Mixed battery types on same charger?

[richard5933]

Trying to make final decisions on how to set up the house system on the 4108. For right now, I'm going with a 12v house system. The house batteries will be charged with a Progressive Dynamics 9720 charger which puts out 70 amps while on shore power or generator.

The generator also has a start battery. Right now it's an 8D. I know it's overkill for a generator, but it's brand new and sits in a nice tray with room to spare.

Question is how to best keep the generator start battery charged. Couple of options I see. I'm sure there are also some I'm missing.

1) One method would be to use an automatic solenoid to bridge the generator start battery to the house batteries whenever the generator is powering the Prgressive Dynamics 9720. My question here is if it's okay to run the 8D parallel to the house batteries which will be four Trojan L16 set up in series/parallel to run 12v. I wasn't sure if it is okay to connect the 8D and the Trojans together like that while charging. My gut feeling is that it's no different than when I used to bridge the house batteries to the chassis batteries on the 4106 to charge over-the-road. All the batteries are flooded cell.

2) I can use an Echo Charger to pull 15 amps from the house battery charger to charge the gen start battery. My concern here is if 15 amps will be enough. The only thing that the gen start battery powers right now is starting the generator, running the Bendix fuel pump for the gen, and holding the fuel solenoid open on the gen. The last two items could be re-routed to run off the house batteries if needed, which would leave the gen start battery doing nothing but starting the gen. Assuming that the 15 amps is enough to keep up with the fuel pump and fuel solenoid, this would be my preferred option.

3) Eliminate the gen start battery and just use the house batteries to start the generator. However, my main reason for wanting to keep the separate start battery for the gen is to eliminate any chance of running down the house batteries down too low overnight by accident and then not being able to start the generator in the morning.

4) Install alternator on generator. This was going to be my method to keep the gen start bat charged, but in the space where the alternator & bracket is supposed to go is a bunch of other stuff. Some could be moved easily. The rest looks at first glance like it would involve some fabrication to the brackets and plumbing system being used for the generator's cooling system.

I know that there are more complicated and automated systems out there for things like this. For right now, I'm looking for a pretty simple and fail-safe method that uses a minimum of equipment and rewiring.

Thoughts? Is there something easier I'm missing?

[TomC]

I have a very simple system. 2-31 batteries for starting the bus and to run the generator. 2-8D Lifeline AGM deep cycle for house batteries. I have a 2,500 watt Trace inverter/charger wired to the house batteries. The deep cycle batteries can be charged through the inverter when on power pole or generator is running or with a jumper relay that connects the starting and house batteries. I disconnected the small belt driven alternator on the generator because it was interfering with the big 300amp alternator on the engine-it is just used as a belt tightening. As to the generator being wired from the starting batteries-I have sat for 4 days running the generator twice everyday with no problems. When I want to charge up the starting batteries, I turn on the jumper relay to connect the starting and house batteries, then the inverter tops off the starting batteries. The generator just doesn't take much battery power when running. Good Luck, TomC

[Oonrahnjay]

  I have a very simple system. 2-31 batteries for starting the bus and to run the generator. 2-8D Lifeline AGM deep cycle for house batteries. I have a 2,500 watt Trace inverter/charger wired to the house batteries. The deep cycle batteries can be charged through the inverter when on power pole or generator is running or with a jumper relay that connects the starting and house batteries. I disconnected the small belt driven alternator on the generator because it was interfering with the big 300amp alternator on the engine-it is just used as a belt tightening. As to the generator being wired from the starting batteries-I have sat for 4 days running the generator twice everyday with no problems. When I want to charge up the starting batteries, I turn on the jumper relay to connect the starting and house batteries, then the inverter tops off the starting batteries. The generator just doesn't take much battery power when running. Good Luck, TomC 

      Thanks, Tom.  One question though, does the generator have to have an outside power source for making power or is it "self-energizing" when it's running.  I guess I'm asking if it has to have something like the field terminal on an engine driven alternator?  (I'd certainly think it would not have to have an external source, but the question came into my head -- it would sure work better if it were self-supporting once it's started).
      Second question, if someone has a separate generator battery and every battery on the bus has been run low on power, can ordinary jumper cables from the toad battery be used to start the generator?

