Multiple 24V alternators. Do or Don't?

[Tenor]

Here's the story.  Several years ago my 50DN died.  Put in a crank driven internally regulated 130A Leece Neville.

I just re-installed a new 50DN to run my Xantrex SW4054 inverter and 2 roof airs.

I have 2 gp 31 start batts by the engine with a master disconnect.  I also have 4 (soon to be golf cart batts for the house.  These also have a master disconnect from the bus chassis.  They are located in the original battery trays by the fuel tank. (MCI 7)

I have used the 130A alternator to charge both sets of batteries while driving with no issue, and am using the original wiring harness to connect the batteries.

With the return of the 50DN, what is the best way to wire it in to charge the house batteries without causing problems with the other alternator and start batteries? 

Thanks!

Should I connect the 50DN regulator directly to the house bank?  If so, what happens if the house bank is disconnected from the bus chassis?  would the alternator go to maximum output?

[Lee Bradley]

I not sure what you mean by  "what happens if the house bank is disconnected from the bus chassis?"
The alternator must always be connected to a load or bad things happen.
I would keep the 130amp supplying the chassis load with the 50DN powering the house batteries and the inverter with a switch to connect the
two battery banks for starting or if you lose an alternator you can power both systems from the remaining alternator.

[Tenor]

Let's take out the line "If so, what happens if the house bank is disconnected from the bus chassis?  would the alternator go to maximum output?" and forget I said it.  It was silly. 

[Zeroclearance]

Balmar MC 624 multi stage regulator.

[Tenor]

Zeroclearance,
That's a cool regulator!  Can't afford that right now, but it will go on the shopping list. 

Still, would it conflict with the other alternator?

[Sean]

FWIW, I agree with Lee.  Use the smaller alternator for the chassis systems and the larger one for the house, and keep the systems separate unless there is a problem (need a jump-start, or one alternator craps out).

When two alternators charge the same system, without a coordinating regulator such as the Balmar that was already mentioned, they will get into a race condition where one or both of the alternators are cutting in and out.  Not only is this not the most efficient way to charge, but it can wreak havoc with your tachometer, blower circuit, etc. and can increase alternator stress.  That said, nothing catastrophic will happen, either.

-Sean
http://OurOdyssey.BlogSpot.com

[Tenor]

I agree with Lee also, but the question is how.  Both alternators are tied to the bus wiring harness.  I can disconnect both sets of batteries from the bus wiring harness manually, but that doesn't make any sense.  Unless I made a relay that disconnects the start batteries from the chassis once the bus is started.  Then the 50DN charges the house system and runs the bus systems.

In reading the specs on the Balmar regulator, I didn't see how it would work with a second alternator.  Perhaps I missed it. 

Otherwise, I could direct connect the 50DN to the house batteries, but that would require about 25ft of 0000 wire.  They don't exactly give that stuff away! 

I don't have a tach, or blower circuit any more, but I don't want alternator stress or fried batteries!  Sure do appreciate the help Sean!

Glenn

[buswarrior]

The missing bits for the silent viewers:

To take full advantage of the big 50DN alternator to charge the house battery bank, a busnut would want to change out the stock voltage regulator for a 3 or 4 stage modern regulator in order charge the big house bank faster and more completely. The stock voltage regulators were fine for maintaining start batteries in seated coaches, but they don't do as good a job charging heavily depleted deep cycle batteries in a bus conversion after a night of silent sleeping, drawing them down.

Start batteries and the deep cycle house batteries require different charging strategies. Having one alternator do both, means compromise, and as we've learned, a battery that has its charging compromised, fails earlier, and that costs money.

Dedicating a smaller alternator to the start batteries and "running" the coach and dedicating a big alternator to the house bank is a sound strategy followed by many busnuts who stay on the move.

For those who stay stationary, all of this might not be necessary. Your regular method of keeping batteries charged via a generator, or solar, or a charger powered by the shore power, will take care of things if your infrequent movements of the coach don't really involve depleting the battery bank for more than a day or two.

Some sort of manual or automatic method of connecting the two systems together temporarily to over come a mishap of dead batteries or a failed alternator on either side is advantageous.

