Dual battery control switch

[kerry]

The hard-wired-in-parallel dual battery system in my FG seems to provide few advantages and lots of the disadvantages of a two battery system. The sole advantage that I can see is lots of reserve capacity in cold weather. The disadvantages are that you always have to buy two batteries when replacing and a failed single battery will eventually destroy the remaining good battery with no indication that the destruction is taking place.
On an expedition camper especially it seems that dual batteries should be wired to make optimum use of having two batteries, namely having one battery in reserve if a single battery fails, the way that many boats are set up, the option of using both batteries at once and the capability of being disconnected while in storage.
Consequently, I am planning to install a dual battery control switch on my truck which allows me to choose one or the other or both batteries to be hooked to the truck system and also allows both batteries to be disconnected. Perko makes a heavy duty switch rated for 850amps. (http://gator49.hostgator.com/~zeromyst/ecatalog/product_info.php?cPath=141_142_145&products_id=149) I'm guessing this switch is made for big boats with big diesel engines. It's the highest amperage switch I've been able to find so far in my google searches. What are people's opinions on this amperage rating for the FG? I currently am running a battery rated for 850 max CCA's and it seems to be starting fine.

 

[Antichrist]

That switch is only rated at 350 amps continuous. At 850 amps it's intermittent, 5 minutes on, 5 off. That might be ok for your application, but just need to keep it in mind.

 

[kerry]

I was thinking about the starter mainly since there's nothing else on the truck that would draw any high amperage. I haven't put an ammeter on the starter so I don't know for sure what it draws but I doubt it draws anywhere near 850 amps.

 

[Antichrist]

Yeah, for the starter type loads that would be fine. I'd be surprised if the starter even draws 350A, and even if it did draw more, I seriously doubt you'd be cranking it long enough to exceed the duty cycle of the switch.

 

[dzzz]

For more money Blue Sea makes some nice switches that can be operated remotely.

Another reason to add a switch is that solar panels won't charge with the truck running when batteries are combined (the alternator is in the solar charger circuit).

 

[whatcharterboat]

Yeah, for the starter type loads that would be fine. I'd be surprised if the starter even draws 350A, and even if it did draw more, I seriously doubt you'd be cranking it long enough to exceed the duty cycle of the switch.

Even if it did, the switch wouldn't see it, would it? It is only going to see the potential difference of the current between the 2 batteries. It shouldn't need to handle the entire starter load but closer to half of it . Well depending on how discharged one of the batteries is anyway.

This is a good idea Kerry. I've always thought that the battery bank on these trucks was an overkill but they can still give grief occasionally. Being able to manage the batteries as a bank rather than as one battery has a lot of merit. A VSR is probably a good way to do this too.

 

[kerry]

For more money Blue Sea makes some nice switches that can be operated remotely.

Another reason to add a switch is that solar panels won't charge with the truck running when batteries are combined (the alternator is in the solar charger circuit).

I did come across some Blue Sea switches in my searching but none as heavy duty as I recall. Remote is nice, but I do like the feel of grabbing that knob and turning it manually. There's little doubt involved.

 

[kerry]

Kerry - Bluesea has a number of high amp bat switches - http://bluesea.com/category/1

You might want to integrate your house & two starting batteries into a three battery integrated system - in my build I just treated my double starting batteries as one (with all the drawbacks you mentioned) your post got me to thinking I'd have been better off treating them as three - using one of these three switch panels. Battery isolation/emergency combining is really easy to set up with these-Peter
http://bluesea.com/category/1/productline/5

Yes, if I was starting from scratch, that would have been the best system. I've already installed a relay isolating the camper battery from the starting batteries so at this point it seems easiest to separate the two starting batteries with a switch. I just ordered this Blue Sea one http://bluesea.com/category/1/products/9001e since it was rated at 2000amp starting draw.

 

[1Engine]

Yes, if I was starting from scratch, that would have been the best system. I've already installed a relay isolating the camper battery from the starting batteries so at this point it seems easiest to separate the two starting batteries with a switch. I just ordered this Blue Sea one http://bluesea.com/category/1/products/9001e since it was rated at 2000amp starting draw.

That should be plenty of capacity, the engines that I have at work are MTU 16V2000 rated at 1500hp & are 32liter capacity & they only dray 650amps @24VDC while cranking.
I prefer the voltage sensitive relays, over here in Aus Redac make a good reliable unit http://redarc.com.au/static/files/SBI-flyer.pdf & they have some good ideas of different hookup arrangements http://redarc.com.au/knowledge-base/wiring-guides