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Old 05-07-2015, 06:08 AM   #1
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Default Truck alternator charging house batteries

I have a question about using the alternator to charge house batteries while driving or running the engine. I have a 2004 renegade with the Mercedes 450/12spd. I am wanting to run a jumper wire from my truck batteries to the house batteries.,I am wanting to hook it to a switch so it can be shut off. I think it would be handy to have if you ran down the house batteries, you could use it to start the generator or vice versa to jump off the truck if e truck batteries get weak.

I have a master shut off switch for the truck batteries just inside the door under the driver seat and would mount another just like it for between the truck and house batteries. Do you think the alternator could handle this? I would use 1/0 wire to handle the load.

Thanks
Eric
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Old 05-07-2015, 11:28 AM   #2
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I've been using the Magnum smart battery combiner ME-SBC. It's fully automatic so
you can set the cut off point so you don't drain them both down. I set the low cut
off so when it isn't charging it's separate. This way while driving it's charging both
or when plugged in the charging of the house batteries charges the starting batteries.
It will transfer 25A so the wiring isn't that heavy. This won't charge things the fastest
but shouldn't overload anything.

On a separate note I have our generator tied into the starting batteries so it is easy
to start even if the house batteries are low. That was always a challenge to start
our generator in our 5th wheel when the batteries were low. Now I never have to
worry about our house batteries being so low that we can't start the generator.
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Old 05-07-2015, 12:52 PM   #3
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Eric -

Welcome back.

My (ok really my wifes) coach has exactly what you speak of - a generator emergency start switch that (momentarily) combines the house batteries to the chassis batteries, in case where the house batteries are dead & cant start the gen.

My coaches engine / alternator charges the house batteries going down the road....i know this because i installed 20 bucks worth of panel meters & i can see the house battery voltage INCREASE when the coach engine is running.

I carry a set of heavy jumper cables with me - if i ever needed a jump and the over ride switch / relay isn't working i can just use the jumper cables to manually combine the battery sets.

Im not sure you really have to do anything to get what you desire - its all there on my coach now (from the factory).

HOWEVER....because of a relay....the the generator only charges the HOUSE batteries when its running, not the coach batts too.

Panel meters...get ya some

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Old 05-07-2015, 01:39 PM   #4
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Amazon 12vdc Panel Meters HERE

Amazon 120vac combination Volt / Amp Meters HERE

the AC panel meters are easy since they have an inductive current/amp pick up...all you have to do is slip the inductive pick up over one of your AC Volt hot leads and you're good to go...if you have 50a (like i do) you'll want TWO meters (one for each 120v 50a leg) so you can monitor both legs.

you can see the inductive pick up in these pictures
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Old 05-08-2015, 09:19 AM   #5
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Hi Eric, like Don says, you might already have it able to do what you want. I bought my rig used off a lot and the salesman did a great job teaching me about how everything works. After owning for awhile I figured out that the truck engine wasn't charging the house batteries. There is a large round switch in my battery compartment that controls which battery bank is fed into the living quarters electrical system (12 volt that is). I thought when I had it set for both sets of batteries (chassis and living quarters) it would then charge the house batteries when the engine was running. It wasn't working that way. I called the factory that built it and talked to a guy. I was lucky I called before they went out of business in '09. He told me they have a switch on the dash that needs to be turned on to allow the house batteries to be charged by the engine. Huh? Never would have figured that out. I just leave that switch turned on now and it's all good.

I usually leave the large round switch in the compartment set for both sets of batteries when running down the road. Then when we're off the grid I set that switch to just the house batteries. That way I can use them up and not worry about being able to start the engine. My generator starts with the truck batteries, not the house batteries. I think that's the opposite of how Don's is set up.
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Old 05-08-2015, 10:54 AM   #6
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Our coach has TWO battery switches (on or off is the only setting, unfortunately there is no either or or combine option. the Off position terminates the flow to/from the batteries.

When I'm in storage i terminate the battery connection by switching the house batteries OFF. This also prevents the converter/charger from charging the HOUSE batts.

I run a separate battery maintainers (batteryminder) - one for the house batts & one for the chassis/engine battery.

