The Official Dual Battery Thread

[zberger]

This is what I used..

Works awesome, easy to install.. and cheap!

I actually got the cheaper one.. which I will also post, the boat I used it in had a smaller alternator..

http://www.napaonline.com/MasterPage...ttery+Isolator

And since that link sucks.. I used the 34 dolla one..

Worked great all summer.. and hopefully when we pull the boat out here soon we'll be good to go!

[djhuff]

I have one of my more electrical savy friends looking into a delay circuit to put in line with the ignition circuit to the relay. Looking at about 10 secs. I'll let you know what we come up with.

[Diesel]

Cool, keep up posted.

[JimN]

"Pulse Stretchers" are easily available from a lot of 12V suppliers. They're used in alarm and audio systems and one type I have seen goes from .1 sec to 10 sec and their other model goes from 5 sec to 50 sec. IIRC, the company is PAC. This circuit is also called a 555 timer, because that's the number of the chip used. TI makes them and I would think other companies, too. Timer circuits are in every basic circuit design book.

[Diesel]

"Pulse Stretchers" are easily available from a lot of 12V suppliers. They're used in alarm and audio systems and one type I have seen goes from .1 sec to 10 sec and their other model goes from 5 sec to 50 sec. IIRC, the company is PAC. This circuit is also called a 555 timer, because that's the number of the chip used. TI makes them and I would think other companies, too. Timer circuits are in every basic circuit design book.

I guess we need to determine the amp draw to keep the relay engaged, which could be a challenge for many timer circuits. I have never seen a spec on the BW3098 so I guess I will have to get out the fluke when I get a chance to measure current draw. If I had to guess I would pu it in the 1-2amp range.

[JimN]

The current isn't really much of an issue since a Bosch style relay (20-30A) could be used to latch the solenoid and a Bosch style (either that brand, Potter & Brumfeld, etc) draws about 150 mA, easily handled by the timer circuit.

[Diesel]

The current isn't really much of an issue since a Bosch style relay (20-30A) could be used to latch the solenoid and a Bosch style (either that brand, Potter & Brumfeld, etc) draws about 150 mA, easily handled by the timer circuit.

True, true............

[bikeman]

could you please e-mail me?

True, true............

Diesel, I have the same 95 Prostar 205 you used to have and would like to ask you some speaker placement/power questions. it seems you used to have components in the back, but your gallery doens't show if you had any others. Could you e-mail me at [email protected] or should i start another thread? any help would be appreciated.

thanks!
Chris

[Leroy]

Brian and zberber; These look pretty good and like they are meant for the purpose. I think Diesel is right this normally is not a problem.

I was concerned with the same thing. I used this instead of the relay. This combiner doesn't put the batteries in parallel until the motor is running, ie the alternator is charging the system. No chance of killing your starting battery with a drained aux battery. No switches needed, totally automatic and very simple to wire in.

[prostar205]

Well, after not listening to Diesel about the BW R3098 relay and using my Perko switch instead, I finally blew up the voltage regulator by attempting to start the boat with the Perko switch set to the OFF position. When you do this it grounds the negative side of your batteries directly into the alternator and blows the voltage regulator. I got that fixed for $40 and immediately went out and got the R3098 relay. I took the Perko switch out and installed the relay last night, along with the reworked alternator, and everything works great again.

Thanks again Diesel for this thread, it is a life saver.

You are the man!!!!!!!!!!!!!!!

[edwinfuqua]

Nice-simple dual battery set-up. I can only ask, if in ACC mode and your ACC battery goes dead; what happens when you start your engine and the dead battery is connected by the relay (contactor for high AMP service) when you try to start? At that point the dead battery is being charged by the starter battery. Or did I read your schematic wrong. The starter battery should be the only battery used when starting and then both batteries should get equalized by the charging circuit. Hmmmm.

Edwin

[edwinfuqua]

Just a thought, if using a SPST relay to isolate the batteries in the start and run positions, would it not be better to only select the start battery insteed of tieing two (ACC and Start) togather while starting? Start position should only select the start battery. In run position both batteries are used and charging. In ACC mode just the ACC battery is used. In start mode the main start relay would only select the start battery. Seems like that would take at least two contactors. Let me think upon it furthur.
Edwin

[edwinfuqua]

I was concerned with the same thing. I used this instead of the relay. This combiner doesn't put the batteries in parallel until the motor is running, ie the alternator is charging the system. No chance of killing your starting battery with a drained aux battery. No switches needed, totally automatic and very simple to wire in.

That's the ticket. Probally cheaper than a few relays, less relay knowledge and they work. I used one in a van and always had starter battery even when switch off and discharging the other playing the stereo. You might be able to do the same thing with 2 or 3 relays but the wireing could cause problems during installation.

[edwinfuqua]

I was concerned with the same thing. I used this instead of the relay. This combiner doesn't put the batteries in parallel until the motor is running, ie the alternator is charging the system. No chance of killing your starting battery with a drained aux battery. No switches needed, totally automatic and very simple to wire in.

When you use a battery isolator, relay or other system if you have two different size or type of battery eventually tied togather on one charging circuit you will have problems. The two batteries must be identical or you will have serious battery problems.

[edwinfuqua]

Anyone have a comment or answer on my above posted question???

Batteries under the same charging circuit should be identical. Don't mix deep cycle and starter batteries. Either run all deep cycle or all start batteries. I like the six-pack style for my boat. They are made to handle a lot of vibration and don't seem to kill off by discharging below 9 vdc like most standard car batteries. Deep cycle batts don't have enough start capacity for HP motors. What ever you do, if you have them tied in parrallel while charging make sure they are all identical.
Edwin