Battery Isolator

**WebDog** · 04-12-2005, 12:29 PM

Well the idea is with those relays is to have a 3 way switch so one way is always charge both when acc is on, then their is a off, and then their is a always on.

So it would work just like a isolator, if i found a way to make the relay swtch only when engine is on.

Right now with out any "protection" i just have a double capacity battery, so i should be able to run the audio same amount of time as before and not have a problem since before it would still start, barely.

**WhiteRabbit** · 04-12-2005, 06:54 PM

I dont really understand the way you have your three way switch wired up.

But I definitely understand the desire to want to have a good system of isolating the rear without using diodes allowing me to run the secondary battery dry but not the main. did your wiring scheme solve that problem? and if so, could you re explain it? I didnt quite get it.

**WebDog** · 04-12-2005, 08:22 PM

Heres what im thinking:

Switch position 1:
Relay closed when engine on. Both batterys connected only when engine is on. Not via acc.

Switch position 2:
relay open all the time. Both batterys never connected.

Switch position 3:
Relay closed all the time. Both batterys connected all the time.

**n8scstm** · 04-13-2005, 12:27 AM

The only problem with using relays rather than diodes is that if you have a dead aux battery and try to start your car, when you turn the key and start cranking the relay will close. Then you'll be trying to recharge a dead battery and start your car at the same time. This may not always work. Also, there maybe be a voltage drop cased by the starter on the aux battery. Maybe you could make a circuit that would close the relay after a few seconds of the engine running. Not instantaneously.

**WhiteRabbit** · 04-13-2005, 02:11 AM

n8, youve touched on subject #2 that I've always found very, very bothersome, and have never found a good solution for.

the timer isnt too bad an idea. complicated, but not a bad one. do you think its possible to achieve the same performance with a simpler technique?

webdog, I actually ran a more primitive form of your solution for awhile. Id be willing to bet that there are dozens of members on this board who do the same, run a switch. I got tired of it, personally. its ugly, its extra work, switch positions have to be memorized, the switch can't be forgotten upon vehicle exit or else bad things may happen, etc etc etc. the attention to detail just isn't there!

so that leaves us with the goal of designing basically a diode isolator without the voltage drop. not an easy task! the switch is simple, easy, and it works. but is not elegant.

**n8scstm** · 04-13-2005, 01:42 PM

Originally Posted by WhiteRabbit

n8, youve touched on subject #2 that I've always found very, very bothersome, and have never found a good solution for.

the timer isnt too bad an idea. complicated, but not a bad one. do you think its possible to achieve the same performance with a simpler technique?

That's the only thing I can think of. I know it's complicated which corellates to less reliable. That's why I said screw the voltage drop and went with the diode isolator. It seems to work fine except that my main battery seems to discharge rather easily but I think that may be due to it having been through Hell and back. It's an optima so I think I will take it back to Costco and try a new one. The aux battery will go forever, which is the reason that I believe the problem isn't due to the voltage drop.

**WhiteRabbit** · 04-13-2005, 03:45 PM

id love for you to reopen this thread in a couple months after it dies. You would be able to answer if getting the new optima cured slow starts, and then also be able to answer if you can sit in the car for an hour or so listening to music, if you can easily start the car and if it starts quickly. I would like to know!

**WebDog** · 04-13-2005, 03:54 PM

Ill have to work on my relay idea, A time delay wont be to hard. i just need to find a constant IGN wire thats not on unless the engine is on.

So in normall operation it works just like a isolator except both are connected when engine is on.

The switch would only be for manual overide.

**n8scstm** · 04-14-2005, 12:20 PM

Originally Posted by WebDog

Ill have to work on my relay idea, A time delay wont be to hard. i just need to find a constant IGN wire thats not on unless the engine is on.

So in normall operation it works just like a isolator except both are connected when engine is on.

The switch would only be for manual overide.

On old cars you would take a lead from the distributor for this, so on yours, I bet you could find a wire like that around the coil packs.

**n8scstm** · 04-14-2005, 12:23 PM

Originally Posted by WhiteRabbit

id love for you to reopen this thread in a couple months after it dies. You would be able to answer if getting the new optima cured slow starts, and then also be able to answer if you can sit in the car for an hour or so listening to music, if you can easily start the car and if it starts quickly. I would like to know!

As long as I'm not drawing any power from the main battery I can listen to music for hours. And the truck will start fine. If I'm doing it with the doors open though, and the dome light on, then I will get a slow start. I really think it's just the battery. I have treated it badly though the buildup of the truck. Shorted it a few times and even hooked it up to a cheap, dirty battery charger many times to listen to music while I was building the truck. I would keep the amps up high on the charger or the radio would distort. I'm sure that damaged the battery quite a bit.