12V Battery needs replacement - Question on power rating of DC/DC (12V) - Refubishment of OBC?

Mitsubishi i-MiEV Forum

Help Support Mitsubishi i-MiEV Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Active member
Jun 29, 2020
Køge/CPH Denmark
Hey thx for having me.
I have already read much about my new old car, which I love. Bought a 2012 EU model with only 26.000km on it.
Have added a diesel burner/heater (Webasto) and are planing to added cruise control and buttons.
I have fixed my AC compressor, which had no rubber dampers left and was "flying" around "below deck".

Enough about what I have been doing to the car.

12V Battery
The 12V battery have been ill treated at the dealership where I bought it. So I have already managed to run it down on me once with a lot of use of the diesel heater (power hungry) on a long trip.
It needs to be replaced. Think I will go with something with more Ah (or Wh). Maybe LiFePO4's or 18650's because I have some in storage.

Power rating on DC/DC converter for 12V
Does anyone know how much power it does supply while charging the battery and running the car?
I am asking, because my radio died on me today (which I saw as a sign of low battery earlier) and I had phone in the AUX for USB charging at max 750mA, while the AC was running on a rather low speed, the radio was on, and full lights (no high beam) were on. All which I think should not run down the 12V battery.
When the radio died (with a large noise and I tried it twice), I then turned the radio, lights and AC off. Had running lights/fog lights on in front.
I charged only 1200mA to the 12V battery when I return home after testing that the car actually produced 14.4V when turned on (READY). Odd I think.
The weather is rather hot (26 degrees C) if that can have anything to do with it.

Would it make any sense to take the OBC apart and refurbish the two snupper caps before they die on me? And is there anything else I could do while inside the OBC?
I am electrical engineer making EVs for airports on a daily basis and good at soldering stuff.

Anything to add? New vacuum pump? Car has never been serviced at the dealer.

Thank you in advance
The DC to DC converter for the 12 volt is rated at 75 amps I believe. It should support any battery you choose to put in there, so long as it's output voltage is a good match for the battery chemistry you choose. I have put AGM batteries spec'ed for early Mazda Miatas in all 3 of my cars and they're still going strong after several years . They are not as tall as the OEM battery, but if you set them on a piece of 2 by 6 cut to fit, they fit in there perfectly, using the OEM hold down hardware

For US cars, the brake vacuum pumps have been changed out under factory recalls, Twice, so we're all on our third pump. I believe the issue was damage from water condensed into the pump, so if yours still has the original 8 year old pump, a pre-emptive change is probably a good idea. Someone with more knowledge of the charger than I would have to advise you on any pre-emptive changes of the parts it contains. I suspect Kiev will chime in here soon and give you some good advice - He knows more about them than anyone here, I suspect

As for the OBC, i think replacing the 20A fuse in the MCU before it blows would be a good idea. If it blows during charging then the blue snubber caps will be damaged or destroyed.

The OBC lid is sealed tightly and can be difficult to remove, but a visual inspection of the snubbers might be useful to determine if the caps were cracked or split, in which case they could be replaced with higher rated devices.