relay or isolator

Problem: I have a 220amp HO Alternator & a different battery in my engine compartment than the battery bank in my vehicle that powers my radio. I personally want them completely separated at all times so my interior oem components do not see a voltage drop (no dimming). (I also dont want them discharging each other when not in use) Alright I've done alot of research on both but each has it's pro's and cons. Now The Isolators with the separate Diodes and no moving parts is the technology that I need. One that will charge my Main starting battery, and my battery bank in the back. Basically I want my radio pulling from my battery bank and not front AT ALL with car on or off. But with the voltage drop that's not so efficient of an Isolator to use. Is there any other way to make this to happen? my theory behind this is I want to keep my battery bank separated from my front battery so my light's and other electrical components will not suffer any voltage drop aka dimming since it is not being used for the massive current draws. Does that sound about right? or is it actually more efficient to just use a PAC-250 relay and add my cranker into the mix of powering the system? Let me know what you think! thanks!I can't hear you!

Here we go again! The diode is the only way to do what you want. With proper distribution and design you should not have the dimming troubles with a relay. But for reasons unknown, you chose more batteries rather than a suitable alternator (despite your amp apparently producing well over 30% less output on batteries!!!). FYI - As I wrote, the norseman wrote more batteries for SPLs - the suggestion being a bigger alternator for road use.   Granted, later he did say bigger battery for road use (which is incorrect), but at least he got the SPL right - except when amp output varies with voltage. Don't forget to increase your alternator voltage if you use the diodes (ensure the S wire if used is on the battery side). Don't exceed the diode rating (usually >100A is difficult to get, and they're probably gonna be expensive). And make sure they are well vented - they get hot wasting all that power LOL! Diodes - the worst choice of them all. Ha!

We meet again... alright alright, I think I'm just going to go with the PAC-250amp relay, because with the isolator I would have to get the Isolator AND a voltage module to charge at 15.3V just to have it set up a certain way, and I dont have certain money... sooo lol I have decided to go with the PAC AS long as The batteries do not discharge eachother when car is off, I'll be fine for now. Thanks again ole spark!!I can't hear you!

As long as you switch off the PAC, the batteries will be isolated (unless its contacts have fused). I have described in your other thread & elsewhere how to do this automatically for no cost. That does not mean that the batteries will not flatten - get a dash-voltmeter for that. The 15.3V voltage module should cost you about 10c, or 20c with "reversible redundancy", but that depends on your alternator type. (If it's a single wire D+ type, it won't work unless you hack internally.) However I have no idea why you would want 15.3V unless perhaps you are using diodes to all batteries, or you like AGM thermal runaway. But I have little doubt someone has told you that's what you need. For someone with a limited budget, I reckon you will be spending way more than you have to, or should! How are the Florida lads going wrt to answering those questions....? Stay with them - that way you'll have consistent advice.

oldspark wrote: As long as you switch off the PAC, the batteries will be isolated (unless its contacts have fused).

Come onnn so when the car is OFF (no key) with a relay all of the batteries (even the engine battery) will be connected in parallel?? Only when the key is in the "on" position they will be isolated? Just questions #1 and #2 "yes" or "no" I tried to make those questions as simple to answer as possible lol 1. 2.I can't hear you!

No. No.

oldspark wrote: No. No.

PERFECT! So only when the engine is RUNNING will the batteries be connected in parallel and charging from the alternator, correct? 1. (yes or no) lolI can't hear you!

No. My "ultimate intelligence battery isolator" solution only connects the batteries together when the alternator is charging.

alright what is the name of yours, or a relay that you know works exactly like yours?I can't hear you!

It has no name. Any relay. The PAC you have should be ok.