On my ramp truck, I have a separate battery to run my electric winch in the back cubby. I want to charge it from my truck battery while the truck is running. Would I use a SOLENOID RELAY BATTERY ISOLATION SWITCH 12V 300 AMP?
They make battery isolators used in RVs and similar. They charge from alternator, but separate the winch battery from starting battery when engine off.
I have an isolator new in box. Was going to install on pickup camper but traded for motorhome before I got it installed. PM me if interested.
Split the battery feed to the winch across the big terminals, ground one of the small terminals, and power the other small one from an ignition on source.
I've done exactly what you need for my trailer winch battery [the only difference from your scenario is I have an Anderson plug in between at the tow vehicle and trailer.] Just use a 70a relay [they can run continuous duty] But make sure all the wiring can handle the load. These have larger sized spade terminals To limit the current flow [if you're charging a flat battery ] connect in-series an auto reset 40a-50a circuit breaker . If there is too much load the circuit breaker trips, then resets [cycling until the 2 batteries equalize.] The breaker acts like a regulator . The purpose of the relay is for the winch battery not to drain the main vehicle battery [or it won't start] So you want the relay to activate with the engine running [not just ignition switch on] To connect the 2 batteries together , you take a 12v power source from the charge wire on the alternator. This wire goes to the circuit breaker and the from the circuit breaker to the relay [post #30] Post # 30 from Alternator [via circuit breaker] Post # 87 to Winch battery Post # 85 to ground [if the relay is diode protected it must be #85 to ground] Post # 86 splices into the T1 [alt light] wire on the Alternator Post #86 is dead with the ignition on because it takes a path to ground [so #86 AND #85 see ground on both sides] As soon as the engine is running the Alt sends 12v up the Alt light wire and the light sees 12v on both sides [so the light goes out] AND post# 86 now sees 12v [so it closes the relay connecting both batteries together] I did this on my tow vehicle and it set me back $20 [and works automatically without manual switches] Edit: you can buy these 12v to 12v battery chargers for RV's etc but these are limited to 20a [and expensive] The best regulator to use is the one already mounted in the charging system [alternator]
Most likely the solenoid you're using is a non grounded base (the small poles on the front are ground and power to activate the solenoid). If you hook to the ignition wire then the solenoid will close (activate) when running to charge rear battery. But remember if the truck engine is off and ignition is on the batteries will try to equalize (highest voltage will flow to the lowest).
@drumyn29 You don't really want a solenoid connecting 2 batteries together ! You either have them permanently connected [dual batteries] or you need them to be current limited to protect the battery from damage. An 850CCA battery is 65ah A 65ah Lead Acid battery has a maximum charge recommendation of 19.5a A 12000lb winch dragging 12000lb draws about 400a For appox 5 mins total winch time [with cooling cycles between] this = 33ah This would take 102 minutes [1.7 hrs] to recharge at 19.5a [a 40a circuit breaker via a relay would recharge a 50% discharged 800CCA battery in 50 minutes] Here is how I recommended connecting the relay to the battery [using an electric choke diagram as an example] With this ^^^^^ Swap the 20a fuse for a 40a auto reset circuit breaker Swap the choke coil for the battery 12+ Reverse the posts # 85 and #86 if you are using a diode protected relay [otherwise it doesn't really matter] Here is my tow vehicle [apart from an Anderson plug at the hitch, it is reasonably hidden] The yellow arrow is the Auto reset circuit breaker. The red arrow is the 70a relay The blue arrow shows a HD red wire to the trailer battery AND a brown wire that connects to the ALT light wire Top view The yellow arrow is where the Auto reset circuit breaker is The blue arrow is where the factory alternator charge wire connects to the battery, so I connected the circuit breaker to this. You can connect these direct off the back of the Alternator if you want. I only did it this way^^^ because the Alternator was on the L/H Side , But the Battery, Fusebox, Firewall grommets, Instrument cluster , Anderson plug etc is on the R/H side [ being R/H drive]
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