Hey guys, awhile back i installed a TMAX dual battery kit and a second battery (deep cycle). After about 7 months of use the solenoid actually lit on fire it got so hot.. not sure if it was a wiring error or an internal failure? Anyway i am now finally getting all the wiring redone and installing a new solenoid. What i don't understand is how much and what current runs through the actual solenoid? I have read so many different versions of peoples installs with 80 amp solenoids or even 200 amp solenoids. When the aux battery is dead and the factory one is fully charged the solenoid will switch the alternators current to the aux battery to charge it correct? So does this mean all 85 amps of our alternator are going through the solenoid (since both positive battery wires are connected to it) and into the aux battery? I am trying to figure out what different types of power/current the solenoid sees when in use, thanks for any help!

yeah all the power goes both directions thru that solenoid. when secondary batt is discharged, when vehicle is started and charging is sensed by the solenoid it opens up to allow power thru it from primary to secondary batt. When engine is off, solenoid closed to only allow a discharge from the secondary, if ya wired it right.

Okay so I would need a solenoid that can handle continuous amps and one which has a rating for above the 85 amps our alternator does?

Look at the National Luna kit. It's got a smart control system that might mitigate future disasters.


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You need a "Continuous Duty Solenoid"
http://www.amazon.com/s/ref=nb_sb_ss...id%2Caps%2C215

That little wire that goes to the "Ignition On" wire, i put a toggle switch in there as i don't need to charge that second battery all the time and yes... that solenoid does get hot but catching fire shouldn't have happened if all it's doing is charging a battery and no major draw is going on.

Oops...... Double post

one of those amazon reviews says they are using that solenoid instead of relays..

seems like that's not a good idea

In actuality a continuous duty solenoid is simply a very heavy duty relay. You are using a low current circuit to activate, or trigger, a higher amperage circuit. I have used those continuous duty solenoids with great success since the early 80's. I used them in lieu of isolators that were diode based and prone to failure.

In the modern world we live in isolators have improved, such as the one used in the "Luna" kit mentioned above. I still don't like isolators and prefer solenoids. There are now smart solenoids that will delay the connection until after the voltage in the primary batter stabilizes after starting.

https://www.waytekwire.com/item/7705...iKMaAhwZ8P8HAQ

This one has the ability to be triggered for jump starting yourself. And is rated at 200A. Other brands you could look at are Blue Sea, Intellitec, and True. RedArc as well, but I think they are Australian and hard to get stateside.

Edit: This is another one that I recommended to a friend

http://www.powerstream.com/battery-isolator.htm

Should be able to buy a continuous rated solenoid at any parts supplier. They used them in school buses for years now supplying power to the control panel for lights, heaters, etc

Out of all the smart relays i've investigated the one you recommend is the one i have been waiting to become available..... I have this one on my pickup and it is great .... I will add this one to my 4Runner... If i remember the numbers correctly it kicks on at 12.8 volts when running and when engine is not running kicks off at about the same voltage so that the starting battery is not depleted.
Glad you threw that link in there to remind me

It could be a lot more than 85 amps going through it in that scenario. You're basically doing the same thing that happens when you put a set of jumper cables on to charge a dead battery. The two batteries will try to balance, and the alternator is bringing them both back up.

If you use an isolator it keeps the two batteries separated while still charging both of them, but the downside is you have a small voltage drop across it. The smart isolators mentioned above will bring the dead battery back up to near fully charged, and then bypass the isolation portion with a solenoid. That's the best of both worlds when they work right.

You definitely need a continuous duty solenoid. A standard remote starting solenoid (Ford uses them in trucks for years) are only meant to be on while the starter is turning. (20 seconds or so) The coil that closes the circuit will over heat if left on for long periods of time. Continuous Duty solenoids draw a little more power but will not overheat when activated. They can be left on indefinitely.