What is best way to hook alternator to house batteries?

[TomC]

To prevent from cranking with the deep cycle batteries (I have 2-8D AGM), this is why I installed the dash switch to select being activated by either the cranking batteries through the ignition switch or the deep cycles.  Normally I have it off, and only turn it on when driving for a length of time.  It is nice to have manual control.  Good luck, TomC

[bobofthenorth]

I hope you mispoke here.  What it actually means is that the house bank is assisting to start but the house bank is only peripherally involved in our case.  There is a lot of resistance between the house batteries in the spare tire compartment and the starter c/w the path from the start solenoid to the coach batteries.  I'm sure there's some amps flowing through that crossover cable when we start but to say that all the chassis batteries do is energize the solenoid is silly.

I don't know for sure in your case, but I would ask if you've measured it?  A lot depends on the relative size of the banks.
<snip>
So I think you might be surprised if you actually measured how much current comes out of your house bank during cranking.

Well you are right - I am surprised - but maybe not as surprised as you thought I would be.  I got my swamper back yesterday and today we measured the load on the house bank while cranking the noisemaker.  It starts so quickly that it is hard to get a good reading but it is somehwere between 50 & 60 amps which is more than I expected but nowhere near enough to start an 8-92.

So I owe Sean an apology.  He said all my start load was falling on my house bank & I said that was silly.  I'd say neither one of us was 100% right.  Mea culpa maximus.

[Sean]

...  It starts so quickly that it is hard to get a good reading but it is somehwere between 50 & 60 amps which is more than I expected but nowhere near enough to start an 8-92.

I was hoping you'd post the results, because I've been wondering how much difference your 8D's would make over my tiny car batteries.  A good bit, it would appear.

I would guess you're not getting an accurate reading if your meter is digital and the thing fires quickly.  You might turn the fuel off at the rear switch and try cranking again to get a better figure.  I would guess you're somewhere north of the figure you posted.  Still, that's a long way from the ~120 or so that I am seeing.

This is why I wrote that a lot depends on the relative size of the banks.  My giant house bank, with eight size 8D, completely overshadows the two puny group-65 chassis batteries.  They have enough oomph to start the big Detroit, even in the cold, but if they are not isolated, that enormous source, even 20' away over 00 wire, is just too easy to access.

-Sean
http://OurOdyssey.BlogSpot.com

[Tony LEE]

I use one of these

http://www.redarc.com.au/pdfs/Flyers/SmartStartR.pdf

Only charges house battery once start battery is charged after starting. Can be switched to provide emergency boost or switched off if you don't want the house batteries charging all the time.

My alternator puts in about 160 amps for the first half hour and then it tapers off over the next couple of hours. I usually switch it off then and let the solar finish topping it up under more controlled conditions.