dual battery w/isolator and solar charging

[496bb]

So, looking to put in two fresh batteries and make a dual setup. I have a diode isolator. But, I see these Cyrix isolators, and I'm trying to figure out how I could wire in a simple cheap solar trickle charger to keep both batteries topped off, as this won't be a daily driver. Anyone done this?

 

[Ricko1966]

So, looking to put in two fresh batteries and make a dual setup. I have a diode isolator. But, I see these Cyrix isolators, and I'm trying to figure out how I could wire in a simple cheap solar trickle charger to keep both batteries topped off, as this won't be a daily driver. Anyone done this?

Maybe make your life easy. New Volkswagons used to ship with a solar battery maintainer installed,so dealers never had a dead car on the lot. Dealers removed them before sales. They suction cupped to a window and plugged into a cigarette lighter,dealer techs used to peddle them on ebay for 10.00 I bought one there but it's been years. Maybe still a thing,maybe not but easy to check. Just looked on ebay not cheap anymore I snapped you 2 screenshot 1 so you'd have specs.

 

[Grit dog]

^Great piece of trivia or memorabilia but there’s so much out there for solar maintainers compared to whenever VW did that it would imo make sense to use some “new” solar.

So, looking to put in two fresh batteries and make a dual setup. I have a diode isolator. But, I see these Cyrix isolators, and I'm trying to figure out how I could wire in a simple cheap solar trickle charger to keep both batteries topped off, as this won't be a daily driver. Anyone done this?

Considering most of the retailers for the Cyrix also post the installation instructions, I’d just follow those.
If you are installing new, yeah ditch the old diode isolators idea. They still sell em, but why…there has been better technology for quite a while now.
The bigger question is why the isolator? Are you using the batteries as a house/start battery combo or just want the additional battery capacity in general? If the latter then just run batteries in parallel and hook the charger to the most convenient one.
If the former, same thing. Install the isolator/combiner and run the charger to the most convenient one. Same goes for the alternator. Any auto charging relay will work both directions.
I’ve had one on my boat for a lot of years. It’s simple and easy and reliable. (I have a blue sea brand but it’s similar to the Cyrix you posted)

 

[Ricko1966]

^Great piece of trivia or memorabilia but there’s so much out there for solar maintainers compared to whenever VW did that it would imo make sense to use some “new” solar.

Considering most of the retailers for the Cyrix also post the installation instructions, I’d just follow those.
If you are installing new, yeah ditch the old diode isolators idea. They still sell em, but why…there has been better technology for quite a while now.
The bigger question is why the isolator? Are you using the batteries as a house/start battery combo or just want the additional battery capacity in general? If the latter then just run batteries in parallel and hook the charger to the most convenient one.
If the former, same thing. Install the isolator/combiner and run the charger to the most convenient one. Same goes for the alternator. Any auto charging relay will work both directions.
I’ve had one on my boat for a lot of years. It’s simple and easy and reliable. (I have a blue sea brand but it’s similar to the Cyrix you posted)

Has Solar really changed that much since the TDI golfs?

 

[496bb]

Grit,
I looked and I actually have a PAC200 - which actually just connects the two bat + so basically parallel. My concern is that my research indicates this means both batteries will equalize and constantly do so, so they will wear down prematurely.

Old theory is both batteries need to be the same age,CCA, etc - but with the newer Cyrix type intelligent isolators it seems like maybe they can be completely different.

My use would be having the aux batt for camping, off grid power needs, and tailgating type stuff. Current battery is bad so if I need them to be the same, need to buy two now - otherwise I could just do the one and add a second later if the newer isolator technology keeps em separated better.

 

[Ricko1966]

@496bb don't know why this just clicked in my head, you could use a 4 wire trailer plug,two wires connected to 1 battery 2 to the other battery. Another 4 wire connector,2 wires to one solar panel 2 to another. The 4 wire wire plug would keep polarity from being switched 1 plug, plugs in 2 small panels,and charges both batteries independently. Assuming both batteries are isolated when parked.

 

[496bb]

hmmmm, interesting idea

 

[Grit dog]

Has Solar really changed that much since the TDI golfs?

Depends what “that much” means. Efficiency, yeah in the last 30 years, typical efficiency has about doubled and solar panels degrade with time/use as well. So idk where that leaves the 15-25 year old VW units, but that’s not the issue I was referring to. I meant “new” as in not old/used/unknown condition for $50 from some schmuck off of Fleabay.
They were actually decent units at 10W. But again, it’s not like finding a solar charger is difficult or rare. They are more common and numerous now than in the past.

 

[Grit dog]

Grit,
I looked and I actually have a PAC200 - which actually just connects the two bat + so basically parallel. My concern is that my research indicates this means both batteries will equalize and constantly do so, so they will wear down prematurely.

Old theory is both batteries need to be the same age,CCA, etc - but with the newer Cyrix type intelligent isolators it seems like maybe they can be completely different.

My use would be having the aux batt for camping, off grid power needs, and tailgating type stuff. Current battery is bad so if I need them to be the same, need to buy two now - otherwise I could just do the one and add a second later if the newer isolator technology keeps em separated better.

Ok, separating questions here, irrespective of charging/maintaining, regarding combining batteries or isolating them, you want to isolate them as a start battery and house battery.
That’s fine. That pac200 will do that but says it won’t isolate the batteries until 11.6v by its description yet isolates with essentially less than charging voyage by the install document. Guessing a typo and it’s fine for your application because an isolator that waits til a battery is almost dead to unlatch is useless. It is fine for your purposes. I’d use it if that’s what I had in hand. No problem.
Now back to the maintainer question, that depends on frequency of use and parasitic draw from the vehicle, either intended draws or unintended. An old squarebody should have zero intended draws, save for aftermarket components with “memories” like a digital stereo. (Or if you have the last working OE clock in existence, lol!)
So assuming you’re not putting a band-aid on it for unintended parasitic draws, a maintainer is not “really” required unless your letting it sit for idk, pick a number, 6 mo or longer? Typical lead acid batteries lose about 3%/month. A simple knife disconnect on the start battery is cheap and will kill any parasitic draws and your batteries could sit a year or more and still start the truck all things being equal.
I guess if your truck is not parked in the shade and sits out 24-7-365, solar is a good option. With zero parasitic draw, a small 7-10W solar will do the trick. If you’re building this to work around something that’s actively drawing on the the battery(s) then a typical small maintainer like that may not keep them at 100%.
But it’s reasonable to want “topped off” batteries so if your isolator is working and you wire the solar charger to either battery, it should/will trigger the isolator as long as the charger/maintainer puts out over 13.8v (according to PAC). It’s just a bit more clunky and more parts imo than some of the other 1 piece voltage sensing combiners. But you do get a cool little monitor to look at.

 

[Grit dog]

@496bb don't know why this just clicked in my head, you could use a 4 wire trailer plug,two wires connected to 1 battery 2 to the other battery. Another 4 wire connector,2 wires to one solar panel 2 to another. The 4 wire wire plug would keep polarity from being switched 1 plug, plugs in 2 small panels,and charges both batteries independently. Assuming both batteries are isolated when parked.

Electically speaking, that works, whether he has a voltage sensing combiner or a simple solenoid or batteries just hooked in parallel, or batteries completely isolated (not hooked together by any meas). But would only be necesssry if the latter, which is not the case, as there would be no way to charge the second battery without an external charging source.
Maybe I’m missing the advantage of this method in the OPs case or any typical 2 battery setup? Curious as I have/had several different multi battery/bank scenarios in different vehicles/toys over the years.