Battery combiner

[chuckd]

My shorty Prevost has 5 8D batteries in 4 separate banks.  Two of the 8Ds are wired in parallel for starting the 6V-92.  They are only charged while running by the alternator.  I have 1 8D battery in bank A, and 1 8D in bank B for the house banks, and 1 8D for the gen set start.  They are charged underway by a 12 volt alternator, and while parked either by the gen set or shore power.  Since I park overnight in cold climates, and even though when parked I will have my engine heater plugged in, it might be nice to be able to parallel the two house banks together to add their cranking power to the start batteries.  Is there a switch/relay system to do this?

Thanks in advance
Chuck

[Jerry32]

There are many battery switches available to do this and it is handy to canect bak=nks together or seperate them. I heve three banks and a seperate switch for each one plus a sw to also add the start batteries to all. Jerry

[luvrbus]

That is going to be a tough one Chuck  your starting system is 24V and the house is 12v ? years ago Mack had a parallel switch that the batteries charged on 12V and converted over to 24V for starting I don't know if that would work or not maybe Sean or the other guys can help you with a design.  


good luck

[Van]

Clifford, Chuck, Sean I think covered this area in his recent article in the BCM article(April) titled House battery systems: 12 volts or 24?haven't had time myself to read it completely, but intend to, looks like a winner. V.

[luvrbus]

Van, it is easy to tie the banks together if the same voltage 50 bucks for a solenoid  but 12v to 24v for starting is going to take some planning the solar people do it but on a small scale 


good luck

[Rick 74 MC-8]

Chuck
           Check Kenworth. We had  a 80 maybe late 70 with a 8v92 and 24 v starter everything else was 12volt Heard a clunk when a solenoid changed system to 24v for starting That's all I remember


                                                                  Rick 74 MC-8

[luvrbus]

If my memory serves me today I believe the trucks used a postive ground when they had the 12V charging with 24V starting maybe not 



good luck

[Chopper Scott]

The parallel switches were a non stop problem and most trucking firms yanked the 24 volt starters and replaced them with 12 volt and eliminate the switches.

[Sean]

This is a non-trivial problem.  In order to "series" the two house batteries to boost the start batteries, you will need to first disconnect them completely from the house system (because both the ground connections as well as the positives will need to be broken), then re-connect them to the start batteries, then change it all back again.

The amount of current involved in starting an engine requires very large switches.  Double-throw relays in these DC amperages are very expensive, and also very large.  The difficulty involved in interconnecting house and chassis systems of different voltages is one of the key reasons I always recommend you use whatever voltage the chassis demands for your house system.

Yes, this can be done, and I can walk you through it if you want to spend the money (I estimate well over $700) and invest the hours (I estimate well over 40) in doing it.  But for my money, I would sign up for Coach-Net for $100 a year.  They'll come give you a jump any time you need it, and you'll get towing to boot.  You will be money ahead in the long run.

-Sean
http://OurOdyssey.BlogSpot.com

[Lin]

Since you mention having the block heater plugged in during these cold nights, I assume you have electricity.  Why not just add a multi-stage 24volt battery charger for your start batteries so they will be still topped off in the morning?  It would be good to have such a thing anyway for when the bus is not in use.

[NewbeeMC9]

Am I confused?  I am pretty sure he said the Start batteries are parallel which would mean he has a 12 volt Starter


If they were in Series he would have a 24Volt Starter.



You can use continuous duty high amp solenoid.,  but chuckd, do you have 2 alternators? or one,  they may be connected already.

[chuckd]

Whoops the start batteries are wired to produce 24 volts and are charged from their own 24 volt alternator.  Sean, after I posted I did a circuit diagram from what little I can remember from my EE courses and came to the conclusion that this was non-trivial, so will take advice of others and keep the batteries topped off with another charger.  (and I have roadcare service)

Thanks again

Chuck

[luvrbus]

Here you Chuck may not be a big deal after all www.texasindustrialelectric.com/relays_1119845.asp called a series parallel switch 


good luck

[Just Dallas]

Removed

[Sean]

Dallas,

Those drawings are hard to follow.  Once I muddled my way through them, I found them to be less than ideal.

Specifically, the system described relies on a single-throw switch being opened before the start solenoids are energized.  If that step is omitted, and the solenoids are energized, Solenoid 1 will immediately ground the positive terminal of battery 1, with possibly nasty results.  You could weld the solenoid shut and explode the battery in short order.  I see the only thing preventing disaster is the reliance on a fuse to blow in the event this happens.

To be completely safe and reliable, any such system should use a double-throw switch such that a direct short to ground could never occur.  And it is precisely the enormous expense of such a high-current, DPDT switch that made me suggest earlier that this is a non-trivial problem.

The system pictured is a "cheat" that works so long as a certain sequence is followed every time, but is not fail-safe and has a lot riding on the human element.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com