AGM BATTERY CHARGING - ALTERNATOR VOLTAGE BOOSTER

Yep, here it is in my truck. It works great. I've had it working for about a month.

 

So am I understanding that now you’re sensing voltage from the new (previously unused) circuit instead of the original sense wire?

 

Yep, this is how I did it.

 

Ok cool. I think I’m gonna try to double stack them so I can use the original voltage source. If I can’t make that work I’ll try you method. Thanks for answering my questions.

 

I tried to figure out a way to do that. It’s impossible unless you can cut away plastic, cut terminals, and solder the wire to a terminal.

 

Yea I had a feeling that would be the case. Have you checked your charging voltage yet?

 

It’s about 14.6 to 14.7 when fired up from cold and drops down to about 14.1 when warmed up, according to my Scangauge.

 

Interesting. I thought it needs to be 14.7v all the time. If it drops to 14.1v rather quickly, is the battery still not fully charging?

 

I’m no battery expert, but I think it needs the higher voltage to charge it and then it cuts the voltage back to maintain it.

 

Yea I think that makes sense. I thought you meant when the alternator warms up the extra resistance in the windings drops the voltage (even if the battery is not fully charged yet).

 

I ordered a GM diode from RockAuto. Got three of them shipped for $12.

https://www.rockauto.com/en/parts/acdelco,12135037,a/c+compressor+diode+connector,47621

 

I did this mod using the exact same method as @Muddinfun about 10 days ago(??), using the same fuse location which was also empty on my truck. It's been working great and with the expected (same) results. I'm measuring voltage at the obd2 port using the torquepro app. My max voltage has been 4.6 but it's the same basic idea.

I haven't done anything to actually prove the fuse would blow (like deliberately shorting it out) but there isn't any reason it shouldn't. With everything in place I get the voltages described. If I pull *either* the fuse, or the diode from the, I get a battery charging trouble light in the dash so I know the current is flowing through both.

Just in an abundance of caution I might go back and fill in the unused slots with epoxy or something but since I'm the only one that does stuff to my truck I'm not too worried about it.

 

I did the mod tonight and the voltage at the starting battery went up to 14.74 volts with a 1 amp diode.A pair of fuse taps cost $4.32 and the diode was $3.99. I already had shrink tubing and the sealed butt connector. All in was $8.31 for this mod plus 20-25 minutes of my time, mainly making sure of how I wanted it to layout in the fuse block.

I'm using a CTEK D250SA DC/DC charger which has the capacity to charge the house battery at 14.4 volts. By attaching a small wire to ground, it increases the output voltage to 14.7. When I attached the diode harness to the fuse block the start up voltage was 14.94 at the house battery. When it's not on the verge of dark tomorrow I'll go through a startup voltage check and make sure it's coming down to the correct range.

UPDATE 4/18/20: Charging voltage to the second battery is regulated by the DC/DC charger profile irrespective of the alternator. However, it does charge the house battery at 14.94 at startup and drops quickly to the maintenance charge at roughly 13.8 passing the charging phase at 14.7 volts.

The charging voltage on the starting battery was similar at 14.9 and then it settled into a steady 14.72 once the starting battery had been topped off. This is working exactly as hoped

 

Not sure if this will work for the older Tacos, Dirty Parts in California might be able to build one that works. Installed this in my 4th gen 4runner yesterday, we'll see how it does.
https://www.dirtyparts.com/store/detail.cfm/ALTERNATOR-VOLTAGE-BOOSTER-TOYOTA/pid-161838

 

I have had the diode for several months now, I have found one issue related to my dometic fridge/battery set up. I have it set up to charge the dometic battery when truck is on and in turn, runs the fridge. I keep blowing the fuse that is in the power cord to the battery - 20amp, glass fuse.

I am guessing this is due to the cold start volt @ ~14.8-9

Any thoughts, besides keeping it unplugged until the truck is started - and then plugging it back in?

Mike

 

I was hoping to be able to do the fuse tap method until my hkb booster gets here but I have a 10amp fuse in that location and it’s labeled Air Pump HTR.

 

You should be able to still do it. Just find a constant power source and leave that fuse in the lower part of the tap, put the 7.5 amp on top and the diode over in the Alt-S slot in the other end of the tap.

 

I was thinking that would work. Or I have an aux fuse block with 10 open circuits that I could probably use. Although I’d have to run the setup out of the fuse box. My hkb booster is currently in customs so I’d rather not cut my fuse box for a solution I only need for a couple days.

 

If it's literally a couple of days, forget about it. Your battery will never know the difference over its lifespan.

 

I was considering that too haha. My battery now is complete junk, I’ve just been using my jump pack when the truck won’t start. I don’t have to go anywhere until next Monday so I think I’m going to just keep watching the tracking on the booster and come Saturday if it isn’t here I’ll just put the battery in without it.