Battery isolator and charging batteries - Help confused!

[belfert]

The more I read on battery isolators and charging house batteries from the alternator, the more confused I get!  I've done a number of searches on BNO.

My original plan was to use the 24 volt bus alternator to charge both the starting and house batteries.  I'm starting to see that this isn't a good idea because the house batteries won't charge properly as the voltage from the alternator is too low for deep cycles.  The alternator also can only monitor one set of batteries to put out the correct voltage.

Will my original plan end up destroying either the house or starting batteries?  I'll probably use a Xantrex/Heart Pathmaker to isolate the two battery banks.  Xantrex also makes a three stage regulator, but I understand that will give too much voltage to the starting batteries, plus the two banks will still charge at different rates.

One idea mentioned was a smaller single wire alternator for the bus and adding a 3 stage regulator to the 50DN 270 amp alternator for the house.  I have no idea how many amps a bus with no coach A/C really requires, but it can't be anywhere close to 270 amps.  I'd rather not deal with two alternators, but I might have to.

Help!  I have a real delimma here.  How are some of you folks handling this?

Brian Elfert

[boogiethecat]

This is an ongoing subject with many "opinions" and a few facts.  Most savvy guys like me (hee hee) just hook a solenoid-contactor between the two banks and use a little logic and intellegence on how it's turned on and off, and it works fine.  My T-105's and two group 32's have been happy as campers for the last 4 years now with this scheme... single alternator, InteliPower 3 stage converter wired permanently to the house bank... when I'm on the road the alternator keeps both banks happy, when I'm on shore the intellipower keeps em happy and when I'm in the boonies I separate em.
As far as your two banks being different voltage, well yes if one is gel and the other wet, or similar combinations of differing battery types (gel, AGM, wet) but if they are all the same whatever that is, it works fine.
  Check BNO's archives and there is a LOT of discussion on this topic. Same applies to 24 volts as applies to 12...

[belfert]

As far as your two banks being different voltage, well yes if one is gel and the other wet, or similar combinations of differing battery types (gel, AGM, wet) but if they are all the same whatever that is, it works fine.

Both of my battery banks will be wet, but I've read lots of stuff about starting and true deep cycle batteries having different charging profiles and needing different voltages to charge.

  Check BNO's archives and there is a LOT of discussion on this topic. Same applies to 24 volts as applies to 12...

I have been reading the BNO archives and that is part of the reason I'm so confused on this.

Maybe I'll just do like you did and just connect the alternator to both banks and be done with it.  I'll probably use a Xantrex/Heart Pathmaker between the two banks.

Brian Elfert

[boogiethecat]

Brian,
Yes, different charging profiles are subject to much discussion and opinion, that's for sure!!!
I couldn't find the discussion, maybe it was on the old mak site...

The cry is something like : " The two types won't match, thus one will always be undercharged and the other overcharged"

Here's somthing to ponder... say this is true and you hook the two together anyway. What will happen?

First, the bank that is the lowest in charge will take all the current the alternator wants to give it.  In the process it may drag the other bank down for a while until it comes up to
"charged" voltage, but usually not much because when charging, the voltage is usually 13 or more even across a low battery (assuming you've been a good boy and not dragged it down to totally empty).  So no harm done here.
Now when that bank gets fully charged, the other won't be harmed because it's going to be at the fully charged potential too.

As for the cry that as one bank gets fully charged the other will be overcharged... not really since terminal voltalge on wet cells is the same regardless of size.  And just for grins, say this problem could occur, what would happen? the "overcharged" battery would simply require more frequent watering...which is a good way to tell things are ok.
Even if it was a problem, checking and maintaining water levels in your batteries is something you should do before every trip anyway, and also once every few months if you're sitting.   Other than having to add water, if you maintain correct levels and don't let the batteries go dry, again, no harm done.

My Crown has 4 very old (5 years now) T105's that have been pretty well beat up but still work fine.  They like to sit at 12.5 volts most f the time even if fully charged.  My group 32's are new now (I got a free set, so why not )  I have to water the T105's about 2-3 times per year and I never had to water the old 32's.  Like I said, all these  years, no problems with the solenoid system.

I have my solenoid hooked so that I have to turn the ignition to either on or aux, and also flip a lighted switch.  It's pretty much a no brainer, although everyone has different ways of running the solenoid.  As long as however you do it makes it hard to screw up and leave the solenoid on while in the boonies, you'll be ok.

[gumpy]

I vote solenoid. That's what I did and it's been working for me for a couple years now with no problems. I charge house batteries off bus alternator when driving, and charge starting batteries off inverter when plugged in. When boondocking, turn off the solenoid which breaks the connection so I don't drain the starting batteries. My biggest issue is not having a control for it in the cockpit, but I have plans to remedy that eventually.

Ample Power has some good books on 12 volt living. There's also good information on the website of the late Jock Fuggit (http://www.purplebear.com/busnuts/bus_elec.html). Both sources are highly recommended.

craig

[gus]

I like boogie's and gumoy's sensible, no nonsense, practical approach to this subject. No long-winded, academic, the-sky-will-fall stuff that this subject usually brings on.

I do the same as these two guys except I do it manually with battery a cutoff switches on each batt. Maybe a bit inconvenient but it forces me to look at my batteries often, not really a bad thing.

[pvcces]

We use a Pathmaker and are very happy with it. Just be sure to go with a high enough amperage setup.

