i am planning on doing a dual battery conversion on my 84 f-150 with the 300 inline. i have a marine application switch that has four positions, battery 1, battery 2, both batteries, and off. i was wondering if anyone on here has any experience wiring something like this up or happens to have a diagram around. any help is appreciated since i got the switch used and don't have any instructions with it. thank you

 

Try the electrical forum.

 

This type of manual switch could be wired as a simple on/off for your 2nd battery, but you'd have to remember and set it to the right position each and every time else the #2 battery wont charge, or you'll drain you main. These switches are not isolators, but battery selectors to let you crank your engine [think big inboard diesel] with either battery or both together for maximum amperage. They're usually wired in conjunction with an isolator. Wired without an isolator there's a direct connection between the two batteries, so if one is heavily drained the charged battery will rush it with current as soon as they're connected, draining the charged battery and possibly damaging the discharged one.


What you really need a solid state dual battery isolator. It will let your 2nd battery charge but automatically prevent any load connected to it from draining your main battery. Isolators are basically a couple of BIG high current diodes made into a heatsink. They function as electrical 1-way check valves, letting power from the alternator charge both batteries, but keeping them from "feeding" off each other when the alt. isn't charging. A 95 amp isolator will usually run $45-$65, last one I bought came from Advance auto parts [aka Checker, Kragen, Murray's] and was only $35. Same brand [Sure Power] other stores had at $50 or more.

Avoid the relay based "isolators", which aren't isolators at all, just an automatic switch that connects both batteries while the vehicle is running. They're not reliable long term and drain 5-10 amps of power. They also have the same problem as a manual switch where a charged battery will rush a dead one with too much current causing damage.

 

Is the battery switch a big black switch by K-H? if so, find the local Ambulance service and ask who Does the electrical work for them and they can help with the diagram. Ane you do need a battery isolator as 83van said. Other wise if you shut off the batteries with the engine on you run the risk of alt/voltage regulator and othe electrical damage. We had that happen alot in the old days before isolators were required.

 

no its not by k-h, its out of a boat. so i am guessing the switch is the cheap part of the conversion. i already have the battery and the switch. how many of those isolators would i need?

 

I wouldn't put in a switch unless you are using the second battery as a deep cycle battery. I'd grab parts off a diesel and bolt them right on - including the alternator.

 

the reason i want a switch is so i can run accesories with the truck turned off and then switch back to the good battery to start the truck or if i go on vacation for a week or something i can turn off both batteries. i definatly want the switch, i want all my stuff to work no matter which battery i have selected.

 

If you are going to dischare the batteries regularly you need a deep cycle battery or it will get damaged. Regualr batteries can't handle that stuff. To do that you will need to charge at a higher rate than normal. You'd need a second alternator and voltage regulator. That would also allow you independent systems, and you could put a solenoid between in case the one goes dead.

 

You only need one isolator for a standard two battery setup. This boating site has a good basic diagram for the type of hookup you'd be looking at if you want to install the switch:

http://www.boatfix.com/how/Battery4.jpg

Advantage to the switch is that it would let you start the engine with #2 battery [or both] if needed, at the expense of a long run of heavy gauge cable assuming battery #2 is on the drivers side. From that distance use 4ga cable if you want to start with it.

Disadvantage to the switch is that when set to "both" you've bypassed the isolator. If one battery is significantly discharged the "good" one will backfeed into it. Adding the switch also requires about double the # of electrical connections... and we all know how much of a problem rusted/ corroded connections can be. The more connections you have, the more chance for problems. Only use stainless or brass nuts on post connections, and once they're tight give them a spray with battery terminal corrosion preventer... basically a light spray wax that seals the connection against air/ moisture.

 

Ditto what 83 van said. No you don't need boat/deep cycle batteries. We never use them (ever) in ambulances and have no problem. What kills our batteries is alt. going out from high load!

Even the "cheap" 2 battery switches wire the same as K-H!


Rod

 

We don't use deep cycle batteries on our ambulances either - or our engines or tank trucks. Those all get started and run the whole call until returning to the barn. They are not discharged all the way ever.

Regularly discharging a regular battery will make it fail quite soon. That's what a deep cycle battery is for.

 

see my other problem is i have a camper that i pull, i want to put the switch on battery 2 for when the camper is parked, then swap back to battery 1 to restart. i will not have deep cycle batteries right away but i intend to go that route at a later date when i have the funds to do so, i am going to put the second battery on the passenger side so it won't be real far apart i just need to figure out where i want to mount my switch. i plan to mount my switch on the interior so that takes out some of the problem of corrision on the multiple connections.