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Author Topic: Mixed battery types on same charger?  (Read 862 times)
richard5933
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« on: November 03, 2017, 07:37:12 PM »

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?
« Last Edit: November 04, 2017, 03:36:31 AM by richard5933 » Logged

Richard
1974 GMC P8M4108a-125 (Current Bus)
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« Reply #1 on: November 04, 2017, 05:15:10 AM »

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
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« Reply #2 on: November 04, 2017, 07:43:54 AM »

  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
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Bruce H; Wallace (near Wilmington) NC
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« Reply #3 on: November 04, 2017, 08:23:31 AM »

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...  Smiley
« Last Edit: November 04, 2017, 08:27:16 AM by bevans6 » Logged

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« Reply #4 on: November 04, 2017, 08:26:28 AM »

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.
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« Reply #5 on: November 04, 2017, 09:58:26 AM »

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
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« Reply #6 on: November 04, 2017, 10:10:09 AM »

  ...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.
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Bruce H; Wallace (near Wilmington) NC
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« Reply #7 on: November 04, 2017, 10:51:45 AM »

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.
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« Reply #8 on: November 04, 2017, 11:13:22 AM »

   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.)
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Bruce H; Wallace (near Wilmington) NC
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« Reply #9 on: November 04, 2017, 12:06:12 PM »

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.
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« Reply #10 on: November 04, 2017, 03:06:56 PM »

Yeah, depending on how remote you may be,extra backup options make sense.
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« Reply #11 on: November 04, 2017, 06:03:29 PM »

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
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« Reply #12 on: November 04, 2017, 08:53:11 PM »

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 ?
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« Reply #13 on: November 05, 2017, 03:43:47 AM »

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.
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Richard
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« Reply #14 on: November 05, 2017, 07:28:32 AM »

are you saying your generator has no alternator ?
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« Reply #15 on: November 05, 2017, 07:55:42 AM »

are you saying your generator has no alternator ?
Correct. There is a charging circuit in the generator, but it is single stage and will keep charging after the battery no longer needs. Seems to be a battery boiler. No alternator and no way way to add one.

Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
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« Reply #16 on: November 05, 2017, 08:06:51 AM »

At least with my Powertech 10kw with 4 cylinder Kubota, it too has an electric fuel pump and fuel solenoid. The gen is attached to the 2-31 starting batteries. I've dry camped 4 days and still the big engine started just fine (no charging on the generator-12v alternator is disconnected). Good Luck, TomC
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« Reply #17 on: November 05, 2017, 08:21:30 AM »

Any of these non-alternator "charging circuits" I've seen have poor voltage levels for charging, often below 13 volts.

Put a meter onto that charge source before you dismiss it, you may already have a solution for underway, and then a simple trickle charger is all the gen battery needs for between times?

That relatively well charged 8D, if inter-connected, can contribute to fooling your charging devices into lowering the charge sooner,  on the rest of the depleted bank, extending charge times.

As usual, there are the different scenarios. Everything is in storage, all the batteries are sufficiently charged, it doesn't really matter what you do... out camping, pulled the house bank down overnight, a quiet venue, a short 100 mile re-locate...

Lots of busnuts unwittingly have sufficient hardware for happy daily 100% charging, but connect stuff up and deploy it in ways that makes far less.

Adding more fancy hardware does not necessarily fix the problem? But it sure is fun messing around with, both in thought process and application!

Don't tell the Admiral what it all costs...

happy coaching!
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« Reply #18 on: November 05, 2017, 08:23:15 AM »

I think there may be more use from the 8D than just starting, not sure what yet.  Though im interested really lately to why you, TomC needed to disconnnect the genie alternator. If you could please explain a bit more if ya can.  

Good day
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« Reply #19 on: November 05, 2017, 09:16:03 AM »

I think there may be more use from the 8D than just starting, not sure what yet.  Though im interested really lately to why you, TomC needed to disconnnect the genie alternator. If you could please explain a bit more if ya can.  

Good day
Floyd
My guess would be that since he is connected to the chassis batts for generator starting, that while running down the road with both the big engine alternator going and the genny alternator going he was having a battle going on between the two resulting in less than optimal charging performance. My genny is connected to my house bank and i too had to disconnect the alternator on the genny becuase my inverter smart charger and the alternator were not playing nicely together.

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« Reply #20 on: November 05, 2017, 12:20:27 PM »

I use this type of charger maintainer to keep my house back up geni charged and had 2 separate units on each of the start batteries ( mci 24 volt system ) all on a switch for each unit  so I could control when I wanted them on or off . this way you do not boil the batteries .

 http://www.canadiantire.ca/en/pdp/motomaster-eliminator-intelligent-battery-charger-2a-0111506p.html#srp 

dave
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« Reply #21 on: November 05, 2017, 02:43:11 PM »

Charging circuit on the generator brings the battery voltage up to about 12.8 which is not enough to charge properly. It also doesn't automatically shut off and will eventually boil the battery.

My plan at this point is to use the Echo Charger to keep the generator start battery topped off. If I find that the generator fuel pump and fuel solenoid draw more than 15 amps, I'll move their feed so that they run off the house batteries (which are being charged by the PD 9270). That would leave the 8D strictly to start the generator, and it would be isolated from the house system - if one of us accidentally runs down the house batteries we can still start the generator. I guess it will be nice to have the 'extra' 8D in case one of the chassis batteries craps out on us while on the road.

Maybe one day I'll get a new Wrico generator and all this will be moot. Till then I will work with what I have.

Got to say though, overall this coach is in great shape and I'm thrilled that I'm only having to refresh and update a few of the house/RV systems. The techs at the shop didn't really believe me when I made the appointment for maintenance and inspections as I told them what I was bringing in. Once they got their hands on it they said it was in better shape than many of the charter coaches they maintain for the local company, even their newer ones.

Now I just have to figure out how to be patient until spring arrives...

« Last Edit: November 05, 2017, 04:58:34 PM by richard5933 » Logged

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« Reply #22 on: November 05, 2017, 04:56:06 PM »

There is nothing wrong with using that existing charge source at 12.8. You'll never "boil" a battery with that.

Remember, the generator battery is in a perpetually fully charged condition, starting the generator is meaningless to an 8D battery, it needs hardly a handful of electrons to replace what starting the generator took out.

A lead acid battery at rest, fully charged, surface voltage gone, is commonly said to be 12.6 volts.

The fuel pump and solenoid will run just fine off the existing charging circuit, that's why it's there!
Moving them to the house battery, and then killing the house bank... you get no generator either.

The principle of redundant/isolated systems, is to keep them isolated.

The charge circuit shuts off when the generator does, and won't do any harm to your generator battery.

Just like a garden tractor, outboard motor, and countless other applications with a magneto style "charger", an occasional treatment with a battery tender will put any fears to rest about being a battery murderer, if you can even get one to engage the charge when connected.

The fewer pieces of equipment, the fewer failure points, the fewer things to inspect, the fewer things to remember?

happy coaching!
buswarrior

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