MPT 7210a charge from car 12v

2

2weiund2wanzig

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Jun 21, 2020
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Hello,
i am building a portable LiIonbattery for my van (simple diy camping build). I want to build it into a tool box to make it portable.
I already have a MPT 7210a charger that will be inside the toolboxand i would like to be able to charge the battery without solar panelwhile i am driving.
Can i connect (i would use powercon connectors) it to my car battery?

Question: What kind of relay would i need to make sure it only charges when the motor is running to prevent my car starting battery from draining? I think it needs to be something like a voltage meter that opens a relay at the cars charging voltage when the motor is running.
 
1. Your battery need to be atleast 17v or more. The 7210 is boost only.
2. You need any relay but connected to a source where you have Power like the 30+. Aka Power when engine is on. Depends on the car.

Why not just plug it into the cigaretter lighter outlet and instead of that 7210 use a standard Buck/bost converter?
 
Guessing the toolbox battery is >12V. 24V.

Use a 1200W boost converter, set the input voltage limit to say 12.8V. Set output current limit to say 8A. Plug it into the cigaretter lighter outlet as Daroma said.

If you use the 1200W or 1800W units connect the battery pack to the output first as connecting the 12V from the car may in some instances blow the unit. They are great handy units but are designed with solar in mind (constrained input amps).
 
completelycharged said:
Guessing the toolbox battery is >12V. 24V.
Click to expand...

Yes, wanted to build it 24V or 48V

completelycharged said:
Use a 1200W boost converter, set the input voltage limit to say 12.8V. Set output current limit to say 8A. Plug it into the cigaretter lighter outlet as Daroma said.

If you use the 1200W or 1800W units connect the battery pack to the output first as connecting the 12V from the car may in some instances blow the unit. They are great handy units but are designed with solar in mind (constrained input amps).
Click to expand...


Thats cool, i didnt know they have an adjustable input voltage (low voltage protection). Thank you! And also all others for their good hints!
 
The trouble with the cigarette lighter solution is they are limited to 8a - that's only 8 * 12 = 96watts. Even a standard 7-way (trailer connector) will be in 25a max range - e.g. only 300w.

I'm building a cargo trailer -> camper with a 14s/48v 18650 battery bank and have been noodling on how to charge it while driving. I'm hoping for at least 13.5kwh or even 27kwh if I can fit in enough packs... but this requires a 'next level' of charging watts capability beyond a typical RV.

Obviously solar panels are part of this plan - but the other part is charging while driving on a trip. Can I get to 750w/hour charge whiledriving? 750w/12v = 63a sustained.

It seems like abattery isolator (as listed above) is a key piece so you make sure your vehicle battery is charged normally / not affected by secondary charging. Then, how to get 12v to 48v? Maybe a high amp 12v (say 80a = 960watts) 120v inverter -> standard 48v lithium-ion charger(s)?
(Note: I already own 3 x 750w YZPOWER 48v lithium-ion chargers that I run from my generator as emergency power -> battery bank andI was hoping to use 1 or 2 of them in this situation).

Do they make 80-100a 12vDC-48vDC boosters that one can afford? Seems like you would still want the battery isolator as input to the 12vdc -> 48vdc booster or do you need a 12v battery as a buffer?
 
You can most likely not get 63a sustained unless you got a larger gen like an 130-150 or even 200. Note beware that the average modern car easily need 40-80a continues. Like ignition, powersteer IF thats electronic. Ac and fans and so forth.

So before you plan anything before going above 20a you need to crosscheck what the car can handle. The generator on cars are also not made to run 100%
I know thos working with it for a bit :) some rv based cars you can choose different generator versions due to this.

But fr instance My car here with 160a gen they recommend max extra of 30a externaly. Like a caravan or headlights.
 
>But fr instance My car here with 160a gen they recommend max extra of 30a externaly. Like a caravan or headlights.
Yes, appreciate the return to reality. An alternator can *over heat* if used much beyond its design -even if technicallyit can produce amps. They do make higher amp alternators... ones that supposedly will put out 240a (instead of 160a) type of thing...but the reality is that it takes a lot of amps at 12v to get to 1000w range.

Maybe a generator running on the tongueof thetrailer is a better way to think about it.

I'll be interested to see if anyone comments on what they did that was sustainable.
 
