very nice write up and a very tidy job!
T-Max Dual Battery Install
- Thread starter KlausVanWinkle
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
thanks, klausVanWinkle for initiating this thread! i'm about to start on the system for my 80! your effort in documenting it is much appreciated!
Thanks very much for this great article. I have just followed it to install my own T-Max system, just as you described. I do however have a problem. The T-Max links and unlinks the battery continuously every 5 seconds or so. I have checked that everything is wired correctly and think that it is caused by one or more of the following: 1. Bad earth - Unlikely as the earths are joined. 2. Bad primary battery - Again unlikely. 3. A threshold problem with the T-Max. Possible, but not way to adjust it to even test that. 4. Bad Design/ Problems with a Land Rover TD5 charging system. The battery voltages change when joined which makes the T-Max unjoin them and then they change so it joins them again. There is no voltage showing for the main battery when unjoined and it shows as 12V when joined. the aux shows as 12.8 when unjoined and the charging voltage is max (14V)
I can't find anyone else with these problems so looking for some advice on what to try next. Anyone?
Thanks.
Steve
I can't find anyone else with these problems so looking for some advice on what to try next. Anyone?
Thanks.
Steve
fireball
SILVER Star
Does this happen when you manually link them? You can do this when the engine is off and that might help troubleshoot.
Manually linking is fine. They link and stay linked until I unlink them. If the engine is running they might stay linked for 5 or 6 seconds then we are back to the way we were before with the linking and unlinking... Very frustrating :-(
fireball
SILVER Star
If there is no voltage showing for the main battery when unjoined then you have wired something incorrectly. You should be able to hit display and it will show the voltage at each battery, unlinked. It sounds like you may have some of the solenoid wiring incorrect?
I have a similar link/unlinking when stopped. It only seem to happen when the fridge is near empty. Have 't paid enough attention to the link/unlink to know if the fridge is running or not during the issue. Fridge is wired to a fuse block from the second battery. Doubt any of this helps you though. The T-Max will display both battery levels when manually linked and unlinked.
Bad controller... Assuming that, in fact you have it wired as designed.
Hmmm. I'll check at the end of the week but it was so simple that if I have managed to wire it wrong then I'm clearly at that stage of life... I hd checked it too. I wonder if the control unit is faulty? I will check the wiring anyway...
gwatts - I see the second battery, just not the primary when I hit display. when linked I see both... RodReb - Will check wiring at the end of the week and report. I agree, bad wiring or faulty controller. shame it took me a year to install it :-(
Thanks everyone for your help. Problem easily solved. Everything was wired correctly (thankfully I'm not that bad) but there was a bad contact at the control box on the red wire. As soon as I fixed that it worked! Now to move on to phase two and start fitting the auxiliary equipment. Onwards and upwards 
I am having an issue with my T-Max dual battery system switching back and forth from linked when charging from a solar panel. I thought I would post it here since similar issues have been discussed and maybe someone can help shed some light on something I might be missing. I'm testing a setup that is installed with a solar panel to charge my dual batteries. It is a 100w panel that is wired through a morning star 10A controller(SS10A) to the axillary battery just as described in the T-max instruction manual in accordance with the SS10A instructions. The T-max instructions state that the controller will automatically link the batteries when charging from a solar source to the AUX battery.
It appears that, when the panel is providing power, the SS10A controller charges the aux battery when the 2 batteries are not linked and the voltage increases to the AUX battery. At the point where the battery voltage is above 14v and increasing several things happen at about the same time. It appears that the Solar controller goes into a float charging mode, and the T-max controller links the batteries. Then the batteries are disconnected within a few(3) seconds. The amount of time it takes to switch back to automatically linked depends on the output from the panel. at 1-6 amps it takes around 4-12 seconds.
This automatic switching back and forth will continue until the solar panel stops producing power or the batteries are manually linked. Of course the controller will automatically disconnect the manual linked operation after 30 minutes and the cycle repeats itself.
My next step is to wire the charging output from the controller to both batteries so they will both charge regardless, But I dont think it should need to be wired that way.
It appears that, when the panel is providing power, the SS10A controller charges the aux battery when the 2 batteries are not linked and the voltage increases to the AUX battery. At the point where the battery voltage is above 14v and increasing several things happen at about the same time. It appears that the Solar controller goes into a float charging mode, and the T-max controller links the batteries. Then the batteries are disconnected within a few(3) seconds. The amount of time it takes to switch back to automatically linked depends on the output from the panel. at 1-6 amps it takes around 4-12 seconds.
This automatic switching back and forth will continue until the solar panel stops producing power or the batteries are manually linked. Of course the controller will automatically disconnect the manual linked operation after 30 minutes and the cycle repeats itself.
My next step is to wire the charging output from the controller to both batteries so they will both charge regardless, But I dont think it should need to be wired that way.
I am going to answer my own question to this issue in case others encounter it and offer a bit of info and a solution to the matter.
It seems that the issue that I was having and described above, is related to the sensitivity of the T-Max cut out voltage for charging and connecting/disconnecting the batteries.
I Found that at ~13.3 volts the T-max controller will connect both batteries for charging. The owners instructions provide this cut in spec, but do not provide the cut out/off spec. In any case, it is relatively easy for my auxiliary battery to reach that 13.3 volts with minimal charge from the solar controller. Then the T-max controller activates the solenoid and links both batteries. At this time the voltage drops. This is based on the state of charge of the main battery and the voltage drop across the solenoid or other loads. My voltage would often drop to 12.8 volts. This is low enough for the T-max controller to disconnect the batteries. Within 30 seconds of being disconnected, the charging voltage of the auxiliary battery reaches above 13.3 volts and this cycle repeats itself.
