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Old 07-17-2022, 06:17 PM   #1
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DC to DC charger: isolated or not? wattage?

New batteries in the van (1994 Ford EB with 7.5L V8) leads me to look to upgrade my charging system to take better care of them. Went from FLA to AGM and my old MPPT charge controller was not configurable, so I've upgraded that to a Victron MPPT that I can set my bulk and float explicitly on.

Next step is DC to DC charger, 3 stage programmable to better take care of the batteries on long drives. I've liked Victron a lot (off grid cabin, boat) so most likely going to stick with that brand:
https://www.victronenergy.com/dc-dc-converters

My two big questions are:
1) Isolated or non-isolated? I can't necessarily wrap my brain around what the isolated gets me over the non-isolated. I can see that the install of the non-insolated would probably be a lot easier (I have a nice big positive feed already wired to under the gaucho to charge the house batteries, but no corresponding nice fat ground wire, would have to run that back to the engine compartment if I went isolated).
2) Sizing? I don't want to fry my alternator with too much demand. I don't know what alternator is in there, I believe it's the high output so 130A instead of the standard 95A. Would a 30A charger like this:
https://www.amazon.com/Victron-Energ.../dp/B086Q8YNJZ
... be too much if the batteries are quite depleted? Not lithium so shouldn't be sucking huge power but would I be safer with 15A?
https://www.amazon.com/Victron-Orion.../dp/B086KWWK44
Would be sort of a bummer to pay same amount for half the output, but the whole point is to not cook anything (batteries, alternators etc), and from my reading you can't derate the 30A to put out less power you have to buy a 15A if you want less watts out.

Thanks in advance,

-- Bass
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Old 07-17-2022, 07:24 PM   #2
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Being that you most likely have a common ground between the house and van battery systems, there is no inherent need for an isolated system unless you are installing shunts to monitor current flow on input and output.

As far as sizing, I believe you would be compromised with the smaller alternator going with 30. In that happens I would look at a larger alt.

Or purchase a unit that can be derated.


greg
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Old 07-19-2022, 12:18 PM   #3
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I have this for sale, new never used $165

https://www.amazon.com/Victron-Energ.../dp/B086Q8YNJZ
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Old 07-21-2022, 06:35 AM   #4
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Quote:
Originally Posted by bob949 View Post
I have this for sale, new never used $165

https://www.amazon.com/Victron-Energ.../dp/B086Q8YNJZ

Thanks, wish I could take you up on the offer but I think I'm going to have to go 15A, the 30A is going to be too much for my alternator based on some reading. Renogy says use a 20A or smaller if your alternator is 160 or smaller... I can't find any markings on my alternator but it's stock not aftermarket so biggest it could be is 130 (I'm assuming Sportsmobile spec'ed these with the larger alternator option when they bought the vans).


Just curious, why did you not install it?


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Old 07-21-2022, 08:50 AM   #5
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I did not install due to selling that project van and moving on to something else.

Good luck with your install!
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Old 07-21-2022, 10:59 AM   #6
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I know you said you prefer Victron, but I have a (used) Kisae DMT1230 for sale if you're interested. It can be set at 5/10/20/30A max charging rate.

https://www.kisaepower.com/products/dmt1230/

It worked great, but I replaced it with a Kisae DMT1250 for both higher charge rate (50A, might as well since I have a LiFePO4 system) and remote control/display compatibility (I'm told the remote doesn't work with the DMT1230).
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