Elec help needed to charge house batteries

[John Z]

As part of my prep for my first long trip with my bus, i was working with the house bank. I installed a digital display hooked to both the house and bus/start batteries. While watching the display, i have discovered that the house batteries are not getting charged while driving!

I am leaving either Fri or Sat, and i would like to get the house batteries taking a charge while OTR. My bus is sitting outside, and it is not supposed to get above zero for another 3 or 4 days, so i can't do anything to elaborate.

I have searched for the answer to this problem and read the archives at the other board, and read different web sites. While they all give good info and theory etc, not one of them gives a diagram showing how to hook up the needed equipment to handle this.

Is there a diagram anywhere showing what wire to take from the generator (or where ever i start from) and how to wire in a isolator or solenoid? Can you tell i am not an electrician? I can do the work, if i just know what to do.

My brother gave me a Sure Power isolator, but it is rated for only 70 amps max. Can this be used to control charging the house battery, or is it too small? If it is useable, where do i get the wire to attach as input to the isolator. This is on a 4104, neg ground.

I will greatly appreciate any help,,, even if it is only a tip on how to "hot wire" the house battery while driving to get it charged. I just can't get it into my head how the bus generator can know when the house battery is fully charged etc, and cut off the supply.

I just checked the temp outside, it is -22.2 F and still falling, so as i said, my outside time available for working on the bus is short. Thanks for any tips or advice.

[rdbishop]

Hey John Z . Till you can find out how they normally get charged, You could start the bus and then hook up a set of jumper cables between house and start batteries.

[John Z]

Not a bad idea,,, the distance is too far for jumpers (house batteries are way up front), but perhaps a run of 12 ga romex? Do you think that would that work?

[rdbishop]

The romex will work as long as you don"t have big load on the house batt.

[John Z]

Thanks. It should be ok to get by with then,, only running some fans, a couple lights, stereo, and the big draw is the furnace fan, but i usually shut that off while otr and just use the ceramic htr. Thanks again for the suggestion.

[rdbishop]

Boy,I sure hope your going someplace warmer. It"s going to get cold here in S.A


Boy, I sure hope your going someplace warmer!

[John Z]

Yep, thats the plan,,, head south! First fuel stop will be at 600 miles at Kansas City, MO. From there we will take off toward Ark, but be chking the weather forecasts to see where it is warm! Maybe Louisiana, maybe TX. Would like to swing through KY and TN if it works out to. I am just sick of the cold winters, and this is my second to last one i will spend here. Bringing the bicycles, and am really looking forward to putting some miles on them.

Where is S.A? BTW, just chked and it is -24.3 F and still dropping!!! Man that sucks!

[Jeremy]

Small point, but before you go connecting jump leads or cables are you sure the house batteries and start batteries are even the same voltage? They often aren't. Apologies if this basic question seems insulting but better to make sure you have checked than have you damage your batteries and maybe yourself

Jeremy

[Tom Y]

Do NOT run 12/2 romex without putting fuses in the line. 20 amp max. I am building mine and it looks like yours,  a continious duty soliniod to tie the coach and house batteries together. I am controling it with a oil presure N.O. contact. This will not be heavy enough to tie the batteries together to start the engine if it is dead. I put a MCI disconnect between them for this. Make sure of the voltage of both banks. 12 volt coach? 24 Volt start? Where are you located at? There may be someone near by to help. I like looking at others buses.  Goodluck Tom Y

[Tom Y]

Sorry guys. I meant the post above  to go to LeagalEagles postl  Tom Y

[Ross]

Charging a house bank from the start bank with a 12ga wire?  What am I missing?  If it has a high amp alternator, like an MCI (270A) then the current going through that charge wire could be as high as that.  I'm probably missing a piece of the puzzle.  I know you guys wouldn't suggest connecting two battery banks with a 12ga wire.

The connecting cable should be at least 2/0, bigger if it's a long run.  The solenoid needs to be rated for a least what the alternator puts out, which is probably alot more than 70A.  For a simple charge system, you can just run a charge cable from the start batteries to a manual battery switch then to the house batteries.  After you start the bus, turn on the switch.  The solenoid does the same thing, just automatically.

Ross

[John Z]

OK Ross, so your saying i can just run a piece of 2/0 wire between the positive posts of the bus battery bank and the house battery bank, with a switch in between? Sounds simple enough. Yes, both banks are 12v. Would it be worth the extra length of cable to bring it into the driver compartment with the disconnect switch? Or should i just leave the cable as short as possible? Bus bank is in rearmost bay drover side, and house bank is is bay right behind front axle driver side, so the driver panel is right above the house bank.

[gumpy]

I wouldn't bring that large wire and switch into the driver's area.

I used a 200 amp relay to connect mine. Works well. I'd recommend you do it that way. Then you can put the switch in the driver's area.

If you don't get it by the time you leave, you're welcome to drop by on the way past the cities (not too far out of your way) and I'll help you get it figured out. Unfortunately I don't have a shop to pull it into but I've worked in the cold before. We could make it work.

Do you have a relay? 

If you need a switch, or a fuse/holder, I may have it here, of I can get it from Waytek in Chanhassan. Might be able to get a relay from Grainger in Plymouth, too, if you don't have one.

[John Z]

Craig, that is an incredible offer! Thank you very much, but i would hate to drag you out in the cold so early on a Sat morning. But using your advice i know what i need to do and will try to track down those parts. I like your idea about the relay. I believe there is a Grainger in Duluth, if not, i know there is a Graybar that should have them. I may not get it all hooked up before i leave, but it will give me something to do when i get somewhere warmer, while the brats are cooking! I sure would like to see your bus,,, i still remember the pics you sent me about the pex fittings. It looks like you are doing one hell of a job on it! Maybe it will be warmer on our next time through. Thanks again.

[DrivingMissLazy]

I think the size of the relay depends on the size of the house battery bank, not on the size of the alternator.
On DML I had four 8-D batteries. Although I had a 150 amp capacity charger, the most amps I ever saw the charger putting out was about 70-75. This was when I had run the batteries down pretty low. Generally it was in the 40-50 amp range. I personally believe the 70 amp isolator he has is adequate unless the battery bank is significantly larger than four 8-D's, and the wire would not need to be larger than six guage.

Many people make the mistake of calculating the charge circuit components based on the capacity of the alternator. It really needs to be based on the capacity of the battery to take a charge at the highest acceptance rate without boiling the battery.

Although it may exist, I have never seen a house battery bank capable of accepting a 200 amp charge.
Richard