I USED to terminate (turn off) my engine batteries when in storage - but i got tired of resetting the XM/Dash stereo programs....i just leave the engine batteries "ON" now & let the charger maintain the engine batteries.

There SHOULD be a Battery Isolation Relay (mine is in the house battery bay) - that relay allows the automatic combine of the engine/house batteries (when the engine/alternator is running & outputting 13.4v).

If you DONT have a battery isolation relay i suggest the BLUESEA (automatic) - I run the BlueSea relay on my F350 for a 3rd battery that i added (under the truck on the frame rail).
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Old 05-08-2015, 11:45 AM   #7
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BOB - makes me wonder....

Ive got a "option" switch on my dash that I've NEVER been able to figure out what its for....
its NOT for the engine fan, and damn if i can find anything that it operates.

Ive got another option switch on the dash that works some "reverse" lights on the coach, so its not that.
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Old 05-08-2015, 08:56 PM   #8
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I think my batteries are totally seperate. There is a battery kill switch under the driver seat for the truck and another near the batteries for the coach. If I shut off the truck switch then nothing works in the cab of the truck, generator running or not. So I think it is totally isolated. I have a set of jumper cables that I can use to start the generator if I run the coach batteries too low if needed. I just want to be able to run a small inverter for the tv, satellite, for the kids while driving. It's only a small 800watt cobra from a truck stop so it doesn't use much, I'd just like to have the truck charge the coach batteries while driving. In the summer it won't matter much because the generator will run the ac and everything else. I just like to not have to run the generator unless necessary.
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Old 05-08-2015, 09:02 PM   #9
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Quote:
Originally Posted by bushpilot View Post
BOB - makes me wonder....

Ive got a "option" switch on my dash that I've NEVER been able to figure out what its for....
its NOT for the engine fan, and damn if i can find anything that it operates.

Ive got another option switch on the dash that works some "reverse" lights on the coach, so its not that.
That's the switch United Specialties used on mine. It's down there on the lower left of the dash. I also have that extra backup light switch. The "option" switch is right next to that. I think if you are plugged in to shore power and stick a volt meter on the chassis batteries and see if that voltage matches the house battery voltage. Then switch that "option" switch and see if the voltage now matches the house battery voltage. That's how mine works anyhow.
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Old 05-09-2015, 08:36 AM   #10
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Quote:
Originally Posted by Bottomland4x4 View Post
I think my batteries are totally seperate. There is a battery kill switch under the driver seat for the truck and another near the batteries for the coach. If I shut off the truck switch then nothing works in the cab of the truck, generator running or not. So I think it is totally isolated. I have a set of jumper cables that I can use to start the generator if I run the coach batteries too low if needed. I just want to be able to run a small inverter for the tv, satellite, for the kids while driving. It's only a small 800watt cobra from a truck stop so it doesn't use much, I'd just like to have the truck charge the coach batteries while driving. In the summer it won't matter much because the generator will run the ac and everything else. I just like to not have to run the generator unless necessary.
EXACTLY how ours operates too - the Battery isolation relay (mounted near the house batteries) allows the charging of the house batteries by the engine alternator.

the on/off switches are close to the batteries (in the circuit design) so when you switch off the batteries it will kill everything in that circuit.

the generator's alternator ONLY changed the house batteries when the generator is running (regardless of the position of the engine battery switch) - i believe you would need another battery isolation relay for the generator to charge the coach/engine batteries.


Quote:
Originally Posted by Bob86ZZ4 View Post
That's the switch United Specialties used on mine. It's down there on the lower left of the dash. I also have that extra backup light switch. The "option" switch is right next to that. I think if you are plugged in to shore power and stick a volt meter on the chassis batteries and see if that voltage matches the house battery voltage. Then switch that "option" switch and see if the voltage now matches the house battery voltage. That's how mine works anyhow.
ill be checking that out, thanks !

fwiw i do have a "generator emergency start" switch thats mounted on the wall near my generator start/hour meter - I've never used or tested it but its function is to combine the coach engine batteries w/ the house batteries to start the generator (in the event that the gen batteries are dead).
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