T-Max dual battery system opinions?

[eddie_yeti]

Just found this thread; I've been using a TMax system for around 8 years now and so far so good. I need to replace my secondary battery, can I use a different battery than my starter battery? Right now they match and I cant find for certain if this system is good with different size/types of batteries.

 

[Herbie]

I used the TMax on my van from ~2010. Was still working well when I sold the van last year, with a couple of caveats:

• As others have noted, the included cables are probably undersized. I ditched these and cut up a pair of 2-gauge jumper cables to build all my wiring.
• The included solenoid failed after about 5-years. I replaced with a 200A continuous duty Cole Hersee solenoid and it has been rock solid ever since
• Yes, the system is "Dual Sensing" - apply a charging voltage to either side of the system and the brain will close the solenoid to connect the batteries. This means the starting battery was conveniently also charged by the rooftop solar and (later) the shore-power charger I added.
• Because the system will just connect the two batteries in parallel for long periods of time (e.g. all the time the engine is running and any time you have any other charger attached), you really want both batteries to have the same voltage profiles, which means you should use the same chemistry. Mixing battery types will mean that one battery would be constantly trying to "charge" the other, which is hard on both of them. In my case, I used a Sears Diehard Platinum (Odyssey AGM) starter battery and a couple of different AGM House batteries. (Diehard Platinum/Odyssey Deep Cycle AGM, and later a Duracell Ultra Platinum (Deka/East Penn) Deep Cycle AGM.)
• For me the system was mostly useful to (a) make sure the starter battery also got charged by solar, etc., and (b) to provide Self-Jump capability. The alternator seldom did a very good job of recharging a depleted house battery because I needed a LOT more current for a lot longer drive than I usually got in a day of touring. The Odyssey Deep Cycle batteries in particular demanded like 45A+ charge currents for multiple hours and I wasn't getting that from the alternator. Good shore-power charger and ample solar solved all my issues, though.

A little more info and some photos here:

Battery Box and Bed Platform

Once again I'm having to play catch-up to get the blog updated with the state of construction on the Astrolander project. These projects st...

herbiesworld.blogspot.com

 

[matoolie]

I’ve been using Tmax for 10+ years on 3 different 4Runners. In all cases I used system with a factory lead acid vehicle battery and an auxiliary AGM battery without any noticeable issues. I’ve transferred the AGM battery between vehicles and on only my second one.

 

[Trail Talk]

I used the TMax on my van from ~2010. Was still working well when I sold the van last year, with a couple of caveats:

• As others have noted, the included cables are probably undersized. I ditched these and cut up a pair of 2-gauge jumper cables to build all my wiring.
• The included solenoid failed after about 5-years. I replaced with a 200A continuous duty Cole Hersee solenoid and it has been rock solid ever since
• Yes, the system is "Dual Sensing" - apply a charging voltage to either side of the system and the brain will close the solenoid to connect the batteries. This means the starting battery was conveniently also charged by the rooftop solar and (later) the shore-power charger I added.
• Because the system will just connect the two batteries in parallel for long periods of time (e.g. all the time the engine is running and any time you have any other charger attached), you really want both batteries to have the same voltage profiles, which means you should use the same chemistry. Mixing battery types will mean that one battery would be constantly trying to "charge" the other, which is hard on both of them. In my case, I used a Sears Diehard Platinum (Odyssey AGM) starter battery and a couple of different AGM House batteries. (Diehard Platinum/Odyssey Deep Cycle AGM, and later a Duracell Ultra Platinum (Deka/East Penn) Deep Cycle AGM.)
• For me the system was mostly useful to (a) make sure the starter battery also got charged by solar, etc., and (b) to provide Self-Jump capability. The alternator seldom did a very good job of recharging a depleted house battery because I needed a LOT more current for a lot longer drive than I usually got in a day of touring. The Odyssey Deep Cycle batteries in particular demanded like 45A+ charge currents for multiple hours and I wasn't getting that from the alternator. Good shore-power charger and ample solar solved all my issues, though.

We had to replace our Samlex dual-sensing relay with an Orion DC to DC charger when upgrading to lithium house batteries due to the incompatible charge profiles, so I’m looking for a replacement solution to charge the FLA truck batteries. Have you heard of anyone documenting installing another Orion DC to DC running the opposite direction?

Another possibility is a dual output inverter, less efficient than a DC to DC but makes sense if we upgrade to the 3000W Multiplus. Sterling has also thrown something into the mix with a brilliant new dual-direction DC to DC!
https://www.12voltplanet.co.uk/sterling-power-bb1240-battery-to-battery-charger-12v12v-40a.html