Yet another Vanner question...

[bevans6]

We all know that the usual use of a Vanner is to equalize battery voltage when a battery pair is being charged and there is an additional load across one (usually the "bottom") battery of the pair.  This lets us run 12 volt loads from a 24 volt battery when the system is charging.

So here is my question - when drawing a +12vdc load from the pair of batteries when NOT charging, ie: boondocking, is the load draw solely from the "bottom" battery, or is the load distributed by the Vanner and drawn from the "top" battery as well?  How efficient is the load sharing, if it occurs?  If I were to have say 400 AH of batteries in total, two 200 AH 12vdc batteries, how many 12 volt amp-hours do I have access to?

"top" battery is connected to +24vdc, "bottom" battery is connected to ground.  +12vdc tap is obviously in the middle...  

Reason for the question - I am planning a hybrid 12 volt/24 volt house system, using a Vanner, and I don't know how to plan for 12 volt load capacity.

Edit - here is a follow-up, even before I get an answer to the primary question - what would happen if, with no charging source present at the 24v tap, I introduced a charging source at the 12v tap?  would the VAnner distribute that to both batteries?  Or just kind of puke?  Or ignore it?

Thanks, Brian

[Lin]

I am not an expert on this.  Vanner tech support is very helpful.  You might want to contact them before asking the unit to do anything exotic.

[BG6]

The 12+ lead pulls from both batteries at the same time -- the lower battery directly, and the upper battery through the internal circuitry.

If you are charging at 24 volts, your 12/24 setup will work just fine.  DO NOT try to charge at 12V unless you disconnect the batteries first.

That's the good news -- the bad news is that you don't want to use your coach batteries to run the house.  You need deep cycle batteries.  The best setup for these is to get 4 "golf cart" batteries in series.  The GC2 batteries you will find at most places like Costco, Sam's Club and Wally World all come from Johnson Controls, have a 225 AH rating (at the 20 hour rate) and are considered a "one year" battery (that is, 350+ discharge/charge cycles, more if you don't drain them too deeply).  At $80 each, this isn't particularly cheap, but the Trojan batteries are something like $140 each for the same specs.  The 12V deep cycle batteries don't give anywhere near the same performance or number of cycles.

With another set of batteries, you will need another Vanner (assuming that the coach had one as standard equipment).  Check fleabay, I picked up a 20 amp unit for five bucks not long ago.  The 20A is now running the coach, the 50A is on the house system.

[bevans6]

the Vanner in question is going to be on the house batteries, so that I can have both 12 volt for routine stuff like some lights, the fridge, the stove top, the fantastic fans, and 24 volt for house lights and the inverter.  The house and start batteries will be connected through a fuse and an isolation relay.  the idea is the alternator charges both while on the road, runs the inverter while travelling so I can run my rooftop AC unit, and when stopped and with no outside power or generator I can use some of the house 120 volt stuff via the inverter (with obvious limitations on amp-hours), and the house DC stuff.

If I do it this way, I will re-purpose the Vanner that is currently on the start batteries, since will have no need for that 12vdc supply, I will be able to run all 12vdc needs from the house system, since it will be charged by the alternator whenever the alternator is charging.  I kind of thought the Vanner drew power for 12vdc from both batteries but wasn't sure.  I didn't think it would distribute a charge from 12v on the lower battery to both, but another equalizer I have does do that, so I thought I would ask.

thanks for the feedback.

Brian

[edroelle]

A number of years ago, my Vanner equalizer did not work as expected.  I talked extensively to their tech., who had to investigate the situation.

The Vanner equalizes when the low battery is at a lower voltage than the upper battery.   The equalizer does not feed from the low battery to the upper.

So, if you have a 12 volt charger, you would want to put it on the upper battery bank, to utilize the capability of the Vanner.

Ed Roelle
Flint, MI

[RTS/Daytona]

to answer your ORIGINAL question

when the 24 volt charging system is not charging the batteries - the vanner will draw power from the UPPER 12 volt batteries when the LOWER 12 volt batteries are ANYTHING less than a few tenths of a volt lower than the UPPER 12 volt batteries  -- AND VISE VERSA

Pete RTS/Daytona

[BG6]

[quote author=bevans6 link=topic=16656.msg178980#msg178980 date=1279127693
If I do it this way, I will re-purpose the Vanner that is currently on the start batteries, since will have no need for that 12vdc supply, I will be able to run all 12vdc needs from the house system,
[/quote]

Bad idea.

Remember the KISS principle.  You are adding a bunch of risk factors by doing it that way, which might result in a NOGO condition for your coach, and you won't know why.

The only changes to coach electrical systems should be simplification -- and you need to know what each thing does before you change it.  The only exception is addition of a method of charging the house batteries from the alternator (300 amp isolator or isolation relay), and this should be a failsafe design which will leave the coach as it was -- the way you want to do it, the house batteries MUST be properly set up and  charged, or the coach won't run.  Imagine the aircon coming on, the inverter pulling the house batts down, and the engine computer getting spiked in the middle of your scenic trip through Death Valley.

You are way better off getting a second Vanner.  I got mine on ebay for a whole, whopping five bucks. 

[bevans6]

BG6 - Why?  Can you give me an example?

The only thing powered by the Vanner at this point is the dash radio that I installed and the two little fans on the dash.  Nothing else.  I can't imagine why you think there would be a problem, but I'm happy to be educated.  The previous owner had pulled the fuse for 12 volts, he had nothing running from the Vanner at all.   I think that when the bus was in revenue service the ticket machine ran off 12 volts.

Brian