Split charging system

[Utahclaimjumper]

I have a split 12V electrical system on my 06, what type diode do I need to seperate my battery banks at the alternator regulator.  My shore line charging system is a 2 stage "smart" unit  (Xantrex 40Amp) that isolates the banks, but the coach system is not isolated.>>>Dan

[pvcces]

Dan, you will want one rated for at least as much current as the highest rated charging source. If you have the stock alternator, that should be 220 amps.

While you may have your reasons for going with a diode type isolator/combiner, I would get one of the high current audio relays that are available many places online and find a way to turn it on when there is charging power available.

If you get an isolator that uses silicon diodes, there will be around 1/2 volt drop across it. At maximum charge, there will be over 100 watts of heat generated in the heat sink that is unlikely to do you any good.

If you want to use a diode design anyway, then be sure to use an isolator that uses Schottky diodes. They will only have a drop of around 1/3 that of silicon diodes, so will only waste about 2/3 of the energy.

Usually, the house bank is deep cycle and requires a higher voltage than the start bank for recharging for any given charge rate. Since the house bank usually will need a much larger recharge than the start bank, that will aggravate the recharge drop problems. A relay will get you almost no drop if properly sized and minimize the recharge problems.

If you use the master switch, you can trigger the relay by placing it in the run position. Or, you might use the voltage regulator input to turn it on. We use the Pathmaker by Xantrex; it will turn on if either bank is being charged and disconnect anytime neither is charging.

It also disconnects if system voltage goes too high. If you use the remote, it can give you 5 minutes of interconnect for emergency starting, if you should need both banks for starting. It will also let you manually disconnect the banks. We like ours.

For what it's worth.

Tom Caffrey

[kwidd]

Here's what I've been using on the trucks at work. I've been satisfied with there performance. They are a little pricey but worth it. Kent   http://www.perfectswitch.com/

[Sojourner]

Here's what I've been using on the trucks at work. I've been satisfied with there performance. They are a little pricey but worth it. Kent   http://www.perfectswitch.com/

Thank you for the link.

[Utahclaimjumper]

Kwidd, thanks for the link, great info.  Tom, thanks for the info, I was thinking along the lines of a relay on the coach bank leg, activated by the master, to close that path when the engine is dead, thus preventing any feedback between banks.  I already have a good working system for combo starting if needed.  Thanks again>>>Dan

[Len Silva]

Dan,

You might consider operating the relay through a fuel pressure switch or other method that indicates the engine is actually running and not just that the master switch is on.  Even better is a setup that knows the alternator is actually charging before switching.  Perhaps from an Air Conditioning relay depending on your particular bus.

[Utahclaimjumper]

Len, thats what got me thinking about diodes so it would be a one way path that that would require no attention, I didnt think about all the other problems with diodes. Probably the best for the least would be a relay.>>>Dan

[JohnEd]

Dan,

Tom seems to have the hot setup and most comprehensive advice.  I have 30 years in electronics but that only means I am confident that I understand what he is talking about.  His Xantrex approach is spot on no doubt but probably spendy.  Then again, so are batteries.

My coach was set up with STARTER SOLINOIDS, "continuous duty" type, to strap the batteries together for simultaneous emergency starting power from the alternator.  You can configure those starter solenoids in all sorts of ways to do many things.

I use those cheap(er) high current battery isolators.  Possibly those made by Cole Hersey.  Shop around for those as the prices vary a lot.  Tom is right about wanting as little voltage drop as possible across the diodes.  You can relieve that concern and get a much better charging system in the process as follows:  Your regulator is either internal to the alternator or external.  The external alternators have a connection labeled "battery".  The level of voltage put out by the alternator is tied to the voltage on that terminal.  Now if you run a wire from that regulator terminal to the battery terminal, and I did not say "any B+ point", the regulator will set the alternator to the correct charge voltage at the battery and isn't that where you want it regulated to?  As your system ages and the quality of the connections deteriorates, your charge voltage will self adjust to always keep the bats at full charge.  You can incorporate all the sophisticated devices you want, and many are beneficial, but the charge voltage is the critical element.  That is till you solve that and the next becomes the "critical element".   If your alternator has an internal regulator, fear not, your local alternator rebuild shop can show you how to "break out" that wire so you can pick up the battery charge voltage.  Have you ever looked up the relative charge condition of a battery charged to 12.6 volts versus 12.1???  Do that!

The double ought cable that goes to my generator starter is connected to a solenoid that is controlled by the start signal that goes to the generator solenoid mounted on the generator.  Seems redundant and way back when I eliminated the first solenoid when it failed.  Bad mistake that looked good on the schematic I drew.  The first solenoid protects everything down stream from the battery connection, including that big heavy cable that most assuredly would burn all the wiring in that cable way or burn down the coach.  All that glitters is not gold and all that.

HTH

John

[Utahclaimjumper]

Tom, I researched the Xantrex pathmaker 250 Amp 2 bank, best price found  $305.00. A bit pricey to say the least, but engineered to do the job. Looks like the best "set & forget" deal, but cant get over the heartburn of that cost, sure wish I lived in AK where all the momey is.>>>Dan

[pvcces]

Dan, check out this auction: 130287157617. I think that it might relieve your heartburn a little. Also, check on this auction: 270341403951. Here is one for a remote, but I have bought those for around 25 to 30 dollars: 220330971329.

When we were setting up our Pathmaker, I bought one of the single relay 100 amp models. It had a cheap White-Rogers 80 amp relay on it. So, I bought one of the high current relays and replaced the original with that. It's been trouble-free.

If you have experience buying off of eBay, you should be able to scare up some of these deals. Also, if you would like to go that route, I belive that Pete Pampas was selling or showing where you could get good 200 amp relays for around $55.

Good luck, whichever choice you make.

Tom Caffrey