The cheapest way might be way of a set of jumper cables....

happy coaching!
buswarrior

[Tenor]

Thanks BW!

As they say, "the devil is in the details!"

Glenn

[Sean]

...
Otherwise, I could direct connect the 50DN to the house batteries, but that would require about 25ft of 0000 wire.  They don't exactly give that stuff away! 
...

If you plan to use the big alternator to charge the house batteries, and the batteries are really that far away, then you have no choice but to run the wire.  I guess I am a little perplexed as to how the house batteries are tied into the charging system now -- you wrote "wiring harness," but surely you would need to have at least 00 for this connection.

BTW, my house system is tied to the alternator/chassis system with 00, which is adequate for the load in my particular case, although I would probably want to go to 000 if the entire 50DN was dedicated to the house system.

-Sean
http://OurOdyssey.Blogspot.com

[rv_safetyman]

While my system is 12V, I use two alternators and keep the house and chassis system completely separate.  I do have a manual high capacity quick connect plug to tie them together in an emergency.

My reason for posting is to emphasize that you must put a fuse in the cable that connects the alternator to the house battery bank.  On mine, I put a fuse on each end of the positive cable, since each end can be the source of current if the wire should be grounded.

I also recommend you run cables for both the + and -.   I don't trust using the bus chassis for the ground.

Jim

[Tenor]

Sean,
On an MCI 7, the original start batteries were just a few feet behind the front wheels on the curb side.  Fuel tank in between.  They used 000 and 0000 wire to run power from the 50DN at the rear of the bus on the road side.  There is a master mechanical disconnect in the first by on the chassis next to the bulkhead shared by the battery bank.  In this original location is where I have my house batteries.  The Xantrex is in the front bay on the rear bulkhead connected to the battery terminals (that come through the forward bulkhead) by 0000 wire.

I added in parallel a set of gp 31's with a separate mechanical disconnect right next to the starter on the curb side of the engine compartment.  The 130A alternator is right next to the start batteries, driven by the crankshaft.

Does that clear some of the confusion?

Glenn

[Lee Bradley]

Glenn,
As I read your description, the 50DN is factory wired to charge your house bank and you added another alternator and start batteries. I assume that you have a connection between the two systems at the rear of the bus.  I would add a disconnect in that connection and connect the 130 amp alternator's regulator to the start batteries and power that regulator from the same power source as the 50DN's alternator.

[Lee Bradley]

While my system is 12V, I use two alternators and keep the house and chassis system completely separate.  I do have a manual high capacity quick connect plug to tie them together in an emergency.

My reason for posting is to emphasize that you must put a fuse in the cable that connects the alternator to the house battery bank.  On mine, I put a fuse on each end of the positive cable, since each end can be the source of current if the wire should be grounded.

I also recommend you run cables for both the + and -.   I don't trust using the bus chassis for the ground.

Jim

I understand the reasoning for the fuses but I have a hard time with that because I have had fuses fail for no apparent reason. When that happens you take out the alternator. I am still struggling with the answer to that one. I have never seen a factory fused alternator.

[bevans6]

Tenor, if your house batteries are in the stock start battery location, I would use the stock start battery wiring for them from the 50DN all the way up, including the stock disconnect switch if you want to leave it in.  I would simply completely separate the new gp32 start batteries from that wiring, wire them directly to the small alternator and the starter motor only, with a manual jumper switch to bridge the two separate systems if needed.  What this means is that all of the ancillary bus systems like running lights, defroster fans, headlights, etc, will be run from the house system and the 50DN, but I don't see any issue with that at all.  This should be totally simple to do, and would re-use just about all of the stock wiring that is already in place.

Of course, I would personally just run the 50DN to charge the starts and run the house stuff OTR anyway, since that's exactly what I did do and it's working perfectly for me so far.  In fact, if I was going to make a change, rather than adding a second alternator and battery bank for the start system I would eliminate the separate start battery bank altogether and just run both house and starts from one bank of batteries.  If I make a mistake and ran them down, I'd just charge them from the generator, which retains a separate starting system in any case.

Brian