Charging House Battery With Generator and Battery Charger

[wstuart]

We have been boondocking for 4 days at a time, then head to RV park to refill, dump, laundry etc.  The question I have is can I run the battery charger at the same time we run the Generator.  We normally run the genny for about an hour in the morning to do coffee, and breakfast while the batteries are charging.  We dont us much power at night just a few LED lights, propane fridge, and whatever else automatically runs.
My charger has 3 settings, 2 /12 / 75 amps.  Can I use the 75 amp, it does say "starting"
I dont have anything fancy to tell me how much the batteries are charged I just go by the dumb lights on the panel.
What are your thoughts?

Cheers

 

[Old Bounder]

You don't want to run your external charger at 75amps in an attempt to get a much quicker charge during your short generator run time.  In fact, you probably can't force it to stay in that mode more than a few seconds/minutes, as this is meant just for a quick charge start of a vehicle with a very low battery.  Your batteries, NOT the charging source, (converter or external charger) will determine how much charging current is absorbed by the batteries. 

You might gain some charging efficiencies by upgrading to a larger converter/charger in your rig.  What make and model are you currently (no pun intended) using? 

Adding additional chargers for simultaneous charging is seldom effective, especially if one, or both, are considered smart chargers.

Others will be along shortly to dispute or expand on these comments in great detail.

 

[Gary RV_Wizard]

I agree with Lou on all counts. The 75 amp setting on your external charger is not 100% duty cycle - it just gives a quick jolt at 75 amps and then rests awhile before giving another. And I can almost guarantee the 12 amps (which is continuous) is less than what your RV's house charging system puts out anyway. Still, it doesn't hurt to have the external charger running at the same time. But it probably doesn't help a whole bunch either.

Are you aware that your RV's own charging system is operating anytime the generator is on? You probably don't need an extra charger unless the house system is really puny.

 

[wstuart]

This is the write up on my converter

The WF-8900 Series has revolutionized RV power centers with its lighter weight, decorative doors, and superior features. The WF-8945 model provides 45 amps and a clean, constant 13.6 Vdc nominal output, for reliable operation of electronics and appliances. Automatic three-stage charging extends the life of your battery with output voltage modes of 13.2 Vdc ?float? mode, 13.6 Vdc ?absorption? mode, and a 14.4 Vdc ?bulk? charge mode. The 8900 Series also maintains peace and quiet, as the cooling fan runs only when needed.


Output Power  45 amps DC output

Input            105-130 VAC, 60 Hz (780 watt)

Output Ranges 
- Nominal (Absorption Mode) 13.6 Vdc (includes charging and load)
- Boost (Bulk Mode) 14.4 Vdc
- Trickle (Float Mode) 13.2 Vdc (after 48 hrs.)

I take it that means when required it will charge at 45 amps.  Now I check my 2 6 volt Trojan 105 for water every 2 weeks or so.  Need to add a bit of water about once a month.
Before reading on this site, I would check maybe every 6-8 months.  then add a bunch of water.

Cheers!

 

[Gary RV_Wizard]

Right - the theoretical max output is 45 amps, though it is doubtful if it could ever achieve that with an actual battery tied in. But even if it "only" does 35 amps with your battery bank, that is still a pretty decent charge rate when it is probably replacing something like 100-120 amp-hours. I would guess 2-3 hours would get the batteries back to around 80% of full charge. The remaining 20% would take quite a while longer because the rate will have slowed dramatically, maybe as low as 5-7 amps/hour.

 

[JerArdra]

I was once told that if you put two chargers on the same battery that the one with the highest voltage would be doing ALL the charging and the other one with the lower voltage would be doing NO charging.

What say you folks??

JerryF

 

[Old Bounder]

I was once told that if you put two chargers on the same battery that the one with the highest voltage would be doing ALL the charging and the other one with the lower voltage would be doing NO charging.
What say you folks??JerryF

Well Jerry, now you've been told twice.... LOL 
But, that doesn't make it fact.  Actually, I'm guessing. (guessing means that I haven't put it to a test)
I'm anxious to hear what the experts have to say on the subject.

 

[Lou Schneider]

In a perfect world, yes - the charger with the higher output voltage will charge the battery and the lower voltage charger will shut down.  But things are seldom perfect.

In reality, most chargers lose a little voltage as they supply more current.  Adding a second charger will increase the voltage at the battery terminals by lessening the load on each charger, but not enough to completely shut out the other.  More voltage at the terminals means more charging current is flowing into the battery.  The amount of voltage and current improvement depends on the Voltage vs. Current curve of each of the chargers, so the difference can range from hardly noticeable to significant.

The current contributed by each multiple charger will be less than if it was connected to the battery by itself, but the total charging current will likely increase.

 

[JerArdra]

Lou,

Thanks for the answer.  If a person had an Onan 8,000 watt generator and a Honda 2,000 watt generator both connected I suppose that the much more powerful Onan would most likely shut out the Honda.

JerryF

 

[Lou Schneider]

No, no, no, Jerry!

You can connect multiple DC sources in parallel to get more current.

But you can only use one AC source at a time.  That's why we have transfer switches. Multiple AC sources look like dead shorts to each other, unless you use sophisticated synchronization and balancing techniques.

The Honda inverter generators will synchronize themselves, which is why paralleling two identical Hondas is the exception to the rule.  But you can't parallel an EU1000i with an EU2000i.  Or a Honda to any Onan.

But I suspect you already know that .... 

 

[dirko]

Hi Ho:  Actually, connecting two ac generators is much more problematic.  The problem is that they have to have the same phase (which of course they don't) in order to supply the same line.  What happens is that there is usually (hopefully) breakers involved that will trip if you try that.  If not, they force one another into the same frequency/phase.  This is akin to bringing a generator online on the power grid.  It is done very carefully by making sure they are in sync first then making the connection.  If they are not synchronized you get a mighty bang and generator windings sometimes fly apart as the rotating armatures are forced to sync.  By the way, this is not an experiment for the casual observer.

 

[Gary RV_Wizard]

Jerry, In nearly all RVs, the generators are not doing the charging at all - they merely provide 120v power to the charger built into the RV. Multiple generators does nothing and in fact cannot be used simultaneously for the reasons Lou outlined.

Some small portable generators do have a  separate 12v output and can be used as a charger, but the big Onan 8000 is strictly a 120v unit.