12v Vehicle to 48v Home Battery Bank

[Electric Mistress]

I have a question and I am going to try to keep it very simple. I would like to know the hypothetical outcome as well as any physics behind it.

I was watching Will's latest 48v solar video where he used x4 12v Battle Born Batteries wired in series to create a 48v bank.
I would like to know what would happen if you connected an EV's 12v battery to one of the 12v batteries (parallel) in the battery bank ?

Would this be an effective way of delivering energy from the cars 12v system to the 48volt system ?

Please help me decide if this is a good Idea

 

[Pierre]

You will only be boosting than one battery the EV is connected to and unbalance it from the the other three. As the series current is determined by the weakest battery in the chain you will not gain anything by doing this - just cause problems.

 

[Boondock Saint]

know the hypothetical outcome as well as any physics behind it.

Interesting name. You had me at "simple"

Oh I've seen fire and I've seen rain, I've seen ... wait . . . that's just the fire trucks trying to put out another EV fire burning a hole in the ground.

That's my hypothetical outcome. Might be some physics in there too.


.

 

[Short_Shot]

Without knowing anything about your EV battery or how you plan to connect anything I am going to say that can't be answered and strongly suggest not doing so.

EV batteries are not 12 volts.

 

[Electric Mistress]

You will only be boosting than one battery the EV is connected to and unbalance it from the the other three. As the series current is determined by the weakest battery in the chain you will not gain anything by doing this - just cause problems.

Would the battle born onboard charge management resolve this ?

 

[Electric Mistress]

Without knowing anything about your EV battery or how you plan to connect anything I am going to say that can't be answered and strongly suggest not doing so.

EV batteries are not 12 volts.

Yes but like all cars they have a 12v battery system to power all the accessories , this is charged by a DC to DC converter the same way an alternator works on a old fashioned car.

 

[Short_Shot]

Yes but like all cars they have a 12v battery system to power all the accessories , this is charged by a DC to DC converter the same way an alternator works on a old fashioned car.

Then why bother with the "EV"?

It's just a regular lead car battery in most cases. They're not designed for powering anything for a significant amount of time without being recharged immediately and before significant discharge occurs.

They aren't deep cycle batteries and will be damaged trying to use them this way.

The previous statements about wasting your time putting one in parallel still applies as well.

 

[Short_Shot]

Would the battle born onboard charge management resolve this ?

No

 

[Electric Mistress]

Then why bother with the "EV"?

It's just a regular lead car battery in most cases. They're not designed for powering anything for a significant amount of time without being recharged immediately and before significant discharge occurs.

They aren't deep cycle batteries and will be damaged trying to use them this way.

The previous statements about wasting your time putting one in parallel still applies as well.

The EV's car battery is constantly being charged there would be no deep cycling of the car battery.
Lets just pretend then its old timey car with alternator running if that helps ignore the EV as a factor.

 

[Short_Shot]

The EV's car battery is constantly being charged there would be no deep cycling of the car battery.
Lets just pretend then its old timey car with alternator running if that helps ignore the EV as a factor.

As stated a few times now this would be irrelevant to the system. It wouldn't add anything worth bothering with.

If the EV is constantly recharging this battery then you don't even need the battery in the equation, but that would just cause further issues on its own.

The only way to make this remotely viable would be to run a 12-> 48v DC to DC charger and attach it to the entire pack. You'd also be extremely limited on available current depending on the converter capabilities on the EV. If you have say 60 amps of 12v availability in the car then you'd get <15a of 48v out of it.

The 12V battery would be almost meaningless in this situation other than as a small buffer.

I believe will has a video on using his tesla as a power source but I'm not sure if it's by doing that or something far more complex, since I haven't watched it yet.

 

[Electric Mistress]

As stated a few times now this would be irrelevant to the system. It wouldn't add anything worth bothering with.

If the EV is constantly recharging this battery then you don't even need the battery in the equation, but that would just cause further issues on its own.

The only way to make this remotely viable would be to run a 12-> 48v DC to DC charger and attach it to the entire pack. You'd also be extremely limited on available current depending on the converter capabilities on the EV. If you have say 60 amps of 12v availability in the car then you'd get <15a of 48v out of it.

The 12V battery would be almost meaningless in this situation other than as a small buffer.

I believe will has a video on using his tesla as a power source but I'm not sure if it's by doing that or something far more complex, since I haven't watched it yet.

Ya, Will hooks up his lead acid tesla battery to a 12v dc to ac inverter i think 2kw. This works well.
I have done this and it works very well, the car has 64kw DC battery which is why I am interested in providing even just a kw per hour which is the less than the limit on the EV's DC to DC converter.

