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hi matt,

i am interested in other opinions on this as well. as i may adjust my own usage of it.

if the switch is in some position other than the middle "off" position then the two banks of batteries are merged together. to energize the merge solenoid to combine the batteries it doesnt matter if you move the switch in the up or the down position as long as both banks of batteries are charged. that is because all it does is control which bank of batteries provides the power to actually energize the solenoid itself. if both banks of batteries are charged, then either position will merge them. if one set of batteries is not charged, then that bank will not energize the solenoid to merge the batteries to allow you to start the engine associated with that bank of batteries. it does not appear that there is any convention for which position of up or down is connected to switching off of the house or start batteries.

since the batteries are isolated when the switch is off, the only way to charge the main engine starting batteries is to have the engine running.

the other thing is that when the coach engine is running, the system is set up to automatically merge the banks of batteries to charge them while the engine is going.

so to help outline this better. someone jump in if i made a mistake

scenario one. merge switch "off" coach batteries fully charged and starting batteries fully charged. you want to start the coach engine. it should start and turn over just fine. the coach should also have full power to run its systems including the inverter and to start the generator.

scenario two. merge switch "off" coach batteries fully charged and starting batteries low or dead. you want to start the coach engine. it will not turn over or not fast enough to start. now you can move the merge switch either up or down. try up. if then you can start the coach engine easily because you merged the house batteries with the start then up uses the house batteries to power the merge solenoid relay. if up doesnt work, then try down and it should now start. that means that the down position is the one that uses the house batteries to power the relay inside the merge solenoid.

scenario 3. merge sw "off" coach batteries low or dead, engine start batteries fully charged. that means you should not be able to start the generator since it uses the coach batteries. but you should be able to use either up or down on the merge sw to combine the batteries to start the generator. you would want to do this to charge the house batteries to be able to dry camp longer.


i do know that if the coach engine is running, it automatically energizes the merge relay and both banks of batteries are being charged.

what i dont know is if the coach engine is not running and the generator is running does the merge relay automatically energize to do the same thing. i have assumed not and keep the merge switch either up or down.

now as to matts question. which way to keep the switch when the genny is running or the coach is plugged into shore power.

if you are on shore power, the assumption is you are charging the house batteries. if you have the merge switch up or down such that the batteries are merged (if the start batteries are dead, you would need the switch in the position that uses the house batteries to energize the merge relay). or if both banks are fully charged it doesnt matter which position (up or down) is used. then with the coach plugged in, you are keeping both house and starting batteries charged off of the inverter charger.

if you are only on genny power (meaning the genny is charging the house batteries), and you are sitting somewhere with the coach engine off, AND all the batteries are ok, then the merge sw in either position will merge the two banks and the genny will charge all of the batteries.

so....if when on genny power or shore power you keep the merge switch on, you are keeping all the batteries charged off of where the 110v is coming from (genny or power)

that does insure that if the merge relay is working that you will always have all the batteries fully charged when plugged in.

now....newell recommends that the merge relay be changed once a year. this is a continuous duty relay (not like a similar looking starting relay). it is a cole hersee 24106 (or equivalent).

if it is plugged in most of the time, then the relay is energized all the time. that is why i tend to not keep my batteries merged all the time. this is where i could use other opinions.

btw, there is another approach to keeping the starting batteries charged when the merge sw is not up or down. on my 90 i put a "trik l charge" unit on it. it "steals" current from the house batteries to trickle charge the starting batteries and with diodes doesnt allow the house batteries to do the reverse. there is a similar device called an echo charger on my 2002 that i have not yet read enough about to know if it does the same thing or not.

so....if you keep the sw up or down all the time when plugged in or running on genny, then you will keep both banks of batteries charged. if you do this, i would for sure change the merge relay every year to be sure it works. or carry a spare and know how to change it. it isnt very hard.

so, now for the others to comment and correct.

tom