and usually is a lot worse.

[MEXICOWANDERER]

WILL


WORK

Just don't use an automatic charger. Look back through this thread and see the long post about the 33 amp power supply that is manual, works better than a transformer charger, does not lose potential like a transformer charger, and actually charges batteries in conjunction with a "s-m-a-r-t" charger.

Chargers with integral IC controls are turning many of you folks into victims. You believe what limitations these converters, impose on you is law. You are bent over with your pants down around your ankles with a sign on your back, saying KICK ME.

[NinerBikes]

It depends on the brand and model of the charge controller, and the brand and model of the battery charger, and the voltage they each put out, as well as how smart or dumb, or manual they are.


My little stinking Sears Roebuck 6 amp 12 Volt battery charger that is manual is fully capable of putting out 16.0V. If I run my POS WFCO and the manual charger at the same time, the WFCO puts out nothing... it's forever trying to charge in float mode at 13.4 Volts. The manual charger overshadows it in voltage, so the manual charger does all the work and the WFCO does nothing. Which ever charger has the highest voltage will do most or all of the work in charging.

[NinerBikes]

double post

[mena661]

X2 BFL is the master of multiple chargers

[BFL13]

dbbls wrote:
Won't work. When your onboard generator is running your batteries will show full charge because the converter is putting power to them. A separate battery charger will read this as a fully charged battery and will not provide any power to the battery.

If that happens with that charger then all you do is turn off the converter (how to do that depends on the RV ) start the portable charger, then turn the converter on.

It depends on charging voltages whether they will add their amps and in what proportion. Say the charger can do 14.4 but the converter does 13.8 and the battery is at 12.2 at first. Also the battery must accept that many amps.

Both charger and converter will add their amps till battery voltage reaches 13.8 when the converter no longer contributes. Its amps will taper as battery voltage nears 13.8 then will stop as there is no more voltage spread. Meanwhile the charger will still be cranking out its amps to get the battery voltage to 14.4. Its amps will taper according to the charger's usual "charging profile"

If both have the same voltage, they share the amps all the way. Say the battery can accept 80a and you have two 40a chargers of same voltage. Each does 40a till battery acceptance drops below 80a then each charger's amps taper.

If one charger has slightly higher voltage then one will taper more than the other, so when battery will accept say 50a, one charger might be doing 30 and the other 20. It is proportional to the "spread" each charger has between its voltage and the rising battery voltage.

The generator needs enough watts to run all the chargers. Once one charger is doing/can do it all, you might as well turn off the other.
If two 40a chargers are each down to 20a, you can turn one off and the other will jump back to 40a and taper from there again.

[dbbls]

Won't work. When your onboard generator is running your batteries will show full charge because the converter is putting power to them. A separate battery charger will read this as a fully charged battery and will not provide any power to the battery.

[wa8yxm]

It depends on the trailers built in converter and the external charger.. There are several things that can happen.

1: They combine their efforts resulting in a faster re-charge
1B: this faster recharge may or may not be faster than the battery can be safely charged (Too fast shortens battery life) NOTE MAY or MAY NOT be, You got to do the addition and measurements.

2: Converter sees charger output and says 'Ok, full up" and goes into float mode

3: Charger sees converter and goes into float mode.


Bottom line is: Try it and see

using a good Clamp on DC ammeter, or a good Shunt Ammeter. measure charging current with just the converter, with the charger and with both, Compare to battery size and figure it out.

[pianotuna]

Hi,

So long as the charging voltage is under 15.4 you can leave the battery bank connected.

[tragusa3]

My memory is fuzzy, but I think the last time I checked voltages, charging with genny and just my outboard charger gave me the same charging voltage as using the trailer and outboard charger together? I thought the two together would increase voltage, but it didn't. Now, I don't understand electricity too well...maybe it did increase amperage and that's what counts?

A related question: Are you guys implying that I can charge my batteries with an outboard charger and leave the batteries connected to the trailer? I've been disconnecting every time I charge, and it would be nice to eliminate that step.

[pnichols]

To the OP ... yes it will work.

I often charge our RV's batteries faster when camping without hookups by using a generator to power both the RV's built-in converter and for powering a little inexpensive charger connected directly to the RV batteries' terminals. The currents from the converter and little extra charger do not directly "add up" however. Only part of the small charger's current capability gets added to the current that the converter is providing - not all the way up to what the small charger is capable of. So this technique does help some - but not dramatically.