We have a 19 foot Hybrid. We will not do a lot of boondocking. i have a 100 amp Gel cell and a gel cell charger that keeps it properly topped off. Meanwhile, the campers 12V power supply would damage the gell. So i want to isolate the gel from the campers 12 volt system when I have shore power. One option would be a 110V relay that cut out the gel whenever 110VAC is present A cheaper simpler option would be a diode to prevent the camper power supply from putting voltage to the battery. But i wonder the battery would charge properly if it also had communication with the rest of the DC system?Is there an existing product in the RV tool box? thanks

I would disconnect the converter and just power the gel charger. You shouldn't have to have a converter running for 12v.

2oldman wrote:I would disconnect the converter and just power the gel charger. You shouldn't have to have a converter running for 12v.Everything in the camper is 12V, lights, water pump, furnace, control board for the fridge, etc. So the gell would be going through many unnecessary discharge cycles as the small charger tries to keep up. Rather, i want the buzz box to provide all that DC power as we use campground power for the Air Conditioner and the fridge. But for the drive to the destination, which might take two days, i want the gel to keep everything humming. It's perfect for the duty cycle i have in mind, i just to automate the charging and keep the house power supply from cooking my expensive battery.

hertfordnc wrote:So the gell would be going through many unnecessary discharge cycles as the small charger tries to keep up. How small? You only want this expensive battery for on the road? I'm sorry but this is a bit strange.

2oldman wrote:hertfordnc wrote:So the gell would be going through many unnecessary discharge cycles as the small charger tries to keep up. How small? You only want this expensive battery for on the road? I'm sorry but this is a bit strange.First, I am a bit strange. Second, i already have the gell and the charger and the camper needs a new battery so the cheapest solution is to just figure out how to isolate it.

hertfordnc wrote:2oldman wrote:hertfordnc wrote:So the gell would be going through many unnecessary discharge cycles as the small charger tries to keep up. How small? You only want this expensive battery for on the road? I'm sorry but this is a bit strange.First, I am a bit strange. Second, i already have the gell and the charger and the camper needs a new battery so the cheapest solution is to just figure out how to isolate it.Sell the gel cell on Ebay or CL, then buy the appropriate smallest RV/ MarineFLA.. I see absolutely no advantage or reason to hold on to the gel battery because you will need to make unnecessary alterations to make it "work" introducing potential points of failure.New 100 Ahr gel batteries seem to be going for $189-$240, a used good one surely you could get $100 for it which is more than what it would cost for a new group 24 FLA battery..

Cheap way to isolate and charge gel cell- relay or diode ?

hertfordnc
Explorer
Apr 21, 2020
Actually a relay is about $20 and a diode might be 10 or $12.
Wiring it up is easy.
And somewhere in there is the answer to my question I was just hoping somebody with electrical knowledge would connect the dots.

My recollection when I joined this Forum 16 years ago was it there was a great deal of discussion about ways to improve on a manufactured product, cams, headers, axle swaps, I could barely keep up.

I think the culture here has been influenced by social media.
But when I do work this out I'll let you know how it went
Lwiddis
Explorer II
Apr 21, 2020
If you want a project, proceed! If you want to go camping, dump the gel, replace with a wet cell and go camping.
wolfe10
Explorer
Apr 21, 2020
Dave,

Can you give us the FACTS I asked for just above your last post. That will take the BS out of answers.

Hopefully, you want to base your decisions on FACTS, not options.
hertfordnc
Explorer
Apr 21, 2020
wolfe10 wrote:

Gel batteries are OK at a HIGHER voltage than wet cells. So, unless you are really over-charging the other bank (wet-cell or AGM), I don't see the issue.

Perhaps i'm missing something, it is my understanding that gels need to be smart-charged with a higher initial voltage of 14.5 or so falling to something lower at 80%

My power supply is a 40 amp WFCO converter which i believe will not be appropriate for the gels.

Meanwhile, i have a small smart charger that automatically switches to float after a certain charge lever.

Also, because i happen to have the gels i plan to put one of both in a void inside where they can be unvented. That takes 100 lb off the tongue and leaves the front battery box handy for tools or rags or beer.
RLS7201
Explorer II
Apr 21, 2020
Diodes will have at least 0.6 voltage drop. Not a good idea.
If you continue with you plan, use a isolator relay.

Richard
boogie_4wheel
Explorer
Apr 22, 2020
You'll need an interposing relay that has a 120VAC coil, and a normally closed (N.C.) contact. The relay needs to be rated for the max amperage that you plan on drawing from the battery.

Stick the relay inline between the battery connection on the converter and the battery itself. Wire the coil of the relay to any one of the circuit breakers on the converter.

When plugged in to shore power, the relay will be energized, opening the contact and isolating the battery. The converter's DC output will power the trailer. Your gel charger would now be charging the battery.

When unplugged from shore power, the de-energized relay contact would be closed and the battery would now be powering the lights/fridge/water...
hertfordnc
Explorer
Apr 22, 2020
boogie_4wheel wrote:
You'll need an interposing relay that has a 120VAC coil, and a normally closed (N.C.) contact. The relay needs to be rated for the max amperage that you plan on drawing from the battery. \

THank you. That word "interposing" was a game changer in finding the right gizmo.
MrWizard
Moderator
Apr 22, 2020
1972 Revcon
Old Magtek converter
A diode is not going to do what you want
Either get a different battery
Or
Install a different converter
Even then you have to deal with the alternator voltage ,
Unless you disconnect the house from the alternator/isolator/combiner
And have no charging to the gel battery while engine is running

Are you sure it says GEL on the battery
And not Sealed AGM ?
Many people come on here calling any sealed battery Gel

AGM does not require any special treatment, other than a slightly higher max charging voltage,
Much better suited to RV use than Gel
beemerphile1
Explorer
Apr 22, 2020
I used to have slightly used gel cell batteries because I got Deka group 24 gel cells for free. I always let the converter take care of them without trouble.
wa8yxm
Explorer III
Apr 22, 2020
wolfe10 wrote:
Perhaps I do NOT understand the question.

Gel batteries are OK at a HIGHER voltage than wet cells. So, unless you are really over-charging the other bank (wet-cell or AGM), I don't see the issue.

There is a whole lot of confusion over Gel Cells. a lot of it thanks to OPTIMA who advertises their AGM batteries as GEL

AGM's are very very forgiving and take a slightly higher charge voltage from what I understand. Some of 'em can take a seriously faster charger (oters not recommended)

Gel on the other hand is a very very very picky eater. Charge 'em too fast or too high a voltage and they won't make you happy.

I know the O/P said "Gel" but gel's in the sizes we use.. not popular.