100 amp alternator through battery isolator issues

[tev123]

Hello.

Bought a 1990 class B a few weeks ago and as you could imagine first order of business was to dismantle all the systems and learn how everything is hooked up and how it works (first rv for me) 🙂

I have an issue and a few questions regarding charging the coach's side battery using the vehicle's alternator:

The camper has 2 batteries, one standard in the engine bay and a deep cycle in the coach to run the appliances, etc. The coach battery gets charged from a battery charger that sits just under the transfer switch/circuit breaker panel. Either the generator or an external 110v line supplies power to it.

The prev. owner had a 100 amp alternator recently installed

There is a battery isolator in the engine bay that is connected a bit suspiciously. Both vehicle battery lead and alternator lead are attached to the same battery post of the isolator. The alternator post has nothing attached. And the aux battery post has a wire that goes through 2 inline 50A circuit breakers to the + post of the circuit breaker panel in the coach's side, where the coach's battery + cable is also connected.


Issues:

I reconnected the alternator lead to the alternator post of the battery isolator. I also noticed that one of the inline circuit breakers was blown, so I bridged it since there was another along the line.

When I turned on the vehicle and checked the readings on the isolator posts, I got 14.4v from the alternator and the aux battery post, but only 12 on the engine battery post. After about 10 seconds the aux battery cable started getting very hot (ie. smoke), so I shut off everything and disconnected the coach battery from the isolator... The wires off the isolator seem to be 8 or 10 gauge. Everything down to the coach's battery + post was warm/hot to the touch.


Questions:

Is it recommended to have the alternator also charge the coach's battery when the engine is running via the isolator? While I travel, it would top off or recharge the coach battery, but I don't know if it is not recommended to charge the deep cycle battery straight out of the alternator (eg. without a sensing battery charger...)

Could the isolator have gone bad? I would have expected the inline circuit breaker to have tripped if > 50A was going through it. Maybe that went bad too? but either way, I would not expect the battery to charge at 50A, right? The isolator is the solid state type and does not look very old; maybe a few years based on corrosion amount compared to other components...

What am I missing?


Thanks!

[MEXICOWANDERER]

LET'S MAKE A DEAL

PM me. Send me your busted 100+ amp isolator and I'll trade you straight across for a general duty transient voltage suppressor that connects inside your rig breaker box. Takes <10 minutes to connect. Color coded black, white ad green wires.

120 amp and larger preferred but the bitsy 70 ampere rated isolators are just too small for my use. The heat sinks are reclaimed and used for Carbon MOSFET heat sinks. Not a green gimmick, carbon MOSFETS actually do something for a living.

CAVEAT: Delayed response my end. It's guaranteed your isolator will sit unmolested in my PO Box maybe for a couple of months, before I can get it. But I'll carry some transient voltage suppressors when I travel north.

Save weight. use a hammer and cold chisel and whack the potting out of the isolator.

[tev123]

Just as a follow up, this is what I did:

- removed the old diode based isolator. it looked swollen as if it had expanded due to overheating

- removed the 2 50A inline circuit breakers; one by the transfer switch and the other one by the isolator in the engine bay. I found out that they had been carbonized internally and were not doing any protection. They were likely shorting against their case and thus why the wire overheated so fast. I could not verify this as removing them destroyed them (they were carbonized and oxidized).

- installed new 50A breakers and an automatic charging relay ( https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A )

- installed a 4 way selector switch ( https://www.bluesea.com/products/6007/m-Series_Mini_Selector_Battery_Switch_-_Red ) so that I can have the batteries charging through either circuit via the automatic relay (mode 1), by-pass the relay altogether and connect both circuits, in case I want to use juice from the chassis battery (mode 2), or disconnect the two circuits (off mode). the 1+2 mode is essentially the same as mode 2.




thanks to everyone for the suggestions

[MEXICOWANDERER]

As a hint no RV OEM has an alternator without remote voltage sensing. Some cruising sailboats connect the alternator direct to the hotel bank and auxillary to the "chassis" motor propulsion system. This is the way I have Quicksilver wired.

[YC_1]

Someone probably changed the alternator and then had to stack the wires onto one post for the internal regulator to function correctly.

I'm concerned about your hot wire issue. If you had a very run down battery the wire could get warm indeed if the full output of the alternator was coursing through the wires.

I really like the suggestion of a mechanical switch. This solves a lot of problems but you have to be diligent and not run the engine battery down accidently. The switch is a very simple and fool proof device. No messing about with solenoids and such.

[wolfe10]

tev123 wrote:
Going to go with the the fully manual option with a 1/2/BOTH/OFF switch

Simpler:

Marine ON-OFF switch.

Alternator B+ and chassis battery to one lug.

House battery to other lug.

That way the chassis battery is always charged when running the engine AND you could not start it with the chassis battery disconnected from alternator (which would blow the alternator diodes).

And to charger both the chassis and house bank, just turn switch ON.

And, if your house bank is fully charged and you will also be in a CG tonight with shore power, leave the switch off. No need to burn extra fuel to over-charge a fully charged battery.

And, it makes are good boost switch.

