Thread: need to tap into "true ignition source", have diagram, wondering what fuse is best?

Not that using IGN is the way to do it (search for UIBI and mp3car if you want to find a better method), but probably any fuse 1 thru 8.
Else 11 thru 16 if you want paralleling (interconnection) when also on ACC, but do NOT want the batteries paralleled for cranking (but with a 200A interlink, I usually recommend paralleling - ie, add the cranking/starter circuit to the isolator).

Whichever case, I'd go for the higher rated fuse circuits, but ensure you have spare fuses and can change else disconnect the relay.

Originally Posted by OldSpark

Not that using IGN is the way to do it (search for UIBI and mp3car if you want to find a better method), but probably any fuse 1 thru 8.
Else 11 thru 16 if you want paralleling (interconnection) when also on ACC, but do NOT want the batteries paralleled for cranking (but with a 200A interlink, I usually recommend paralleling - ie, add the cranking/starter circuit to the isolator).

Whichever case, I'd go for the higher rated fuse circuits, but ensure you have spare fuses and can change else disconnect the relay.

I'm looking to have both batteries running in paralleled when the alternator is running, but when not, only the rear battery will draw power (to keep my starter battery safe). Will fuse #1 work?

Then if you have a charge light, search for the UIBI - it's the best battery isolator for most applications with none of the drawbacks of voltage-sensing or "smart" (LOL) isolators.

The UIBI is merely a relay controlled by the charge light circuit so it does exactly what you want.

Note that some alternator charge-light circuits may have difficulty energising relays (and may be damaged), and many alternators - actually their regulators - may likewise have difficulties providing the 1A or 2A etc required for large relays (isolators) - eg, 200A and above, In the latter case, a normal 30A relay or smaller can be used as a buffer (the charge lamp energises the small relay which in turn energises the main isolator, and any number of isolators).

Of course the isolator will be connected between the batteries and have a fuse or breaker at EACH end close to each battery (unless, perhaps, they are next to each other).

There should be some (old?) indicative diagrams with my mp3car UIBI posts.


If the UIBI or voltage sensing isolator is used, the IGN circuit is irrelevant.

Originally Posted by OldSpark

Then if you have a charge light, search for the UIBI - it's the best battery isolator for most applications with none of the drawbacks of voltage-sensing or "smart" (LOL) isolators.

The UIBI is merely a relay controlled by the charge light circuit so it does exactly what you want.

Note that some alternator charge-light circuits may have difficulty energising relays (and may be damaged), and many alternators - actually their regulators - may likewise have difficulties providing the 1A or 2A etc required for large relays (isolators) - eg, 200A and above, In the latter case, a normal 30A relay or smaller can be used as a buffer (the charge lamp energises the small relay which in turn energises the main isolator, and any number of isolators).

Of course the isolator will be connected between the batteries and have a fuse or breaker at EACH end close to each battery (unless, perhaps, they are next to each other).

There should be some (old?) indicative diagrams with my mp3car UIBI posts.


If the UIBI or voltage sensing isolator is used, the IGN circuit is irrelevant.

Not wanting to do this UIBI method, although it may be favorable.

For convenience sake, I just want to use an add-a-circuit and plug into an existing fuse slot. If I go with #1 (ignition coil) it should work fine, correct?

Just to make myself clear:

- Batteries should be parraleled when vehicle is running, only rear battery is used for powering components in ACC or off position
- When vehicle is not running, only the rear battery should put out power to components (isolator kicks in)
- I am using a Stinger SGP32 200amp relay-type isolator
- To make my life easy, I want to tap into an existing fuse spot with an add-a-circuit (link) to draw from 12V ignition source

the fuse box under my hood might be more suitable...take a look at this diagram:



#4 is ignition switch!?

Btw does it make any difference if i am grounding straight to the battery versus the chassis?

You are repeating the same thing, ie:

Originally Posted by doncarbone

I'm looking to have both batteries running in paralleled when the alternator is running, but when not, only the rear battery will draw power (to keep my starter battery safe).

If you want your 2nd battery to power its loads with the key in whatever position, then you'll have to add an appropriate relay to imitate IGN or ACC.
You have to decide whether to mimic the ACC (so the 2nd battery's loads are disconnected during cranking) or IGN (on whilst cranking, but off in ACC).
Or you can have both using 2 diodes - ie, ACC via diode and IGN +12V via diode to energise the 2nd battery's "load" relay.

But that is separate to battery isolation - ie, isolation of the 2nd battery from the first when not charging.


So, so you want the 2nd battery to be isolated from the first when NOT charging, or when NOT on ACC or IGN?


The Stinger SGP32 is merely a relay.
How you control it is up to you.
If you use IGN +12V, understand that the batteries will be paralleled when cranking (that's better for the batteries, but the interconnect has to handle the current).
And for both IGN & ACC, if you forget to turn off...

To make a UIBI, all you do is connect the SGP32's "true ignition source" to the charge light circuit instead.
That's usually easier to wire since the isolator (SGP32) is normally close to the main battery as is the alternator, whereas some fuseboxes are in the cabin.
And it's fully automatic - if your vehicle is not charging, your batteries are isolated irrespective of the IGN-KEY status.

Note that Stinger's SGP32 documentation does NOT show the fuses at each battery end (though they may mention it). (They should be shot for that diagrammatic omission!)


And what relay are you using for isolation of the 2nd battery's load, or are you confusing the normal inter-battery isolator with your added load isolator (ie, ACC or IGN)?
Normally people use low voltage cut-outs to protect the 2nd battery from its loads if they are not turned off by radios (eg, amps) etc.
That's probably better in your case because if you have both the battery isolator and load isolator controlled by IGN or ACC, then if you forget to turn off, you'll have 2 flatteries.



If you decide to go with IGN or ACC for either or both, then chose any circuit as I described (ie, the upper group seems to be IGN +12V, the middle group seems to be ACC +12V).
If using a particular circuit pops the fuse, then change to another.

Note that the the 2nd battery and its loads will NOT be using any of those fuses. Those fuse circuits are merely to provide whatever source you want to energise the SGP32 etc.

Andf I can't find any info on the SGP32's coil current, but I'd assume ~2A.

I want the 2nd battery to be isolated when not charging. I do have appropriate size fuses before both batteries.

Ok...

So what isolator are you going to use?
IE - what circuit to control your relay (the Stinger SGP32)?