Charging RV Batteries With Generator for Dummies

[njfishing]

So I just bought a 3200 watt Firman generator for my 2014 Roo 21DK and I'm sort of clueless when it comes to electricity.

The main purpose for this generator will be for boondocking when no 30 Amp service is available. For the most part I will use it to recharge the RV batteries and once in a while, to run other AC appliances while it's running...

I have two 6 volt golf cart batteries wired in series and was debating plugging my 15 amp portable battery charger in the the AC supply on the generator and using it to charge the batteries since I read that's the fastest way since the onboard RV intverter/chargers and the generator battery chargers are usually slow as well since neither put out enough DC power to do the job quickly..

I wrote Firman to see what the out put of the DC battery charger was on the generator, I got this in return and I'm trying to understand it and could use some help...

Does this chart mean that when I have the economy switch off, and a load on the generator not exceeding 14.1 volts on the generator that the max battery charger out put on the generator for charging the batteries is 8.1 amps ?

Next question is if I use the portable charger which is 15 Amps I would assume it would charge faster?

Can someone please help a dummie out

Thanks

[ependydad]

I've always been under the impression that the fastest charger is going to be the one built into the RV. They're typically 40-60 amp chargers.

That DC charger seems very slow at 8 amps.

I know my built-in one will push a good 30 amps to the batteries (I've seen it recorded on my Victron BMV app).

[njfishing]

Originally Posted by ependydad

I've always been under the impression that the fastest charger is going to be the one built into the RV. They're typically 40-60 amp chargers.

That DC charger seems very slow at 8 amps.

I know my built-in one will push a good 30 amps to the batteries (I've seen it recorded on my Victron BMV app).

Thanks for that Dad, the Firman does have a 30 amp output plug on it and it would be very convenient to plug the trailer into it and not to have bring and to hook up the portable battery charger.

[ependydad]

Originally Posted by njfishing

Thanks for that Dad, the Firman does have a 30 amp output plug on it and it would be very convenient to plug the trailer into it and not to have bring and to hook up the portable battery charger.

Just make sure that 30amp plug is 120v and not 220v.

Otherwise, that's all that I would do.

[bikendan]

nj, for the 10 years we owned our Roo, we simply plugged the shore cord into the generator and let the converter do the charging.
Never needed a separate battery charger and still doing it the same way, with our TracerAir TT.

[Flybob]

The on board converter will charge better and faster than either your stand alone charger or the 12VDC plug on the generator.

[aeblank]

If you want to go nuts, upgrade the converter and/or the wires to the battery.

[CHICKDOE]

plug shore power cord directly into generator. as mentioned earlier ensure that the 30 amp outlet on the generator is 120 vac, not 220 vac. test this at home to make sure you can connect to the generator. it is possible you may need an adapter. also if you have a EMS system in your shore power cord you may need a grounding plug for the generator. get this all worked out at home. but once you are connected to the generator you should be able to operate just like you were connected to a 30 amp shore power pedestal.

[ScottBrownstein]

Plug directly into the generator and let your converter do the work. From what I can tell, the 3 prong plug on a Firman is labelled RV and is a standard 30 amp/120 volt RV connector.https://www.costco.com/Firman-2900W-...100367440.html

[Mad Cow]

the converters in RV's are essentially a joke. If one really is interested in multi phase charging of batts via a generator, get a good multi phase batter charger.

While a converter will eventually charge batts, it is woefully inefficient. There is no way a converter is actually sending 50-60 amp down the line to the batts, and even if it were, it is highly inefficient. it is battery charging on the cheap for the manufacturer to get by with low cost. It is essentially a trickle charger. A good battery charger does far more than any converter can do.... repair, maintain, charge, float, recovery, even work for dual purpose, deep cycle, and Lithium batts.

For proper charging, you need a good charger. Something like a Xantrex or NOCO.

https://no.co/g26000

[ScottBrownstein]

Originally Posted by Mad Cow

the converters in RV's are essentially a joke. If one really is interested in multi phase charging of batts via a generator, get a good multi phase batter charger....

https://no.co/g26000

Most RVs come with Progressive Dynamics multi stage smart computer controlled converters or WFCO multistage units. Have no idea what "multi phase" converters might be but a good PD converter is certainly not a "trickle charger." It will put out rated amperage if properly wired with heavy wire and will automatically switch between boost, normal and storage mode and even provides pulses of high voltage during storage mode to keep the electrolyte mixed. Rated amperage and inefficient? Won't even touch that.