[landyacht318]

I like the BLueseas Mini 6007m series switch way more than Guest or Perko brands.

http://www.amazon.com/Blue-Sea-Systems-m-Series-Selector/dp/B015ZPJL7M

The Studs on back are still thick with a lot of threads for multiple Lugs, and they are rated at very high continuous amperage and their small size opened up my electrical wall.

I actually use three of these switches. One for switching all stock vehicle loads, one for house loads, and one for the Solar, so that I can easily choose either battery for either duty.

But for the last 4.5 months, I've only had one battery, and all 3 switches are set to 2, which is my Northstar group27 AGM battery, and I've never come close to not being able to start my engine, even when I took 60 of the 90 Available AH from it.

It can pull over 100 amps from my 120 amp alternator when depleted this much, and it appears to love these extreme charging amps. They key is to charge it fully every day and not partial state of charge cycling of it.

Alternator + 200 watts of Solar makes it happy. When I don't drive and can plug in, a Meanwell RSP-500-15 adjustable voltage power supply can dump 40 amps into it and then hold 14.46v for as long as it takes amps to taper to 0.42a.

A fully charged battery is a happy battery.

[tev123]

wolfe10 wrote:
Is this a diode-based battery isolator or solenoid-based battery isolator?

And by putting alternator and both battery wires on the same lug, it is the same as no isolator-- they are all always connected. This is often done when the isolator has failed.

Yes, diode based.
Right, the isolator is basically being bypassed.

Thanks for the response. Going to go with the the fully manual option with a 1/2/BOTH/OFF switch

[tev123]

landyacht318 wrote:
I chose the fully manual option with a 1/2/BOTH/OFF switch

I like the 1/2/both/off manual switch idea. Particularly since the rear battery can get charged from generator or external 110v....

Thanks for the reply

[tev123]

westend wrote:
It sounds like you have eliminated the circuit protection by bypassing the circuit breaker and have the isolator miswired/failed. This, along with a coach battery that is depleted, would be the cause of the heat.

Yes, isolators do go bad. There is also good probability that you will never get 50A from the alternator to the coach battery through a diode isolator when everything is wired correctly.

there were 2 50A circuit breakers in the one line from isolator to rear battery. One was bad (no through current) so I bridged it since the the other one might should have protected. It may be bad as well since it did not trip.

Thanks for the reply

[MEXICOWANDERER]

Finned rectifier isolators, cotton cord tires with tubes and a floorboard starter button work well together. Most finned isolators use rectifiers with 50-volt ratings and reverse leakage through the diodes is atrocious new out of the box and only get worse until they fail. This includes the Sure Power blue anodized brand finned rectifier isolators. They are JUNK!

Using a hugely over-rated isolation relay is a wise alternative. A 200 amp rated isolator working in a 100 amp environment will last 5+ times as long as a 100 amp isolation relay. This is one area I heavily favor the use of automatic switching charge isolators.

[wolfe10]

Is this a diode-based battery isolator or solenoid-based battery isolator?

And by putting alternator and both battery wires on the same lug, it is the same as no isolator-- they are all always connected. This is often done when the isolator has failed.

[westend]

It sounds like you have eliminated the circuit protection by bypassing the circuit breaker and have the isolator miswired/failed. This, along with a coach battery that is depleted, would be the cause of the heat.

Yes, isolators do go bad. There is also good probability that you will never get 50A from the alternator to the coach battery through a diode isolator when everything is wired correctly.

[RoyB]

This is what happens to all trailers after a few years. Many undocumented MODS to deal with...

I would put it back to normal but not remove any of the mod items. I would love to have a second 100AMP ALTERNATOR SETUP in my truck for my additional battery banks if that is what I reading from your comments...

Also you mentioned battery isolator - with todays smart mode charging schemes you cannot use the old DIODE TYPE three port Battery Isolators... The large diodes inside have to much DC VOLTAGE for you to be able to provide the three required charging modes for the additional batteries being 14.4VDC-13.6VDC-13.2VDC.

Todays so-called battery isolators are now accomplished with automatic smart relays that direct connect to the source when needed... Read-up on the BLUE SEA SI-ACR Automatic Charging Relay on-line to see how they provide you charging voltages for additional batteries.
BLUE SEA AUTO CHARGING SMART RELAY SI-ACR

MORE INFO

With the cable getting hot sure sounds like a bad wiring concept or batteries wired in the REVERSE ORDER... I think you found the reason it was disconnected.

I would get it all back to normal and then have the experts tell you what you need to do with what you got...

Just my thoughts - not an expert on any of this...
Roy Ken

[landyacht318]

The diode based isolators are battery killers. Those large finned heat sinks are your hard working alternator amps going up in heat, instead of into the battery. The diode also reduces voltage, basically making it impossible for the battery to ever reach full charge via the alternator, and greatly reducing the amp hours returned into the battery whenever you drive.

Some of the isolators try and trick the alternator into allowing a higher voltage to negate the diode's voltage loss.

You would be better off with a heavy duty continuous duty solenoid rated at 100 amps continuous or higher.

There are voltage sensing solenoids like the surepower 1314 and 1315 or the Blueseas ACR.

I chose the fully manual option with a 1/2/BOTH/OFF switch