Multiple 24V alternators. Do or Don't?

[rv_safetyman]

Lee, I understand your point, but a 24V 200+ amp alternator is basically the same as a welder of the same amperage and if the cable shorts out, you WILL have a ton of damage and most likely a fire.  The problem is you can shut down the engine, but he cable is still hot from the battery bank.

In my case, I would be loosing a fairly inexpensive truck alternator.  That would probably not happen since it is a one wire unit.

I just get paranoid thinking about the possibility of a big fire.

Not a challenge, but just trying to be better informed:  if you would loose the 12/24V supply on a 50 DN is it a given (probability?) that you will damage it?  If it is damaged, what is the likely failure mode (asking to think about what the repair cost might be)?

Jim

[Lee Bradley]

Automotive alternator are wound to be current limited via back EMF so long as the batteries are connected. Without that load the back currents in the stator take out the diodes and the stator its self if you're unlucky.

I think I am going to go the route of most of the electric hand tools and double insulate the system; 0000 welder cable inside flexible plastic conduit inside the bus utility run for about 12 feet. 

[Tenor]

OK Lee, you are following the train of thought I have.  Wire gp 31's direct to 130A alternator and starter.  Disconnect feed to bus chassis by switch.  No problem.  My gp 31's are already directly connected to the 130A alternator and there is a master disconnect between the gp31's and the starter.  Just move the disconnect from there to between the starter and the bus chassis.  There should be no drain on the gp 31's since they only feed the starter.

Use the factory wiring harness for the 50DN.  Connect the house bank to the chassis before starting so that the house batteries send the 24V signal feed to engage the starter relay.  50DN supplies the current for the house and the bus chassis needs.  Do I have it right?

I sure do appreciate all the help!

Glenn

[Lee Bradley]

Sounds like a plan.  I'm not sure that you would have to connect the house and start batteries before starting. The house batteries should power the starter relay through the standard bus safety interlocks and connect the starter motor to the start batteries.

[Tenor]

Well, these changes are made as well. The 130A alt charges the start batts only and they will constantly be connected to only the starter and the alternator.  There is a master disconnect between the starter and the rest of the bus systems. I can flip the switch for emergency starts or just to top off the start batts while parked.

The 50DN is factory wired to the bus chassis, and will supply power to the house batts and bus systems while driving. The original master disconnect allows me to separate the house batts from the bus while parked.

Last question- what voltage should I set the 50DN at?

Thanks!

Glenn

[thomasinnv]

Well, these changes are made as well. The 130A alt charges the start batts only and they will constantly be connected to only the starter and the alternator.  There is a master disconnect between the starter and the rest of the bus systems. I can flip the switch for emergency starts or just to top off the start batts while parked.

The 50DN is factory wired to the bus chassis, and will supply power to the house batts and bus systems while driving. The original master disconnect allows me to separate the house batts from the bus while parked.

Last question- what voltage should I set the 50DN at?

Thanks!

Glenn

the book says under ordinary conditions and up to 70 degrees, the proper voltage setting is 27.6.  Over 70 degree is 27.5 volts. The book also says this is just a guideline and final adjustments should be made on the basis of battery charge level and water usage. My voltage ended up being slightly higher than that in order to maintain a full charge (somewhere around 28 if i remember right), but with no water usage. YMMV.

[bevans6]

Phone the people who manufacture your batteries and ask them what voltage to set at.  I did, I have US 2000 6 volt deep cycle batteries, and the tech support person told me to charge them at 28.5 - 29 volts, which I thought was quite high.  He said that was what they needed to get a full charge, and that at 27.5 (where my alternator is currently set) they would never achieve a full charge.   He said they had different needs than the start batteries.

Brian

[Tenor]

Brian,
Trojans website has the same rating.  I'll crank it up a bit. 

Glenn