charging batteries with generator

[seahunter]

Still confused on this, and VERY green - never had a generator OR even used a battery charger. From what I understand it is not efficient to charge the trailer batteries just running the generator. Don't have the unit yet, but is there a 110v outlet on the Onan generator? Or, would I just use the 110 outlet in the basement? If so, is this the most efficient method to charge the batteries by using a battery charger? If so, I will have two six-volt batteries. Do I just need to figure out which one is going to the house and attach the charger to the other battery?

Thanks much for any help!

Greg

[trfield58]

Greg,
I'm certainly no expert on the topic of batteries and charging but I'll attempt to answer your question based on what I have learned. It's considered inefficient to charge the batteries with the generator (either plugging in a portable unit to the coach input, or if you have a unit installed in the front compartment) because the batteries are charged by the convertor. That method will apply somewhere around 8 to 9 amps and up to 14.5 volts. The problem is, it will take several hours to fully charge the batteries (up to 12 hours) and if you factor in the cost of the gas or propane needed to run the generator = NOT EFFICIENT. If you are running the generator for 12 hours to supply AC power to the coach for other uses anyhow, then that's more efficient because you are using AC power AND charging the batteries. In a nutshell, just running your Onan generator to FULLY charge your batteries only uses a fraction of the output of the generator and you will go through a lot of propane. I have a 3000W Kipor and if all I want to do is charge, I connect an automotive type charger (30 Amp) to my batteries for 3 or 4 hours. Again, I'm not an expert so by all means do some additional research.

Good Luck,
Tim

[Ishler]

As I remember the converter documentation and a presentation from the fall rally year before last, it says the converter will charge up to 40 or more amps depending on what stage it's in. Basically any capacity that is not going to the rest of the trailer goes to the battery in the first charging stage. The current then drops depending on what stage it's in.

[Joel and Julie]

Our 2010 Montana 2955RL has an inteli Power PD9280 charger. According to the manual, this charger puts out 14.4 volts and up to 80 amps until the battery is 90% charged. At that point the charger drops to 13.6 volts.

I've been told that older Montanas (and many other brands) only put out a continuous 13.6V. This will result in battery charge times measured in tens of hours.

[trfield58]

Yes, I should have looked at the model year. The new convertor/chargers are WAY better than the older ones. It's still a question of the efficiency of running an Onan LP generator to charge batteries...???? My thoughts are; if you are running the generator just to charge, probably not efficient because the LP generators really like the fuel.

[seahunter]

Thanks for the responses! To add to my original post, the reason I would be charging the batteries would be a boondocking situation where the batteries needed to be charged, with the generator being the only option, but whether to use a seperate battery charger.

Thanks again!

Greg

[hookman]

You could also hook up a solar charger for when you are away or just not running the gen set.

[2 for Him]

Greg,
1st: The 2 six volt batteries in your rig are hooked in series for the 12v system in your Monty. Charge them both at the same time with a 12 volt charger. Try not to take your batteries below half charge, they lose up to half their lifetime when run completely down.
2d: The converter is only less efficient over the 90% SOC (State Of Charge-- you may as well learn all the lingo) or whenever it goes into absorb mode, the manual stand alone battery charger will keep it's voltage higher and thus charge fractionally faster. A battery has an internal resistance which raises as the SOC climbs, slowing the ability of any charger to finish the charge.
3rd: The newer chargers have at least 3 rates of charge for a reason (my solar controller has 6), fast charging a battery for the last part of the charge is hard on the life expectancy. By the way, most boondockers try for a 50-90% SOC cycle to comprimise between battery life and generator use, then get a full 100% as often as possible.
4th: Conservation is way more cost effective than any mode of charging. Changing to LED lights will dramatically improve your battery time, turning off anything not in use, using a small inverter for small loads, ect. I was going to put in a large inverter for the micro and hair dryers, then realized I had to start the generator regularly anyway to excercise it, so I wasn't accomplishing anything.
5th: If you want to get OCD about it (DW says I am) get a battery monitor to keep track of your SOC, amps and amp hours in and out of the battery, volts in and out, dime to discharge at current useage, when to recharge and lots more.
Here is even more information that you probably don't want or need.
http://windsun.com/Batteries/Battery_FAQ.htm
Most of all, relax and have fun, the world will still keep turning if you get a low battery.
By the way the 8-9 amps from your converter info is about 20 years out of date. I have always had an ammeter on all mine and even 10 year old ones will put out their full rating if the battery will take it.
Tom

[seahunter]

quote:Originally posted by 2 for Him

Greg,
1st: The 2 six volt batteries in your rig are hooked in series for the 12v system in your Monty. Charge them both at the same time with a 12 volt charger. Try not to take your batteries below half charge, they lose up to half their lifetime when run completely down.
2d: The converter is only less efficient over the 90% SOC (State Of Charge-- you may as well learn all the lingo) or whenever it goes into absorb mode, the manual stand alone battery charger will keep it's voltage higher and thus charge fractionally faster. A battery has an internal resistance which raises as the SOC climbs, slowing the ability of any charger to finish the charge.
3rd: The newer chargers have at least 3 rates of charge for a reason (my solar controller has 6), fast charging a battery for the last part of the charge is hard on the life expectancy. By the way, most boondockers try for a 50-90% SOC cycle to comprimise between battery life and generator use, then get a full 100% as often as possible.
4th: Conservation is way more cost effective than any mode of charging. Changing to LED lights will dramatically improve your battery time, turning off anything not in use, using a small inverter for small loads, ect. I was going to put in a large inverter for the micro and hair dryers, then realized I had to start the generator regularly anyway to excercise it, so I wasn't accomplishing anything.
5th: If you want to get OCD about it (DW says I am) get a battery monitor to keep track of your SOC, amps and amp hours in and out of the battery, volts in and out, dime to discharge at current useage, when to recharge and lots more.
Here is even more information that you probably don't want or need.
http://windsun.com/Batteries/Battery_FAQ.htm
Most of all, relax and have fun, the world will still keep turning if you get a low battery.
By the way the 8-9 amps from your converter info is about 20 years out of date. I have always had an ammeter on all mine and even 10 year old ones will put out their full rating if the battery will take it.
Tom

Tom,

Thanks so much for the thorough reply! I had thought about the need to excercise the generator too, so maybe this is a good way to charge the batteries once in a while. Sounds like I can do it without a seperate charger then. I couldn't find any info on the charger in the Montana, so that's good to know they are better than they used to be.

Conservation is definitely going to be an issue for us. Both myself and Mrs. Seahunter both use CPAPs. When we used to camp, it was just me on the CPAP, but now we will both be sucking down the batteries with them. I like the LED light idea, will check into that.

I probably will be OCD on it LOL... I looked at a Xantrex battery monitor that looked really good and will probably be an early add-on.

Thanks for that link too, great info.

Greg

[seahunter]

By the way, I love your shirt in your avatar "Will work for diesel".
Good stuff.

[Joel and Julie]

Another rule of thumb to keep in mind is that even at the full 14.4V charge voltage a battery will only charge about 10% of it's capacity per hour. The 80A charger I mentioned previously would only charge at 80A if I had an 800 Amp-Hour battery bank. Golf cart batteries are around 200 Amp-Hours,which means about 20A continuous charging.

The manual that came with my Montana charger shows a charging diagram that's pretty linear and hits 90% charge at 8 hours. This is for a battery starting at 10.5 Volts (which is quite discharged).