Help replacing an OLD isolator

[tommymsw]

So I am going to assume my isolator is broken (judging by how old it is) and NOT that it was wired wrong. Although it does seem to be wired differently than the instructions I see for new ones.

For example... the alternator goes to the isolator, but the isolator does NOT go to the engine battery. It is as if the alternator itself splits the charge to the engine battery and THEN also to the isolator.

Picture of My isolator

Like A,E,F are all linked together. E comes FROM my alternator and then A just loops up to the isolator (to give it power). C must be wired to my ignition to turn it on and off and I assume the BLACK wire D goes to charge my house battery (It vanishes into the firewall). Although there would then me NO "Negative" running from the isolator to the house battery.

NO LINE goes from the isolator to my engine battery, that battery is connected directly to the alternator.

line F is a mystery... (It is red) and it travels to some kind of thing pictured HERE that seems to be attached to my air conditioning (That is not working AND not even connected anymore)... Not sure if that is relevant.

So TWO questions...

1. How many AMPS do I need the new isolater to be? I saw one on Amazon that was 80 amp and I imagine the one I have is that small at least.

2. Any advice on how to connect the new one? I will just kind of copy the way it is hooked up now (even though it is slightly different than the directions say)

[MrWizard]

IDK
but if the a/c does not work
maybe the previous owner AKA the 'PO' wired it do turn on, using the a/c switch on the dash

try that and see if it comes on and starts charging your battery

[tommymsw]

MrWizard wrote:
sorry there is NO such thing as an air conditioning charger

you may have read some where

about somebody using a 120vac BATTERY charger

many of us carry a battery charger
it serves as a backup, a way to help a neighbor start his car
sometimes an extra boost to what the 'built in' converter is doing

your RV has or should have a 'converter' aka built in battery charger that works automatically when plugged into shore power

Any idea why my isolator is connected FROM the Air Conditioning unit? As well as the alternator?

[MrWizard]

sorry there is NO such thing as an air conditioning charger

you may have read some where

about somebody using a 120vac BATTERY charger

many of us carry a battery charger
it serves as a backup, a way to help a neighbor start his car
sometimes an extra boost to what the 'built in' converter is doing

your RV has or should have a 'converter' aka built in battery charger that works automatically when plugged into shore power

[tommymsw]

Sorry... to the other responder... AC was AIR CONDITIONING. One of the RED wires comes from the AIR CONDITIONING system. I read that the isolators can be charged from alternator, solar, or air conditioning chargers.

Mine appears like it was hooked up to both? Or perhaps to the air conditioning unit and then to the alternator when the air was taken out or broke.

that may also explain why the isolator is connected DIRECTLY to the alternator and NOT through the chassis battery.

I will just replace it with what was there and worry about the rest later. Who knows... maybe replacing will not fix the problem and my problem was in wiring... Although it looks like the wires have been where they are for YEARS.

[MEXICOWANDERER]

I replaced many before my boat repair business was murdered.

Isn't that the truth...

Matt, I have been following your replies for years on this forum. May I state that the boating industry lost a good tech when you were forced to leave.

[Matt_Colie]

What OP has is not an Isolator.
It is a combiner and they are great right up until they go bad. They can be hard to trouble shoot without the main engine running. It can be done. The biggest problem was owner's repairs when they put in a starter contactor and not one rated for continues duty and it burned up every time that they replaced it. They called me for the third or forth. I kept them in stock.

I replaced many before my boat repair business was murdered.

Isolators take more engineering to install and make work few builders want to go to that effort of doing. Some chassis makes don't allow it because of warranty. The isolator in my coach is a designed in double diode. It is 44 years and 170Kmile old like the rest of the coach.

Matt

[j-d]

I looked at Mex's linked relay on Amazon and when I did, noticed there are Three- and Four-Wire versions of these relays.

The one in OP's pic, and the one Chris linked, are Three-wire. Two big lugs for the current that's being switched by the relay, and then one small lug to energize the relay. In this case, from the RUN terminal of the Ignition Switch, or whatever it's linked to. The Relay's CASE must be Grounded to the Vehicle to work. With a Four-Wire, the second small lug goes to Ground also. Could be right to a mounting fastener for the Relay, or off to somewhere else on the vehicle.

[MrWizard]

use a cheap small relay have the contacts stick ! (chassis battery will drain with camper use)

use to small of a diode based isolator and have a diode burn out ! ( battery circuit with bad diode will not charge)

[MrWizard]

tommymsw wrote:
ALSO...

The "extra" red cable to the isolator seems to come from my AC Relay... Why? Was this because it was getting charge power from my AC r AND my alternator? Or to allow the charge from my alternator to go to my AC?

The AC is no longer functioning and disconnected... So I assume I can just tape this wire off and ignore it on the new isolator.

do you mean A/C air-conditioning
or AC like in 120vac

"was getting charge power from my AC" .. what the heck does this mean ?

charge power from your air-conditioning ?

[MEXICOWANDERER]

Yup. I always assume the use is for real. Jumper wires, plumber's tape, and coat hangers allow fun usage without needing to concern ones self with isolators or relays or most everything graded above "basic". I have met innumerable people down here that use a six-inch jumper clip across a failed solenoid and the thought of doing things any other way brings a smile.

[tommymsw]

ALSO...

The "extra" red cable to the isolator seems to come from my AC Relay... Why? Was this because it was getting power from my AC charger AND my alternator? Or to allow the charge from my alternator to go to my AC?

The AC is no longer functioning and disconnected... So I assume I can just tape this wire off and ignore it on the new isolator.

[tommymsw]

Not knowing much about it... I think my BEST bet is to simply replace what is already there, and worry about "upgrading" later.

I am sure like most things, there are people in the RV community that just want to camp and use a LOT of "duct tape and spit", and those that take it REALLY seriously and like to buy nice things and have a spiffy machine...

I have a crappy little '84 and I am not even sure how many times I will take it out this summer. So I am in the "spit and duct tape" category...Although that has not stopped me from spending WAY to much money on Amazon thinking "OOOH!!!! That will be great in my rv!" 🙂

I can see how addictive this new toy may be to me!

[tommymsw]

Well... this does seem to be a highly debatable topic... Here and on other sites I have looked at. Everybody seems to swear by the other thing!

I have been leaning NOW towards maybe a bi-directional SEPARATOR? As it seems this will also allow the engine battery to charge while I am plugged into shore. I do plug into shore at home and may not take the RV out for long time between trips, so this may be a nice feature.

I have NO idea how many amps my alternator is when deciding on the amps for the isolator/separator, but a new alternator for my Chevy G30 says like 68amps... so I am hoping 100amp will do it.

The $15 relay seems enticing as that seems like what is in there now, and again... If it worked for the past 30 years, why change now? I mean if the one in there was working, I would certainly not be changing it.

[Chris_Bryant]

It's actually irrelevant- the wires hooked to the relay are, at best, good for 20-30 amps, when new.

this is the relay- $15.