In my experience they are more than adequate.

[bikendan]

Originally Posted by ScottBrownstein

Most RVs come with Progressive Dynamics multi stage smart computer controlled converters or WFCO multistage units.

The vast majority of RVs come with WFCO converters. Only higher priced units come with PD units, from the factory.

[ScottBrownstein]

Originally Posted by bikendan

The vast majority of RVs come with WFCO converters. Only higher priced units come with PD units, from the factory.

Maybe, but WFCO converters are 3 stage units as well and not trickle chargers. In fact, a trickle charger wouldn't have enough amperage to power the 12 volt needs of an RV anyway. Either way...the converter is the way to go.

[TitanMike]

Originally Posted by Mad Cow

the converters in RV's are essentially a joke. If one really is interested in multi phase charging of batts via a generator, get a good multi phase batter charger.

While a converter will eventually charge batts, it is woefully inefficient. There is no way a converter is actually sending 50-60 amp down the line to the batts, and even if it were, it is highly inefficient. it is battery charging on the cheap for the manufacturer to get by with low cost. It is essentially a trickle charger. A good battery charger does far more than any converter can do.... repair, maintain, charge, float, recovery, even work for dual purpose, deep cycle, and Lithium batts.

For proper charging, you need a good charger. Something like a Xantrex or NOCO.

https://no.co/g26000

Sorry, but you're off the mark on this.

Maybe 20 years ago converters were inadequate but today's units are almost always equipped with a "multi-phase" converter/charger.

Even the cheap WFCO models that come with most FR products have a Bulk, Absorbtion, and Float Mode. The more upscale converters like those from Progressive Dynamics will have a fourth mode for equalization but it's a weak one at only 14.4 volts while a true "battery equalizer" can use up to 16 volts.


For anyone who's bought an RV in the last few years has a Converter/Charger that is adequate for most needs since most "Campers" go from full hookup site to full hookup site rather than boondock.

For those that Boondock and want their batteries to charge faster, step one is to increase the wire size from Converter to Battery Bank. Failure to go into Bulk mode is usually not the fault of the Converter but the voltage drop across the small wire (usually #8) the factory installs and it falsely tells the converter's control board that the voltage is higher than it is at the battery and it then switches to the slower Absorbtion rate.

FWIW, battery charger/maintainers that claim over a half dozen "Modes" are fluffing up the facts. They're counting meaningless features like sensing whether or not you have a 6v or 12v battery. They also have a "test" mode which is just an idle period that they check the voltage than light up some lights telling you what state of charge the battery is supposedly at. Essentially they all have only four modes, Bulk, Absorbtion, Float, and Equalization.

The rest is just Marketing and if you put it on your tomatoes they'll grow to the size of Basketballs

Before I changed to LiFePo batteries and was still using a 60 amp PD converter I regularly saw 30-40 amp charge rates initially. It's a normal characteristic of Lead Acid batteries to have the charge taper off as the internal resistance (impedance) rises so many think their converter is inadequate when it's just doing what's normal with lead acid batteries.

For people new to charging batteries with Generators, think simple. Just plug into the Generator just as if it was the power post in a campground. Most either have a 30 amp RV type receptacle built in or have an adapter available for the twist lock receptacle some use if they are a 120/240 volt model. Not many sold today that are like that as the RV market has grown so much.

[kcmusa]

In My case I have metered the on board charger. It does great when at bulk charge. but as TitalMike says my wire size must be stopping the charger from finishing the charge. after a bit a do switch to a standalone charger that fully charges my batteries. I do turn off the internal charger before i do this.

[ScottBrownstein]

Originally Posted by kcmusa

In My case I have metered the on board charger. It does great when at bulk charge. but as TitalMike says my wire size must be stopping the charger from finishing the charge. after a bit a do switch to a standalone charger that fully charges my batteries. I do turn off the internal charger before i do this.

You are right on the money there. My Georgetown 335 has about a 33 foot round trip of #8 wire. Even though I have a 70 amp Progressive Dynamics converter, I only average about 20 amps during a 4 hour "boost charge" cycle. I have been tempted to up the wire gauge but have never gotten around to it.

In addition, when the PD drops out of boost and goes to normal, it takes a long time to get the rest of the way to 100% with around 60 AH.

That drop out of boost is the PD's timed boost cycle with a charge wizard which is advertised to be 4 hours...and 4 hours it is!

Numbers are from my Trimetric data logger.