It appears that you can take the low amperage model and hang more continuous duty relays in parallel with the stock relay.

Good luck.

Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska

[TomC]

I too have a solenoid-actually two in parallel-160amp apiece so that if my 300 amp alternator decides to put out the full amperage, it doesn't fry the solenoids.  After 10 years of use, no problems.  I have a two way toggle controlling the solenoid. One position works off the ignition with the starting batteries and the other way is powered straight from the deep cycle batteries. In this way, if one bank of batteries goes dead the other set can power the solenoid.  Case in point, I forgot to turn on the land line after hooking up with the inverter in search mode.  I didn't come back to the bus for two weeks and the deep cycles were at 8 volts.  I turned on the shore power and discovered that the inverter wouldn't activate to charge-was just showing 'error'.  So I turned on the ignition and switch the solenoid on to get fresh 12v from the starting batteries and the charging circut in the inverter activated!  Sort of strange, but that's how it works.  As to charging to different battery banks, I have two standard wet 31's for starting and two AGM 8D's for deep cycle.  If you are charging all together, yes maybe one battery will get to full charge rate before the others, but if, say the alternator on the main engine is set at 14 volts, how can you overcharge a battery when that's the voltage it runs at all day when going down the road?  My last set of 8D's with Thermoil, I got 6 years of use, and my 31 starting batteries are over 6 years old.  So I guess I'm not frying my batteries.  Good Luck, TomC

[Len Silva]

Here's another way to accomplish the same thing with only one switch.  Using steering diodes, the solenoid will be powered from either source.

[Chuck Newman]

Brian,

I agree with most of the above, particularly the battery issue.  The main difference between a starting battery and a deep cycle battery is the thickness of the plates and some of the chemical reaction issues in the charge/discharge cycles.  But the reality is both the house batteries and engine batteries will charge fine when running on alternator.  I've never had one set of batteries last significantly longer than the other in 20 years of RVing and 42 years in electronics.

I've had solenoids. I've had solid state (diode) isolators.  I've never had either fail except in an early rental unit in the '70s.  Simply, the solenoid used by the RV manufacturer was way under-rated for the load and not a "continuous load" design.

I'm using a solenoid that is smart (off, auto, manual), has a CONTINUOUS load rating of 500 amps, and costs only $150.00 from Newark Electronics (www.newark.com).
I'm having a senior moment and can't remember the mfg name, but I can get it Monday if you're interested.

The unit is smaller than a coffee cup.  Compare that with a 300 amp diode isolator in size and price.

Chuck Newman

[DrivingMissLazy]

Brian,

I agree with most of the above, particularly the battery issue.  The main difference between a starting battery and a deep cycle battery is the thickness of the plates and some of the chemical reaction issues in the charge/discharge cycles.  But the reality is both the house batteries and engine batteries will charge fine when running on alternator.  I've never had one set of batteries last significantly longer than the other in 20 years of RVing and 42 years in electronics.

I've had solenoids. I've had solid state (diode) isolators.  I've never had either fail except in an early rental unit in the '70s.  Simply, the solenoid used by the RV manufacturer was way under-rated for the load and not a "continuous load" design.

I'm using a solenoid that is smart (off, auto, manual), has a CONTINUOUS load rating of 500 amps, and costs only $150.00 from Newark Electronics (www.newark.com).
I'm having a senior moment and can't remember the mfg name, but I can get it Monday if you're interested.

The unit is smaller than a coffee cup.  Compare that with a 300 amp diode isolator in size and price.

Chuck Newman

In some of the very early RV's, the manufacturers utilized starting solenoinds which are not designed for continous duty. There were lots of failures then as i recall. Make sure you use a solenoid rated for continous on duty.
Richard

[jjrbus]

After reading all the tech stuff from experts, it seems that you cannot have 2 battery banks in the same vehicle . So I went with the people that were doing it on a regular basis. It was suggested to me that a solenoid was complicated and prone to failure. (this by a guy with 3 slideouts on his bus!). So I went with a heavy duty selector switch, available at marine stores.  I can run bus batts only, bus and house or off.  I almost always run with both battery banks being chrarged by the bus alternator. I have no battery isolator. I'm running the AC off the inverter on the road.  I've had this setup for 4 or 5 years with no problems, no ruined batterys, no overchargeing/underchargeing, no batteries blowing up.  I always turn the switch to the off position when stopped.
                                                                                                                           Work?/Play safely Jim

[gus]

jjrbus,

Amen to that, the only difference in our two systems is that I have a cutoff switch on each battery (Four) and use the gen to run the AC. I've had absolutely no problems.

The separate switches eliminate running heavy cables (I'm lazy) and it forces me to check on the battery compartment.

I made space for more house batteries if needed but no need so far.

[jjrbus]

I do not use the generator enough to even bother having one! I can eaisely replace my 4 golf cart type batts with the L16s, same footprint just taller, but so far no need. I try to look at all the options and go with the cheap/easy way, Turns out a good inverter is the cheapest/easy way to go.

[busboy]

If your looking for a good battery isolator, you might look at a Hellroaring Technologies isolator.  I used one in the Toterhome we used to have.  When the motor was running it was charging both house and chassis batteries, when the key was off the batteries were seperated.  I added the isolator after the truck would not start at midnight in a driving rain storm in downtown Kansas City after a conference we were attending.
Happy Trails,
Brent