Off-Grid Engineering Dual Battery System Q&A

I see you have a 2nd gen... this thread explains the voltage upgrade for 2005-2015 Tacomas with the Alt S Fuse.

https://www.tacomaworld.com/threads/the-northstar-agm-battery-voltage-booster-upgrade.604478/

The MLACR and other smart relays directly connect and charge the batteries together therefore it is best they are the same type (AGM, etc) and same age. With the BCDC charger it doesnt matter what age or type the batteries are because they are independent from one another. The DC to DC charger regulates Voltage and current flow with different charge profiles based on battery type. Also has integrated solar controller.

https://www.youtube.com/watch?v=hcEMT6ucGZY

 

So are you saying that if I use a BCDC, then I will not need a MLACR?

 

Yes. They are two different ways to power an auxiliary battery.

MLACR directly connects your batteries and uses the alternator to charge both.

BCDC batteries are not directly connected. Main battery charges off alternator while Aux bat is charged through the unit. The unit can better taylor the specific voltage etc to the aux bat.

Only downside to the BCDC is that you cannot jump start yourself in the event of a dead main battery without popping the hood and using jumper cables. Unless you wire that up separately.

 

Taking measurements would be the way to go. I recall someone saying the group 35 was the only one that fit on the passenger side of the 2nd gen OR models. But who knows how many different options that guy tried.

Nope. I run dual AGMs tied together through an ML-ACR and charged via the trucks alternator (with a 0.5 volt booster).

So theres a lot of different and good threads on here, but some of the cliff notes:
- When the batteries are charged together:
Chemistry, aka battery type, matters a lot. Its pretty bad to combine different types straight up. They will all have different charge rates, slightly different resting voltages, etc etc. Its also not great to combine an old battery with a brand new battery.

- If the batteries are electrically isolated:
In your case it sounds like you want to use a DC-DC charger for the aux battery. So you could leave the stock battery in place and add a nice AGM (or lithium or whatever) for aux loads somewhere in the truck. The DC-DC charger gets its power from the stock battery and takes care of charging the new battery according to whatever battery type you set it to.

I went the route I did because it seemed like the simplest solution and I could self jump start myself.

A note about AGMs: due to the chemistry in the battery the voltage they need to be charged at is slightly higher than a normal lead acid. Thats where voltage boosters come in. 2nd Gen trucks (2005-15) use the Alt-s fuse circuit to monitor and control the voltage. The booster diode essentially make a small voltage drop in that circuit, so the truck sees 0.5 volts less than what the system is actually at. Therefore it compensates with an extra 0.5 volts higher from the alternator. (Hopefully that makes sense..)

A high output alternator only bumps up the power output, not necessarily the voltage.

Hopefully that gets you headed in the right direction

 

Thank you for this Zack, you read my mind. I need a new truck battery to replace my yellowtop. It is about 6 years old and starting to go. I want to go with most likely a redarc because I want to add the solar option. I don't have the electric knowhow to do the voltage upgrade to have my stock alternator keep up an AGM for my starting battery. Do you have any recommendations regarding a good truck battery to replace my yellowtop? I don't know if I should go with another AGM knowing this now. I was looking at the X2 power but I don't know if I am getting myself in the same predicament.

 

@SR-71A I also looked into the Voltage upgrade on the threads and most of them are out of stock.

 

Reference the thread I linked in post #621. Its a simple replacement of a fuse that tricks the alternator to put out the extra .5V.

HKB Electronics is the Australian company that makes them. They have an ebay store with everything in stock. You will want the MK2 or MK3.

https://www.ebay.com/itm/222643418070

 

Yup, @jcott329 is correct. Its a very easy upgrade (if you decide to go that route..) The Alt-S fuse in the engine bay fuse block (its a 7.5A fuse from the factory) gets pulled out and replaced with a unit like above. Biggest issue is waiting several weeks for shipping from Australia Though I have heard they've gotten better recently.

As far as what type of battery, I cant really make any recommendations. If you're just going plain old lead acid to start the truck I would probably say go with something that is readily available locally. Nothing fancy. Just in case it happens to crap out, you can easily get it warrantied. The X2 Power batteries are actually re-branded Northstar units.

If you plan on running solar, a RedArc with PV input sounds like the way to go

 

What is the difference between the MK2 and MK3? When I read the thread from crashnburn, he stated to watch out for over charging voltage.....
Will this work with only one AGM battery for now or do I need a dual battery before I install this?

 

Im still learning a lot about the subject so someone correct me if I am wrong but the MK2 is like the factory style Micro (mini low profile) fuse and the MK3 is a Mini style. They are interchangeable and perform the same function. These provide a fixed ~.5V increase over stock which puts it in the correct range for an AGM. Its always a good idea to measure your own voltage before and after to confirm but .5V should not over charge an AGM battery single or dual. It will simply charge it closer to 100%. I have a single AGM right now and plan to add the fuse before going dual AGMs in a year or two. It would only be an issue if you replaced the fuse with a lead acid type battery because they require a lower (stock) voltage to charge.

Here is an image I found showing the micro vs mini style of fuse. They both fit the same and should work in the 2005-2015 Tacomas the same. For what its worth I ordered the Mini (MK3) because it was a few dollars cheaper.

 

Although every alternator may have slight variances... if our 2nd gens charge 13.9-14.0 stock for the lead acid battery, with the MK2 or MK3 it will charge the AGM at 14.4-14.5V which is in the ideal range.

 

Yep, all covered here: https://www.tacomaworld.com/threads/the-northstar-agm-battery-voltage-booster-upgrade.604478/

 

@crashnburn80
I just replaced my 24f stock battery to an InterstateH6(48) AGM 36 battery from Costco. What do you recommend for fixing the alternator voltage?

Is it only fixable via ECU tuning?

 

Nobody has proved a viable solution to adjust the ECU regulated voltage for 3rd Gen. Some guys reached out to tuners but didn’t get any traction and others tried Techstream with no luck. You will need a wall charger for proper AGM maintenance charging.

 

Thank you, however right when you answered I got my answer from OVTune. looks like it: 33

 

Ive yet to see or hear them do it yet. I know there have been requests to them from the NorthStar battery booster thread.

 

Hopefully we find out soon with vf tuner coming out "within" a month. I'll have it when he starts the upgrades.

 

Ok, just ordered one up. May 15th for possible shipping....

 

Mine shipped out quick and is on the way!

 

Just so everyone is aware. I ordered my voltage booster from ebay from Australia with a tentative date of delivery being May 15th. I haven't received any updates so I messaged the seller and he stated that shipping from Australia with the COVID 19 pandemic is taking up to 8 weeks.