Thanks for the info,  BH

[bevans6]

The PD 9270 ( spelling it right helps on the google search) is a converter, not a charger - although it does both, it is biased towards supplying a constant 13.6 volts to power house loads.  It also has a smart charger mode that it can go into if it detects a low battery in need of charging.  At that point it goes into a "boost" mode, where it might deliver up to it's rated 70 amps for a very short period of time to start the battery charge process, at which point it goes back to it's "normal" mode of a plain 13.6 volts.  Charging at 13.6 volts isn't bad for a battery, but it's not as good as a typical 14 or so volt absorption charge and then dropping to 13.2 - 13.6 volts for maintenance.  The PD9270 will detect a storage situation and drop to 13.2 volts for long term storage.  If you turn on a light, or leave the fridge on so there is a load, it detects that and goes back to 13.6 volts.  For RV (and bus) use, almost a perfect scenario for the required combination of supplying power to a house (which honestly is what most RV's do 90% of the time) and charging and maintaining batteries.  It also has an equalize mode that is very good for batteries, but can be bad for things plugged into the 12 volt feed in the house (it's 14.4 volts, which might be a little high for some devices, but probably not).

It is designed for lead acid batteries, and while it mentions that, it doesn't mention SLA/AGM batteries, which require a different charge profile.  So I would stick to wet cell lead acid batteries.  Typically the maximum safe charge rate for lead acid batteries is 15%- 20% of the 20 hour amp-hour rating, so with a 70 amp charger I would pair that with no less than 350 AH of battery bank.  This means that if you connect it to charge a small battery you stand the chance of really overcharging it if it goes into "boost" mode.  Four L16's would give 740 AH at 12 volts, so a 70 amp charger is completely appropriate.  If I have a choice I always set the charger for 10% of the battery bank size, good compromise between speed and battery life.  AGM's again are completely different in this respect.

Charging different batteries from the same charger.  I do it all the time, I normally leave my inverter connected to both the house and start batteries for over-winter storage, for example.  The batteries won't charge evenly, and the smart programs in the PD9270 will monitor and react to the mix of battery state of charge, leading to sub-optimal charging in some circumstances.  But it's kind of a moot point if the batteries are somewhat matched, like a typical new 8D paired with a setup of L16's in series/parallel.  Your idea of the second smart DC-DC charger would optimize the charging of both systems, if I understand how it works correctly.

A generator's 120V/240V AC alternator is self-energizing, it doesn't need external power to start generating, as a pretty standard rule of thumb.  If it does, the start battery would be it.  It's 12v alternator (most have one to charge the start battery) would probably need to have a battery connected to it to run properly.  Any 12v battery can jump start the generator (if it's battery is a 12v battery), so the toad battery would be fine.

I think that's all I got...  

[RichardEntrekin]

The short answer to can the gennie be jump started by the car is yes.

Two things to keep in mind are that it must be accessible and within reach of the jumper cables which is kind of obvious. For example my gennie is on air operated enclosure. No air, no access. Sometimes no power results in no air.

But more importantly to remember is that if the battery bank that is powering the gennie is too low to start the gennie, then that bank MUST be disconnected before you try to jump. There is no way that the alternator from the car is going to overpower a bank of discharged 8D's. Been there done that.

[richard5933]

Guess my question was more about how to keep the 8D which serves as the generator start battery charged.

The generator does not have an alternator to charge the 8D. There is a charging circuit in the generator for keeping its battery charged, but it is an on/off setup and will just keep charging eventually boiling the battery.

