house battery questions, charging, isolator? do I need one?

Itsavanman

Adventurer
Plotting out some stuff for my superu. while just using the starting battery to run things works as I keep a jumper pack ready and waiting, I'd like to install a small deep cycle to run lights, and do some other things like possibly a cooler. anyways, I already have an 8 gauge wire running for the amplifier. basically what I would like to do, is use this wire to be a 12v port on the trailer plug, run to the power port, as well as be connected to various LED's. anyways what I would like to do is run a 5 prong relay so when the vehicle is running it pulls from the regular battery / charging system, disconnects the deep cycle, and charges it. and once the vehicle is turned off the relay disconnects the wire from the regular charging circuit, and connects in the deep cycle. now with this setup all the batteries and ports share a common ground, which from what I've seen on most motor homes, isn't done. I can assume its because of backfeeding, or still drain the starting battery. or ? now I've never used a battery isolator could I use one for this particular setup? do I need one? will a simple diode do the trick? and if so where exactly would I put it? Also, as far as charging the deep cycle.. every battery charger ive ever seen has a option for deep cycle charging. I know to keep them happy they need a specific charging style, can I just charge off my alternator? or are there any cheap onboard charge controllers that run on 12v? or is it overkill? and finally since I'm putting increased demand on my alternator, and its got a bearing squeak, I plan on rebuilding it, and while I'm in there beef up its output. problem is. its a subaru alternator. anyone know if they make increased output kits for these? I don't want to spend over $200 for a new alternator, id rather tweak what i have..
 

john61ct

Adventurer
Called a combiner, ACR, VSR.

Should sense voltage from either bank so any charge source will feed both batts.

Ignition solenoid is cheaper, but only pertains to alt, which is usually a very minor source, compared to shore charging, solar, gennie.
 

Itsavanman

Adventurer
well for now, no other charging just the alternator. possibly solar in the future.. which I would make a stand to put it outside, and feed through a connector (rv 7 way under the hood or behind the front plate for winch power, and upgradable if I ever flat tow it to run the lights) the wire is fused at 30a so I was just going to get a 40a relay.. a 80-100a solenoid is overkill I think. no?
 

john61ct

Adventurer
If starter current passing through, 200+A.

And unless you drive all day Alt won't do much for a lead bank, LFP maybe.

But not a stock Alt setup in any case.
 

Itsavanman

Adventurer
I'm looking into an alt upgrade, and the battery is small (has to be to fit) looking at around 30AH and the upgraded alternators look to be in the 200a range.. that would charge it up quickly? seeing as its almost double. and no starter current would not be passing through this wire, its somewhere with the amp cranking about 25a and I don't plan on running the amp, and the camping gizmos together.. would either be lights or amp or winch. which speaking of which, how much amperage does the winch pull? and how much does a small 12v cooler pull? and whats LFP?
 

dwh

Tail-End Charlie
No need for all that complexity. Just wire the aux loads to the aux battery, and use an ACR like a Blue Sea or a Samlex to connect the aux battery to the engine battery when the engine is running.

When the engine is running and the ACR is engaged, power will flow to the aux battery and the aux loads. The loads will be powered by the alternator and the battery will charge.

When the engine is off and the ACR disengaged, the aux loads will run from the aux battery.

Only problem is if you use the same wire that feeds the amp, then when the engine is off, the amp will still be powered from the aux battery.

So put the ACR in the rear instead of under the hood. Tap off before the ACR to feed the amp so the amp is only powered from the engine (technically, the engine battery).



And any alternator will only produce what is drawn out of it. If your aux battery can only absorb 15a, then it will only draw 15a and even a million amp alternator would only produce 15a. Going to a bigger alternator won't make the battery charge faster.
 

Itsavanman

Adventurer
I could do it that way, howevr the amp has a remote turn on wire from the stereo, so its only on when the stereo is on, so really don't need to worry about that, but, it would be nice to have the option to run the stereo without the amp draining the starting battery, so, utilizing an acr, with the amp wire moved to the aux batt. everything still shares a common ground.. is that okay? that was my main question. also does an ACR do anything but connect in the aux battery? does it have any special guts like say a deep cycle charger? I see that they are voltage sensing, but why cant I just take the trigger side of a relay, hook it to ig+ so any time the key is on, the aux battery is not isolated. I think I just answered my own question, if the aux battery is low it will draw down the starting battery while trying to start the car, which could cause it not to start.. at least I think.. yeah I think I'm just going to look into buying or building an ACR.
 

dwh

Tail-End Charlie
I could do it that way, howevr the amp has a remote turn on wire from the stereo, so its only on when the stereo on

It would still be on when the stereo is on, but it would be powered by the aux battery when the engine is off and the ACR is disengaged.


so, utilizing an acr, with the amp wire moved to the aux batt. everything still shares a common ground.. is that okay?

Sure, as long as the wires are thick enough to handle the total load.


also does an ACR do anything but connect in the aux battery? does it have any special guts like say a deep cycle charger?

Nope and nope. Just a solenoid (heavy duty relay) with a little logic brain to sense rising voltage (engine is on, alternator is producing power) and engage the solenoid.



I see that they are voltage sensing, but why cant I just take the trigger side of a relay, hook it to ig+ so any time the key is on, the aux battery is not isolated.


http://forum.expeditionportal.com/t...ke-a-cheap-isolated-dual-battery-setup-for-50


I think I just answered my own question, if the aux battery is low it will draw down the starting battery while trying to start the car, which could cause it not to start.. at least I think..

No, it won't. It takes quite a while to move power from one battery to another. Tying them for a split-second before engaging the starter won't draw down the starter battery enough to notice.


yeah I think I'm just going to look into buying or building an ACR.

Buying yes, building unlikely.

A big dumb ignition controlled solenoid is called a "split-charge relay". That's the $50 isolator. My truck has that.

An ACR (automatic connection relay or automatic charge relay) is a big dumb solenoid controlled by a little computer brain.
 

Itsavanman

Adventurer
yeah I looked into a mini ACR their only like $50 which would work.. but the geek in me wants to build it, the circuit is actually really easy.. out of an arduino (lil teeny computer) like a raspberry pi if anyone has heard of that.. and said big dumb relay. mainly because I got it for other projects, and want to try and different program on it. the other way is a voltage theshhold like what turns your battery light on, with an output pointed towards a 555 timer (lil chip) set for one minute or similar IC. honestly the delay I think is whats the most important part, the voltage part I think is just so you don't drain both batteries if you leave the ignition on with the car off..... I like screwing with electronics, so, I still could go either way. another reason to build it, is to add a smart charge circuit if needed.. or just something to do lol...
 

Itsavanman

Adventurer
geeking even further.. voltage sensing can be done with a ziener diode (I think) basically a ziener diode is a one way voltage gate, unless the voltage rises above a certian threshold then it lets it through, thus triggering the "start countdown" signal to a timer, I think I can build one for about 5 bucks... To the lab pinky! lol
 

john61ct

Adventurer
Make sure your DIY fails open, isolated.

Sense V on both sides.

Put delays in to prevent chattering.

Better to just buy IMO.
 

rruff

Explorer
Plotting out some stuff for my superu. while just using the starting battery to run things works as I keep a jumper pack ready and waiting, I'd like to install a small deep cycle to run lights, and do some other things like possibly a cooler.

I'm going to have a pair of deep cycles that do everything including start the truck. Simpler.
 

Forum statistics

Threads
185,539
Messages
2,875,669
Members
224,922
Latest member
Randy Towles
Top