DC to DC MPPT Charger to Ignition

[zkywelder]

Under the hood, in my engine fuse compartment box, there are three different fuses that has Ignition label on it. I am not sure which one is a proper to use. I prefer not to connect to the alternator as it would void my alternator warranty if I splice the cable. Plus, I plan adding a manual switch from driver side so that it won't charge my batteries until I flip the switch on.

Ign-En
Ign-A
Ign-B

 

[MichaelK]

What exactly are you trying to accomplish here? Is your goal to charge your off-grid batteries from the engine alternator? Most likely what you would want is a circuit that has 12V power only while the engine is running. That way loads won't drain your starter battery when you're parked somewhere.

You can take a voltmeter and measure circuit by circuit till you find one that has power only with the key turned to "on". Most likely you'll want that one that has the highest amperage rating.

 

[HRTKD]

Are you trying to find an ignition circuit so the DC-DC charger knows when the vehicle is ON?

 

[camelCase]

You need a test light or voltage meter to verify the circuit you want to use is hot only with the key is in the on position.

What you want to do is to identify all the fuses that have zero volts with the engine off. Then turn the key on and check all those fuses and note which ones have power. Then go turn the key to the ACC position and go back an verify that the power is off on the one you want to use. You want one that goes off immediately when the key is off and which does not come on in the ACC position.

Here's an easy way to tap into a fuse instead of splicing into your factory wiring harness:

https://www.autozone.com/electrical-and-lighting/fuse-and-accessories/p/bussmann-atm-add-a-circuit-fuse-tap/32416_0_0

 

[zkywelder]

You need a test light or voltage meter to verify the circuit you want to use is hot only with the key is in the on position.

What you want to do is to identify all the fuses that have zero volts with the engine off. Then turn the key on and check all those fuses and note which ones have power. Then go turn the key to the ACC position and go back an verify that the power is off on the one you want to use. You want one that goes off immediately when the key is off and which does not come on in the ACC position.

Here's an easy way to tap into a fuse instead of splicing into your factory wiring harness:

https://www.autozone.com/electrical-and-lighting/fuse-and-accessories/p/bussmann-atm-add-a-circuit-fuse-tap/32416_0_0

Thank you! That's exactly the answer I need. I'll come back with results in the next day or two.

 

[Bud Martin]

So how much current is the DC-DC charger will be drawing? 40 ~ 50A?

 

[zkywelder]

50A. I am considering returning it and get 30A. I have a weird feeling that 50A might be too much. I did upgrade my alternator from 105A to 145A. It is smooth like butter, and it idles exactly like 105A alternator. Crazy. Glad I found a good quality alternator. So it should handle the load rather well but I don't like the idea of "quick charge" because quick charge kills battery faster than normal standard charge. I have 280A battery, mind you. But same time, it's like... whatever because what I got was mismatched. Two cells reach to same 3.6v while two other cells reach to 3.5v. Go figure, gotta love China. More info here.. It is top balanced and working properly.

Overkill bms + 280amp battery issues

Hello, I recently acquired 4 - 3.2v 280amp (EVE), with overkill BMS. I also got NOCO Genius 10amp 12v battery charger. The overkill setup is default. The only changes I put in is the capacity (280amp), and cycle capacity(224amp). I don't understand cycle capacity. I don't want the battery...

diysolarforum.com

 

[Bud Martin]

50A. I am considering returning it and get 30A. I have a weird feeling that 50A might be too much. I did upgrade my alternator from 105A to 145A. It is smooth like butter, and it idles exactly like 105A alternator. Crazy. Glad I found a good quality alternator. So it should handle the load rather well but I don't like the idea of "quick charge" because quick charge kills battery faster than normal standard charge. I have 280A battery, mind you. But same time, it's like... whatever because what I got was mismatched. Two cells reach to same 3.6v while two other cells reach to 3.5v. Go figure, gotta love China. More info here..

Overkill bms + 280amp battery issues

Hello, I recently acquired 4 - 3.2v 280amp (EVE), with overkill BMS. I also got NOCO Genius 10amp 12v battery charger. The overkill setup is default. The only changes I put in is the capacity (280amp), and cycle capacity(224amp). I don't understand cycle capacity. I don't want the battery...

diysolarforum.com

That "Bussmann ATM Add-a-Circuit Fuse Tap" is not going to cut it, it is only rated at 10A, you need to get good size wire and proper fuse size to tap into the output of the alternator to feed you dc-dc charger. What does the user manual say about wiring of the dc-dc charger to the car electrical system?

 

[zkywelder]

I don't think you understand what my intent is. It is not connected to the battery. It is connected to the alternator fuse box. This is a mere data driven wire to tell MPPT to turn on or not based on whenever the alternator is running. It only needs 16-18awg wire, nothing more, nothing less as the manual said.

Hence, my thanks to camelcase. He gave me answer.

 

[A.Justice]

Adding a switch to that sense wire is a good idea as well. It will let you cut off charging in hot, still conditions, like traffic, or if something happens (50a is a good bit of current, and a loose connection could cause a problem eventually). It could be a lifesaver to shut charging off while the vehicle is moving.

I assume you have the Renogy 50 amp MPPT model. If 50 amps is too much, they have a 40 amp model that can also do 20 amps with an external sense wire and switch. Their regular DC-DC chargers, without MPPT, all have the half amperage option. I think they also have a 30a/15a, and a 20a/10a unit.

 

[Bud Martin]

I don't think you understand what my intent is. It is not connected to the battery. It is connected to the alternator fuse box. This is a mere data driven wire to tell MPPT to turn on or not based on whenever the alternator is running. It only needs 16-18awg wire, nothing more, nothing less as the manual said.

Hence, my thanks to camelcase. He gave me answer.

OK, I understand what you are trying to do now.

 

[Tedski]

Adding a switch to that sense wire is a good idea as well. It will let you cut off charging in hot, still conditions, like traffic, or if something happens (50a is a good bit of current, and a loose connection could cause a problem eventually). It could be a lifesaver to shut charging off while the vehicle is moving.

I assume you have the Renogy 50 amp MPPT model. If 50 amps is too much, they have a 40 amp model that can also do 20 amps with an external sense wire and switch. Their regular DC-DC chargers, without MPPT, all have the half amperage option. I think they also have a 30a/15a, and a 20a/10a unit.

Have a quick question? If you place a switch in the 12 volt signal wire, to be able to turn the dc dc charger off while you're driving can you turn the charger back on (while driving) without damaging either the house or starter batteries?

 

[camelCase]

Turning it on while driving wouldn't hurt anything. It would be just as if you turned on all the accessories at once. The main issue is that a heavy load on the alternator could cause it to overheat, especially if you are sitting for an extended period of time in traffic at an idle while the charger was trying to pull it's full 50 or 60 amps (it won't be 100% efficient). In that case it might be a good idea to have a manual disconnect switch.

 

[Tedski]

Thanks for the input. I just had the alternator rebuilt and was surprised to learn form the shop that did it almost all OEM alternator actually pull about 25% less amps than what the manufactures publish. I like the idea of the switch. It's an easy addition and gives a little cush for the charger and alternator. HAGD