My goal is to keep the 8D charged. The two ways I see that would be easiest are 1) use an Echo Charger to send 15 amps from the house battery charge to the generator start battery, and 2) bridge the generator start battery with the house batteries when the generator is running

Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
KD9GRB

[Oonrahnjay]

  ...A   generator's 120V/240V AC alternator is self-energizing, it doesn't need external power to start generating, as a pretty standard rule of thumb.  If it does, the start battery would be it.  It's 12v alternator (most have one to charge the start battery) would probably need to have a battery connected to it to run properly.  Any 12v battery can jump start the generator (if it's battery is a 12v battery), so the toad battery would be fine.  ...  

      Thanks for this info, Brian.  It's what I thought about issue of external exciting power (it would be pretty useless to have a generator that required external power when the issue is that you don't external power and that's why you need the generator -- but I wanted to be sure that that was the case.
      Thanks for the info on the jump starts, too.

 The short answer to can the gennie be jump started by the car is yes.

Two things to keep in mind are that it must be accessible and within reach of the jumper cables which is kind of obvious.  ...  

      Good to know that.  I'm pretty sure that the jumper cables that I carry in my car are 9' and may even be 12'.  My generator is in a compartment that's accessible to the outside (lockable latches) and the battery is easy to reach -- in fact, the edge of the battery is just an inch or two from the inside surface of compartment door and it's about 5' 6" above ground level.  I can't see that it's going to be any problem to get a toad close enough to jump.

 But more importantly to remember is that if the battery bank that is powering the gennie is too low to start the gennie, then that bank MUST be disconnected before you try to jump. There is no way that the alternator from the car is going to overpower a bank of discharged 8D's. Been there done that.  

      Good info but I have a separate automotive starter battery (Type 27 or 29, I think) mounted within inches of the generator enclosure itself.  Unless I have another severe problem, I should be able to start my generator no matter what the state of the house or starter banks, either on the battery itself or by a jump from the toad.  I like redundancy.

[chessie4905]

How about getting one of those almost pocket sized li-on jumper units. One of the better ones for times you can't get generator started? They make these to start diesel trucks also by having larger capacity.

[Oonrahnjay]

   How about getting one of those almost pocket sized li-on jumper units. One of the better ones for times you can't get generator started? They make these to start diesel trucks also by having larger capacity.   

       Oh, I forgot -- I did!   (I actually bought it for my TDI 1.9 liter since it's nearing 450,000 miles -- no problems, but I'm keeping my eye on preventative maintenance and backup capability.  It's rated for diesel pickups up to 6.8 liter engine size, so it should be good for the generator, too.)

[windtrader]

Those portable power source/starter units work fine for jumping the generator battery as it typical auto size. However you wire it all up, just make sure you have some failsafe way to get going(starting) if you are along and off the grid.

[chessie4905]

Yeah, depending on how remote you may be,extra backup options make sense.

[TomC]

You want the simplest way to keep the 8D gen starting battery charged? Just go to auto supply and get one of the better battery chargers that is automatic. Then just keep attached to the battery and when you start the gen, the 120vac will charge through the battery charger. Good Luck, TomC

[eagle19952]

uhm...what will drain this 8d battery ?   that battery if worth a toot should hold a charge for 6 months or more....u will start the gen atleast twice a year, won't you ?

[richard5933]

uhm...what will drain this 8d battery ?   that battery if worth a toot should hold a charge for 6 months or more....u will start the gen atleast twice a year, won't you ?

When the generator runs it requires 12v to power the fuel pump and the fuel solenoid. And of course starting. Even if we use the generator for a few hours a day while camping to charge batteries, make hot water, etc. we will need to keep it charged. After thinking about this for a few days, hooking up an Echo Charger to suck 15 amps from the house batteries to charge when needed seems like the easiest solution, but that would only work if the load imposed by the generator is less than that. I'll have to do some research on the loads and see if I can determine how much current they require.

[eagle19952]

are you saying your generator has no alternator ?