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DC-DC Converter always on

Posted: Mon Sep 14, 2020 7:50 am
by yannd
Hi, I'm looking for a simple way to keep the DC-DC Converter always on to keep a secondary 12V Battery Bank always charged (I already have a DC-DC 12V 20A Charger installed) I don't want to drain the 12V onboard battery and for now the only way to keep the converter ON is on Ready Mode or while charging, but I want it to stay ON as well when simply parked (without the Ready Mode draining extra power)

Any clues on how to do it ? Can I "cheat" the charging mode so the car thinks it's plugged in or is the only way to physically modify the DC-DC converter ? I already have a Canbus Telematics box connected, maybe by modifying some CAN signals ?

Basically, the goal is to use the 400V pack as a an extra stationary battery bank for my 12V Inverter solar charging system (which already has 4kWh). I know the max transfer power will be around 600-800W, which is enough to keep the 4kWh topped when needed.

Any ideas are welcome,

Thanks,

Re: DC-DC Converter always on

Posted: Tue Sep 15, 2020 2:43 pm
by veimi
yannd wrote: I don't want to drain the 12V onboard battery and for now the only way to keep the converter ON is on Ready Mode or while charging,

I was interested in your comment that the 12V battery is being charged when the main battery is being charged,

A few years ago my car wouldn't start because of a discharged 12V battery. If my memory serves me correctly, charging the car did not fix the problem.

I was wondering how you determined that the 12V battery is being charged when the main battery is being charged.

Re: DC-DC Converter always on

Posted: Tue Sep 15, 2020 4:36 pm
by PV1
Watch the dome lights when you plug the car in. After a couple seconds, you should see them get slightly brighter.

As for the original question, due to the car’s design, I doubt there would be much energy savings if you can get just the DC-DC powered up without full READY.

Re: DC-DC Converter always on

Posted: Wed Sep 16, 2020 7:50 am
by Don
veimi wrote:I was wondering how you determined that the 12V battery is being charged when the main battery is being charged.


Because page 1-17 of the owners manual says so -
NOTE
● The 12V starter battery will be automatically charged during charging and also while the ready indicator is illuminated. Refer
to “Ready indicator” on page 3-72.

Don

Re: DC-DC Converter always on

Posted: Wed Sep 16, 2020 1:45 pm
by yannd
As for the original question, due to the car’s design, I doubt there would be much energy savings if you can get just the DC-DC powered up without full READY.
The goal is for the secondary 12v battery bank to always charge when I'm not driving or charging it.

Re: DC-DC Converter always on

Posted: Wed Sep 16, 2020 5:19 pm
by kiev
Does your car have DCQC Chademo port? If so then you could access the 360V pack thru that port and use it with a DCDC converter to create a 12V supply for charging a secondary 12V bank.

i explained how to do this in a post about the Chademo port with pictures and description of how to "open" the port to expose HV on the terminals.

Re: DC-DC Converter always on

Posted: Thu Sep 17, 2020 5:43 am
by veimi
Don wrote:
veimi wrote:I was wondering how you determined that the 12V battery is being charged when the main battery is being charged.


Because page 1-17 of the owners manual says so -
NOTE
● The 12V starter battery will be automatically charged during charging and also while the ready indicator is illuminated. Refer
to “Ready indicator” on page 3-72.

Don

After some time of non use, my 12V battery recently died and the car wouldn"t start. I charged it with a battery charger.

I'm fairly certain that recharging the car that had a dead 12V battery did not recharge my discharged 12V battery on a previous occasion.

It's something I will have to retest should it ever happen again.

Others on this forum have also had their cars not start because of a bad or discharged 12V battery and to my knowledge there has never been any report of success or a suggestion to fix the problem by simply charging the car.

Re: DC-DC Converter always on

Posted: Thu Sep 17, 2020 6:02 am
by yannd
veimi wrote:
Don wrote:
veimi wrote:I was wondering how you determined that the 12V battery is being charged when the main battery is being charged.


Because page 1-17 of the owners manual says so -
NOTE
● The 12V starter battery will be automatically charged during charging and also while the ready indicator is illuminated. Refer
to “Ready indicator” on page 3-72.

Don

After some time of non use, my 12V battery recently died and i charged it with a battery charger.

I'm fairly certain that recharging the car that had a dead 12V battery did not recharge my discharged 12V battery on a previous occasion.

It's something I will have to retest should it ever happen again.

Others on this forum have also had their cars not start because of a bad 12V battery and to my knowledge there has never been any report of success or a suggestion to fix the problem by simply charging the car.


The charging will work only if the 12v battery is still around 11v. Below that it won't be able to start the 400v dc-dc contactor or charging process. So it works to keep the 12v charged, but not to "repair" a dead 12v battery.

Re: DC-DC Converter always on

Posted: Thu Sep 17, 2020 6:07 am
by kiev
A weak, old or worn out 12V aux can be so degraded that it no longer charges anymore by any method, either by the car when charging the HV, or externally using a lead battery charger. When unloaded it may even read 12V with a DMM, but that is a false artifact.

A good strong 12V aux is needed in order to charge the pack because of all the ECUs, relays and contactors that must first be actuated by the 12V aux before the HV charging session will begin. Maybe a weak aux will have just enough juice left to get the session started, but it is so degraded itself that it doesn't accept any significant charge from the DCDC during the session.

We have seen this many times--the pages of this forum contain numerous accounts of issues due to a weak, old or worn out 12V Auxillary Battery.

Cheers,

Re: DC-DC Converter always on

Posted: Thu Sep 17, 2020 6:23 am
by veimi
Don wrote:
veimi wrote:I was wondering how you determined that the 12V battery is being charged when the main battery is being charged.


Because page 1-17 of the owners manual says so -

yannd wrote:The charging will work only if the 12v battery is still around 11v. Below that it won't be able to start the 400v dc-dc contactor or charging process. So it works to keep the 12v charged, but not to "repair" a dead 12v battery.

Thank you!

I feel better that it wasn't just my imagination now that it has been confirmed that charging the car does not always recharge the 12V battery.