The sensitivity of the cut in cut out settings on the T-max controller operated the battery solenoid much more often than I desire.
I also did not like that the T-max controller automatically links both batteries when the vehicle is started. The National Luna controller has a timer that requires a 5 minute run time before connecting the batteries, and this helps ensure that the main battery is charged(and also reduces the load on the alternator) before connecting both batteries. I do prefer the T-max controller monitor to the National Luna design(this is just a personal preference of having the 90sec timer for the status display and not having a separate intelligent solenoid controller).
I decided to add an on- off -on switch to the green lead from the controller that operates the battery link solenoid. This gives me 3 main options.
1- ON-(green to ground) both batteries linked all of the time allows jump starting and charging and avoids any timers to automatically disconnect the batteries.
2- OFF- keeps both batteries disconnected all of the time. (this is the one that I am using most often) In a standard single battery setup the main battery does not need additional charging from sources other than the alternator during normal operation most of the time. This prevents my main battery from being discharged by auxiliary loads. My Solar panel is an adequate charging source to keep my auxiliary battery charged most of the time, depending on the sun and loads. I can always connect both batteries during a long drive, if my auxiliary battery needs charging.
3- ON- (green to green) resumes operation as designed by the T-max controller.
Here is a picture of my switch under the T-max controller. easy to access yet out of the way. My T-Max controller is installed to a hinge with a magnet to hold it shut.
It seems that the issue that I was having and described above, is related to the sensitivity of the T-Max cut out voltage for charging and connecting/disconnecting the batteries.
I Found that at ~13.3 volts the T-max controller will connect both batteries for charging. The owners instructions provide this cut in spec, but do not provide the cut out/off spec. In any case, it is relatively easy for my auxiliary battery to reach that 13.3 volts with minimal charge from the solar controller. Then the T-max controller activates the solenoid and links both batteries. At this time the voltage drops. This is based on the state of charge of the main battery and the voltage drop across the solenoid or other loads. My voltage would often drop to 12.8 volts. This is low enough for the T-max controller to disconnect the batteries. Within 30 seconds of being disconnected, the charging voltage of the auxiliary battery reaches above 13.3 volts and this cycle repeats itself.
The sensitivity of the cut in cut out settings on the T-max controller operated the battery solenoid much more often than I desire.
I also did not like that the T-max controller automatically links both batteries when the vehicle is started. The National Luna controller has a timer that requires a 5 minute run time before connecting the batteries, and this helps ensure that the main battery is charged(and also reduces the load on the alternator) before connecting both batteries. I do prefer the T-max controller monitor to the National Luna design(this is just a personal preference of having the 90sec timer for the status display and not having a separate intelligent solenoid controller).
I decided to add an on- off -on switch to the green lead from the controller that operates the battery link solenoid. This gives me 3 main options.
1- ON-(green to ground) both batteries linked all of the time allows jump starting and charging and avoids any timers to automatically disconnect the batteries.
2- OFF- keeps both batteries disconnected all of the time. (this is the one that I am using most often) In a standard single battery setup the main battery does not need additional charging from sources other than the alternator during normal operation most of the time. This prevents my main battery from being discharged by auxiliary loads. My Solar panel is an adequate charging source to keep my auxiliary battery charged most of the time, depending on the sun and loads. I can always connect both batteries during a long drive, if my auxiliary battery needs charging.
3- ON- (green to green) resumes operation as designed by the T-max controller.
Here is a picture of my switch under the T-max controller. easy to access yet out of the way. My T-Max controller is installed to a hinge with a magnet to hold it shut.
screendoor
SILVER Star
I've implemented a similar solutiion since I ran into the same issue when charging with solar. My switch is under the hood and does the same thing. Anyone planning on using T-Max with solar will need to do this mod. For solar, check out this as a replacement for T-Max
CTEK (56-677) D250S 5-Step, Automatic DUAL 12 Volt 20 Amp Battery Charger https://www.amazon.com/dp/B005LBCVL4/ref=cm_sw_r_cp_api_X2xayb1CRQZRT
CTEK (56-677) D250S 5-Step, Automatic DUAL 12 Volt 20 Amp Battery Charger https://www.amazon.com/dp/B005LBCVL4/ref=cm_sw_r_cp_api_X2xayb1CRQZRT
fireball
SILVER Star
This is a great thread and thanks to Klaus for doing the original write up. I used this as a resource for my own setup.
That said, if I had to do it all over again, I'd definitely skip the 2nd battery. I'd go with a large Group 31 main battery and a 100W solo panel on the roof rack. The dual battery system adds a level of cost, weight and complexity that IMO is only needed if you do the type of camping where you are parked solo for days at a time.
I'd encourage folks to seriously consider their needs, and the type of travel/adventure/camping/trips that they do before jumping into a 2nd battery install. At the least, search for some of the threads where folks have "swapped" the batteries, using the aux battery location as the main starter, and using the group 31 OEM location as the house battery. That makes good sense with the 2x larger battery powering the house loads/fridge/etc.
My $.02
That said, if I had to do it all over again, I'd definitely skip the 2nd battery. I'd go with a large Group 31 main battery and a 100W solo panel on the roof rack. The dual battery system adds a level of cost, weight and complexity that IMO is only needed if you do the type of camping where you are parked solo for days at a time.
I'd encourage folks to seriously consider their needs, and the type of travel/adventure/camping/trips that they do before jumping into a 2nd battery install. At the least, search for some of the threads where folks have "swapped" the batteries, using the aux battery location as the main starter, and using the group 31 OEM location as the house battery. That makes good sense with the 2x larger battery powering the house loads/fridge/etc.
My $.02
Just came to add another successful install thanks to the beautiful write-up by @KlausVanWinkle. Thank you sir!
