broncobilly

I am thinking of using a marine battery switch in order to run two batteries in my 1st gen Cummins W250. I know a lot of members here are also members of the Pirate4x4 site, so you may be familiar with this setup. I am going to be using 1/0 welding cable, along with an isolator. Ragarding the isolator (for those that have done this mod), I assume that the amp rating on the isolator needs to be the same as the alternator? This setup can be viewed here at the Pirate site: http://tinyurl.com/mbjl2 Also, I plan on using this battery switch sold be West Marine: http://tinyurl.com/psd27

Jim Lane

That is a nice switch; most of them do not have the ability to parallel the batteries but to only select between.
The only concern with a switch is you would not be charging both batteries from your alternator except for when it is in the combine position, (which most likely you would not be in) but only the one that is in service at the time. If you didn’t alternate them you could be caught with a dead battery when you needed it the most.
You could use the switch in addition to a diode isolator (but I would recommend using a Schottky Diode Isolator to minimize the voltage drop) and maintain both batteries or use a set of relays or contactors and control them with a small switch.
I am using a Sure Power Separator and controlling 3 batteries in my truck.

Also be careful where you mount the switch because all of the battery current is present at the switch and could be dangerous in case of an accident. Most people mount them on the left side of the seat on the floorboard by the door.
In my case I would have around 4000 amps to burn something.

http://www.surepower.com/separator.html
http://www.surepower.com/pdf/separatorinterconnect.pdf

Some basic isolator diagrams.
http://www.surepower.com/pdf/180119A...0isolator'

Here is a post about my system.
https://www.dieseltruckresource.com/...ad.php?t=92713

Jim

broncobilly

Jim,
Thanks for the input on my dual battery post, as well as the SurePower links! That 200 amp serparator SurePower makes, looks like it would work good with my dual battery setup. I am thinking of maybe ditching the Marine dual battery switch, for the reasons you mentioned.
One problem I felt with the Marine switch is: my dual battery setup consists of two Red Top Optima battery's, rated at 850 CCA, so combined CCA would be 1700 CCA. The Marine switch I have is only rated for 1500 intermediate amps, and 300 continious amps. So, I figured if I needed the two battery's on startup, the marine switch would be under-rated at 1500 intermediate amps? I know I am probably wrong here on my logic, as I believe your dual battery system amperage is influenced by the amperage rating of your alternator? Also, you would only need the two batteries on startup, in the event the your main battery was drained to the point where it wouldn't kick over the engine.

Regards,
Bill

Jim Lane

Bill,

I think the switch would be OK to use because even though you will have a combined 1700 CCA the starter will still always be connected to the main battery and when they are paralleled you will only be connecting 850 CCA to the already existing 850 CCA.
Now if you were connecting the load to the common terminal of the switch so you could select #1 or #2 or #1 & #2 then there might be a problem but only if you could actually draw in excess of the 1500 CCA with your starter.

I could see stone cold in Alaska 30* below 40wt oil in your crankcase, grid heaters not working and someone cranking to get it started.
Maybe..

You would only need the 2 batteries for starting, true but with a switch you would need to alternate them to keep them both charged unless you used an isolator to do this automatically and the switch for the purpose to parallel.


Jim

Timmay2

Well the purpose of the isolator is to keep the 2nd battery from draining when they key is "off".

When you turn the key on, the isolator should allow both batteries to work/crank/charge when the engines running.

It only seperates the two when you kill the ignition..

No need for any sort of switch outside of hooking the isolator up to your ignition.

jrs_dodge_diesel

Timmay, I think you have that backwards. We use isolators on some of our small rescue boats. They have the main batteries (2) for engine starting and a 3rd battery for running the electronics. The 3rd battery is isolated with a very large diode (only lets electricity flow one direction, like a check valve). It is setup so that the 3rd battery only runs the electronic equipment and does not start the engines. The diode prevents the starters from drawing power from the electronics battery but when the engines are running the alternator can charge the electronics battery.

Jim Lane

It also removes the nasty spike and voltage drop on the auxillary battery caused by the starter motors and protects the sensitive electronics.
The OEM dual batteries on my old 6.2 would wreak havoc and reset my 800 MHz communications set every time I would crank with a cold engine.
I cured that with two 1 farad capacitors and a diode in the power line to keep the line stable.

JRS, what type of battery supplies the electronics?
deep cycle or regular starting type?
12, 24 or 36 volt.
Jim

jrs_dodge_diesel

AFAIK the entire system is 12 volts. The boat has twin outboards. It has 2 batteries to run the engines. Either battery can run the boat alone and start both engines, or they can be used together. The 3rd battery is a deep cycle, like the other two are. All three are the AGM type battery, since the batteries are locating in a compartment inside the main cabin of the boat.

Jim Lane

Nice looking boat,
I did not know you were referring to an outboard, are the motors militarized in any way or they just off the shelf stock? how do they ride in rough water?
How far out will they take these from shore?

They might be able to slip in 24 volt systems though.


For some reason I thought you were talking of something in the 40’ Motor Lifeboat class.

Jim

Timmay2

In a setup like that though you drain your original batteries with the accessories.. thought the purpose of an isolator is to run electronics without draining your main starting batteries. IE completely breaking the circuit between the main and the secondary batteries when the vehicle is not running.