keeping the generator start battery fully charged

[H3Jim]

Now that I have solar panels, I rarely use the generator.  I have a separate start battery (12 volt) for the generator.  All the rest of my system is 24 volt.  I'm looking for a good way to keep it charged without spending $60 for a Battery Tender. It seems with all my power sources (start, house, solar and power pole) I could find a way to keep it topped off.   I'd like to just wire something in and forget about it. 

The other issue with the Battery Tender is that it uses 120 volts, so I have to keep my inverter running.

what have others done?

[Stan]

Run one 8 or 10 gauge wire from the 12 volt terminal of your start batteries to the genset battery.

[H3Jim]

My concern is if the genset battery goes dead, or for some reason requires a lot of draw, that the resulting current would burn up the wire.

I do have 12 volts available from my house batteries as well.

I suppose I could just put a fuse on it.

[TomC]

Why do you need a separate 12v battery for your generator?  Just use the starting batteries.  If I remember right, if you hook up to the positive and negative of one battery only, you'll get only that batteries voltage even on a 24v system.  But-hopefully someone else can verify that.  Good Luck, TomC

[H3Jim]

If I was designing the system today, I'm not sure I would put it in, and especially now that I have solar.  I put the battery in when I first installed generator three years ago and didn't have much else in the coach.  Dick wright had suggested I have a "duplicate" battery so if the batteries went dead, I'd still have something to start the generator with.  Based on my previous experience with a 5th wheel, that had no other start batteries and the generator started from the house battery, I thought it sounded like a good idea at the time.

Now I pay such close attention to all my batteries, I doubt that I would be surprised by anything going dead on me.

The generator start battery is over 17 feet from the bus start batteries, and its probably cheaper at ths point to just buy a Battery Tender than to buy starting cables that long.

[Lee Bradley]

I would leave it the way it is and exercise the generator once a quarter. A good battery shouldn't have any problem holding a charge for three months.

[Nick Badame Refrig/ACC]

I don't know if you guy's know that the Dometic roof top Brisk Air and Penguins come with a option

of solar battery maintainers that intergrate with the dometic units.

They are equiped with a regulator to maintain a maxium of 14.1 volts and are covered by a 3 year warranty.

I'll post a pic.

Nick-

[DavidInWilmNC]

Now that I have solar panels, I rarely use the generator.  I have a separate start battery (12 volt) for the generator.  All the rest of my system is 24 volt.  I'm looking for a good way to keep it charged without spending $60 for a Battery Tender. It seems with all my power sources (start, house, solar and power pole) I could find a way to keep it topped off.   I'd like to just wire something in and forget about it. 

The other issue with the Battery Tender is that it uses 120 volts, so I have to keep my inverter running.

what have others done?

How about one of the 24 to 12 volt converters?  They're fairly cheap (on eBay, anyway).  You wouldn't need one with a large capacity... maybe an amp or two.

David

[Sojourner]

Whatever you do.......avoid tapping in anywhere between grd & pos posts of one or two battery in series (12v & 24v). All good battery's cells are to be equal state of charge at all time otherwise you will over charge the "already" charged ones.

Do what some already posted....second alternator, separate charger or solar power.
Never use voltage reducer from 24v source to charge separate 12v battery unless it same size battery & manufacture builds/installed same date & same state of charge as 24v battery bank.

Do what you want to spend over all...but the above is less trouble & cost in the long run.

Or run "Generator" every now & then.....to wet lubed, to check its performance and charge own battery. If its battery drain somewhat too soon....disconnect "Generator" own alternator's pos + terminal.....voltmeter at low scale range to connect in between alternator pos + lug and terminal end.....it should never be more than 1/2 volt drain otherwise bad diode or diodes in alternator.

FWIW

Sojourn for Christ, Jerry

[gus]

My old Onan gen required a separate gen battery because there was a small 12v DC alt built into the flywheel and wiithout a separate batt the alt would be destroyed. I used a lawnmower battery which was very small and sometimes was pretty weak.

To resolve this problem I installed a solenoid at the gen battery which was also connected to the eng start battery and  a toggle switch near the driver. Anytime my gen battery was kind of wimpy I would hit this switch and it would bring my eng start battery into the system and spin the gen as much as I needed. The gen battery would then be recharged in a couple of hours, or, if the gen wasn't used that long I would keep using the boost.

[Hartley]

If you already have solar, just tap into the first solar panel ( from ground ) and add a small solar charge module
to get the 12 volts to keep the generator battery charged. This way you don't have to change anything else
and the small independent solar charger can give the battery it's 1 to 2 amp maintainer.

Or just get one of the small 10 to 15 watt panels and glue it down somewhere convenient.

[Stan]

Sojpurner: Your advice to not tap between batteries is correct if you are drawing significant load. As an MCI owner, you must know that for more than twenty years, MCI ran their 12 volt entertainment systems of a 12 volt tap. The #10 wire was a standard part of the wire harness. The current needed to maintain the charge in the small genset starting battery will have little effect on the 8D engine start battery although its life expectancy may be reduced by a day or two.

[H3Jim]

Thanks for the input. While I wanted to not have to use the inverter and its losses to charge, I also wanted to keep the battery systems isolated so there would not be the possibility of massive current draws in either direction.  My solar, house and start batteries are all 24 volt.  I do have a voltage divider so I can draw 12 volts from my house bank without taking from only one of the batteries.

I do have a small current draw on the generator, I'm not sure where its going, but its enough that after a month, the generator start battery is getting low.

I have a 120 volt outlet near the generator start battery, so I decided to just spend $30 and get a smart trickle charger for it. Its cheap, easy and totally isolates the battery systems.