I have pulled 150 amps at 12v without issue I believe the DC to DC converter is 2500 watts max I already have this connected to 150 amp fuse.
I am open to another solution for sure. But I am trying to get KWH from the car to the House.

 

[Electric Mistress]

Could I run the car 12v dc into a solar charge controller and connect this to the battery bank ?

 

[Pierre]

SCC will not start. You need at least 18v for it to work but you want to charge a 48v bank ? You will have to start with say 100v input to the SCC to get decent amps at around 54v output. Rather put up some PV panels instead of this DC - DC conversion run-a-round at low efficiency. I also suggest that you watch more videos on these topics.

 

[feo]

As stated, it’s probably best to avoid the battery to battery idea.

The simplest is probably a DC to DC converter from the high voltage pack.
…or the reliable but inefficient 12v->inverter > charger

if I had 64kwh on wheels, I’d sacrifice efficiency for simplicity.

 

[Short_Shot]

As stated, it’s probably best to avoid the battery to battery idea.

The simplest is probably a DC to DC converter from the high voltage pack.
…or the reliable but inefficient 12v->inverter > charger

if I had 64kwh on wheels, I’d sacrifice efficiency for simplicity.

You can go from the 12v battery to 48v and let the vehicle use its own system to provide the 12v.

Don't need to tap into the possibly high voltage pack or use an inefficient AC inverter.

 

[schmism]

You can go from the 12v battery to 48v and let the vehicle use its own system to provide the 12v.

You could, however as Will has previously indicated on the Tesla ( and I assume most other EV) the charging circuit to the 12v battery is limited to like 10-15 amps. So you can pull a woping 180w off the EV. Usefull for charging cell phones and thats about it

 

[Short_Shot]

You could, however as Will has previously indicated on the Tesla ( and I assume most other EV) the charging circuit to the 12v battery is limited to like 10-15 amps. So you can pull a woping 180w off the EV. Usefull for charging cell phones and thats about it

Op indicated 150a was possible with their car but that may very well be just the battery and not the converter output.

 

[noenegdod]

I have a question and I am going to try to keep it very simple. I would like to know the hypothetical outcome as well as any physics behind it.

I was watching Will's latest 48v solar video where he used x4 12v Battle Born Batteries wired in series to create a 48v bank.
I would like to know what would happen if you connected an EV's 12v battery to one of the 12v batteries (parallel) in the battery bank ?

Would this be an effective way of delivering energy from the cars 12v system to the 48volt system ?

Please help me decide if this is a good Idea

If you actually have 150A at 12v available, and dont want to use or cant find a 12-48v converter or dc-dc with the required output, the only way I can think of actually being able to accomplish charging your system is to use relays to switch your 4 batteries from series to parallel making the bank a 12v bank. You can then charge with the vehicle charging system and when done charging switch the bank back to series.

You would have normally closed relays connecting your 4 batteries in series and to the load. Normally open relays connecting your 4 batteries in parallel as well as a normally open relay connecting to the 12v charging system. A switch or ignition signal to energize the relays when the car is started.

This all is probably a bad idea as the batteries could probably over draw the vehicle charging system. When charging you would also not have 48v if that matters.

 

[HRTKD]

I think you guys are missing what the OP is asking about. On my Leaf, there is a 12v accessory battery. It gets charged when the vehicle's main battery is charged from a pedestal or while the car is being driven the 12v battery gets charged using a converter from the main battery to the 12v battery.

What the OP is suggesting is this:

400v+ Main EV Battery -> 12v Accessory Battery -> 12v LiFePO4 battery (just one out of the four)

Yes, that will charge the 12v LiFePO4 battery, but I don't think it's a good idea to do that. On my Leaf, I think the 12v accessory battery is charged periodically when the vehicle has been unused for a while. (Could be wrong on that, it's something I read on the Internet) Consequently, I don't know if the 12v accessory battery would stay charged while you're discharging it. If it does, then it's workable. However, unbalanced charging of one 12v LiFePO4 out of four in a 48v battery bank is a bad idea.

 

[schmism]

Yes, that will charge the 12v LiFePO4 battery, but I don't think it's a good idea to do that. On my Leaf, I think the 12v accessory battery is charged periodically when the vehicle has been unused for a while. (Could be wrong on that, it's something I read on the Internet) Consequently, I don't know if the 12v accessory battery would stay charged while you're discharging it. If it does, then it's workable. However, unbalanced charging of one 12v LiFePO4 out of four in a 48v battery bank is a bad idea.

James May (that James may) had an issue with his Tesla and its 12v accessory battery.

in short trying to do anything significant off the 12v accessory battery on an EV is just a bad idea.