Phoenix Gold Phorum

HI Guys

I bought a dual battery isolator from a phorum member and wanna say thanks.

My question is this , I have an E30 BMW with battery in the boot. I want to put the 2nd battery in the boot as well.

Currently my cable layout is as follows.

Alty --4G---> Starter ---4G---> Firewall Block ---4G---> Battery

From what I understand I now need to do this

Alty --2G----> Isloator --4G---> Battery ---4G---> Starter and other electronics.

Poses a problem where I will now have 2 lengths of wire running down the car, one being from Alty to Isolator and the other in the reverse direction from battery to Front of car.

Is there any way I can get away with a single cable run and not 2.

Cool it got there I was wondering. Why is the 2nd run there?

if I mount the Isolator in the front of the car, I need 1 run to primary battery and one to aux battery (2 runs)

Alty -----Isolator =========> battery 1 and 2 , I can tap off primary battery terminal on isolator for starter and electrics. its the same circuit


If I mount isolator in the back of the car I need one run from alty to isolator and one from battery back to starter and fuse box

Alty ----front to back of car-------Isolator A -------> Battery 1 ----back to front of car----> Starter and electrics

You already have your alt wire to your battery in the trunk so you dont need to run another one.I think the manual figures you have the battery in the front so your good to go with the stock wire unless you have a big aftermarket alternator.

It also says that the wire from alty goes to centre pin on Isolator, this does not have power when the car is not running. The ECU and Starter are all connected to the same wire that runs from front to back at the moment, these cannot have no power when the car is not running.

So you have to take one from the isolator or primary battery. hence my dilema.

Yes i have a cable in at the moment, but the cable feeds the rest of the car as well, the fuse box and ECU and Starter are all in the front.

You take the wire that's coming from the front now that is connected to the battery and hook it to the center pin on the isolator and then connect the batteries to the other pins. The car will still have power to the front but the starter might overload the isolator this way without a dedicated wire to the starter for the high amperage to crank the vehicle. You might be better off using a relay for the second battery then you would not need to add any more wire to the front.PG made a relay for this that was automatic,it was model MBS115.

I am still confused, not sure why maybe if you could draw a pic of it I could see it better but I think you are overthinking things.

I have both batteries in my trunk as well but used a relay isolator. The smaller starting battery is always connected into the cars electronics/starter as well as the isolator but it is ALWAYS connected to the alt. The bigger stereo battery is only connected when the car is running and my isolator charging system sees that voltage is above 13v. The only modification I made was to add a switch that allows me to use both batteries to start the car in case the starter battery is low for some reason. I have 0 awg ran all the way down to the isolator and to both batteries.

A Relay would work easier as you have ahot side and a cold side for isolation.

If you check the PG manual for the Isolator it says that when the engine is not running the centre pin will have 0V, so I cannot simply connect the exsisiting cable to the isolator as the front electrics will then have no power.

So I have to wire from the positive terminal back to the front.

Hence the need for 2 cables. If I mount the Isolator in the front of the car I still need 2 cables , one to primary battery and one to Aux battery.

Hope that makes sense
trying to draw it out.

a gotcha..... So unfortunatly you find yourself at the same point I did, having already got the diode isolator, wondering why you are not going with a relay huh? This along with the voltage drop, idunno I would consider doing what I did and sell the isolator and going with what is easier.

I may just have to , will see if I can flog the isolator locally.......DOH !!!

I know it sucks, like I said been in that exact position. But I can say the size of the relay, the ease of use and low voltage loss is enough to make you forget about it sooner then later.

Here's the PG relay link:http://download.phoenixphorum.com/Manua ... ctions.pdf

interesting never seen one of those myself.

ttocs wrote:interesting never seen one of those myself.

It's a nice piece,fully automatic operation depending on the voltage.

yea I saw that I had to buy an extra module to do that, and wire in a switch to use both batteries. Anyone actually seen one?

I have a new one in the box I can get a picture of.

MBS pics

huh only 100amps but wish I knew about that when I bought mine.

ttocs wrote:huh only 100amps but wish I knew about that when I bought mine.

I wonder if it would be safe to run two in parallel...

should work.

stipud wrote:

ttocs wrote:huh only 100amps but wish I knew about that when I bought mine.

I wonder if it would be safe to run two in parallel...

It's good for 400 amp peaks.You could also use this as a trigger to operate bigger high amp relays.