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I want to isolate my 32Amp RV Converter / Charger from the battery system. I’m pulling the charger circuit from the converter but I’m still not convinced my ‘expensive’ battery bank is safe.
I want to put a diode in the line from my 12VDC battery bank to the converter’s 12V fuse panel to prevent any kind of trouble / feedback to my Li-Ion batteries when the converter is on 120VAC and providing 12vdc to the fuse panel.
I’m trying to find a Thru Hole 30 Amp / 12VDC or 15VDC diode in the DigiKey listings and I’m not having any luck? Can someone give me a link?
Option??
A little more expensive, but, would it be better to install a relay (with integrated protection) that auto-disconnects the battery bank when the converter is plugged into 120VAC and then reconnects when 120VAC is pulled?
First you’ll want a diode with a lot more maximum current than 30A for a 32A system, I’d typically use a 60A or higher diode. Second you want a reverse voltage a lot higher then the 14 to 15V maximum the circuit can have, I’d pick 30V.
Here’s a search for in stock, 60A and greater diodes, all of them have a 40V or higher maximum reverse voltage rating. https://www.digikey.com/short/zw3wv2
Do be aware that the diode will drop 0.5 to 1.1V depending on the current. You will also need to handle the heat generated when 30W (30A @ 1V) is dissipated in the diode.
A relay will have a much smaller voltage drop and very little heat generation. Here’s a selection of automotive grade relays that should work. https://www.digikey.com/short/zw3nqm
This relay in particular should be easy to use since it has a mounting tab for bolting to the RV and has standard spade lug terminals commonly used in automotive connections. https://www.digikey.com/short/zw3njt
Good advice, @PaulHutch, regarding the diode. I would err on the high side of the voltage - like 60V or more, just to add additional margin. Of your list, that chassis-mount T70HFL20S02-ND seems an especially good choice, as it makes installation easier. It does need a heat sink, but the metal surface on this particular one makes that easier to accomplish than most.
Regarding the relay option, I believe you would need either a normally closed single pole single throw (SPST-NC) or a single pole double throw (SPDT), which has a normally open and normally closed contact, to open your DC battery circuit.
I did an extensive search and could not come up with any relays in stock which had an AC coil and which could open a 30A+ DC circuit in either SPST or SPDT. I did find some 12V DC coil relays which could do so, including the 2449-A3M1CSQ12VDC2-ND.
Keep in mind that these require a 12V DC signal to actuate the switch, so you must be able to provide that when you plug 120VAC into your converter. That may take a little jury rigging to accomplish.
Looked at the relay. Another good choice. Like the higher values.
I’ll have to do a little ‘relay’ research for the wiring. Basically I want the converter to do the coil enegize to disconnect the battery circuit, and release / connect the circuit when the converter is unpluged.
Don’t want the battery circuit powering the relay.
If you have 12V DC from your converter, you should be good, as long as it can provide sufficient current to power the coil. The coil of the 2449-A3M1CSQ12VDC2-ND requires about 150mA at 12V DC, so be sure the converter can provide that much current. To disconnect your DC load from your battery, be sure to connect it to the normally-closed contact, so that it opens when the relay is energized.
This is a great thread. I am facing a similar challenge.
I am not an electrician, so I have a couple of questions in regard to “pulling the charger circuit from the converter” .
Do you physically remove the circuit? or do you pull the converter fuse? That would cut out the 12V system in the trailer.
I am running 200AH LiFePO4 batteries on a 600W solar system through a 2000W inverter as shore power for campgrounds without 120V shore power supply. My idea is to simply plug the trailer shore power cable into the inverter during those times.
My question is, how do I isolate the charge circuit from the converter back to the batteries? I don’t want to use the inverter to charge the batteries it is pulling power from, but I also want the trailer to have normal 12V battery power to the lights, furnace etc wthout the inverter running.
Any help would be much appreciated.
The original poster’s specific plans/intentions with regard to “pulling the charger circuit…” are unclear, and in any case the specifics would seem likely to vary depending on the exact equipment in question.
In regard to your question, it would seem plausible that installing a normally-closed relay (or using the NC contacts of a double-throw relay) between the battery and the 12V system connection could be a solution. If this relay is energized when the AC network in the trailer has power, it would disconnect the battery and prevent the on-board AC-DC charger from engaging in conflict with one’s solar charge apparatus.
The 2449-A3M1CSQ12VDC2-ND relay mentioned previously (or one like it) may be an option (particularly for smaller installations with minimal loads) but I’d suggest that something more beefy such as a 9-1415001-5 might be a preferable option. It’s a 12V relay, so some sort of AC-DC converter would be needed to power it when the AC network is live; while a common “wall wart” could certainly work, something that could be hard wired may be preferable. Under this concept, you’d plug your shore power cable into the inverter when operating it, obviating any need to install any sort of shore/inverter transfer switch. It’s sub-optimal from the standpoint that 12V loads would be supplied via a double-conversion on battery power and thus consume more than they would otherwise, and that battery charging from shore power is not available. It seems however, the least complex path toward your stated goal.