People needing of high current /Power for rv or for instance audio tend to add an extra generator instead.

Not doable on all cars though :)

If you have roof space add panels There :)
 
OffGridInTheCity said:
I'm building a cargo trailer -> camper with a 14s/48v 18650 battery bank and have been noodling on how to charge it while driving. I'm hoping for at least 13.5kwh or even 27kwh if I can fit in enough packs... but this requires a 'next level' of charging watts capability beyond a typical RV.
Click to expand...

27kw? Just... why? I run a 400sqm house with 10 people for a 5 days with that haha. Is that still called camping? :) What do you want to run with that?
And... wouldn't it be easier to use solar panels and / or grid power to charge it?
 
2weiund2wanzig said:
OffGridInTheCity said:
I'm building a cargo trailer -> camper with a 14s/48v 18650 battery bank and have been noodling on how to charge it while driving. I'm hoping for at least 13.5kwh or even 27kwh if I can fit in enough packs... but this requires a 'next level' of charging watts capability beyond a typical RV.
Click to expand...

27kw? Just... why? I run a 400sqm house with 10 people for a 5 days with that haha. Is that still called camping? :) What do you want to run with that?
And... wouldn't it be easier to use solar panels and / or grid power to charge it?
Click to expand...

My DIY powerwall batteries are 14s100p'ish - 13.5kwh - each. I've gotten good at building them with 6 in operation(81kwh) and I have enough cells for 2 more (27kwh).

I just got my 7 x 14 cargo trailer - and I think I can put the batteries in the floor (like an EV car). I plan to make the batteries compatible so I can plug the trailer into side of the house when parked and expand my home powerwall. This will make them useful to the house and be 'ready to go' when taking the trailer out - e.g. keep them in regular use and regularly monitored.

I haven't scaled out the system- but I want to plan fora 9000'ish BTUmini-spit cool and heat24hrs/day in moderate climate. Not sure yet what I need - several things to figure outstarting with power needed to run a mini-split 24/7- but with the knowledge I've gained from home powerwall I can figure it. Maybe I'll have to go scale back to 12hrs/day etc - not sure yet but a typical RV setup with a couple of 12v BattleBorn(s)is not nearly enough, will need a level or 2bigger system.

There are 2 base situations - e.g. driving all day / camping at night (less mini-split needed)and boondocking (24/7 minisplit maybe). The driving all day - seems like such a natural thing to want to harness that vehicle engine power for battery chargingsince gas (gas mileage) is not an issue for me. Boondocking all day - then panels take top focus.

The trailer can go up 5,000lbs - so its a matter of space rather than weight I'm pretty sure. Panels on top (maybe 4 x 300w) and perhaps panels stored in the trailer for another 1200w deployed alongside trailer. Ya de ya da.... we'll see :)
 
completelycharged said:
Guessing the toolbox battery is >12V. 24V.

Use a 1200W boost converter, set the input voltage limit to say 12.8V. Set output current limit to say 8A. Plug it into the cigaretter lighter outlet as Daroma said.

If you use the 1200W or 1800W units connect the battery pack to the output first as connecting the 12V from the car may in some instances blow the unit. They are great handy units but are designed with solar in mind (constrained input amps).
Click to expand...


I have one of these:https://www.ebay.de/i/232461793739?chn=ps&norover=1&mkevt=1&mkrid=707-134425-41852-0&mkcid=2&itemid=232461793739&targetid=896427593016&device=c&mktype=pla&googleloc=9068348&poi=&campaignid=10203814986&mkgroupid=101937416117&rlsatarget=pla-896427593016&abcId=1145992&merchantid=138391959&gclid=CjwKCAjw9vn4BRBaEiwAh0muDE0eA84rTtNzPz8H-mFtqsjX0NF35aI4fafK0LP3L4rtkiGINXAY5hoCX5gQAvD_BwE

I am a bit confused by the ratings. When i power it from maybe a 12v server-psu with 2kw and want to charge a battery pack of 24vwith it i can only charge with 12v*20a = 240w and the same as i want to charge a 48v battery because it is the input voltage that matters?
 
2weiund2wanzig said:
I have one of these:https://www.ebay.de/i/232461793739?chn=ps&norover=1&mkevt=1&mkrid=707-134425-41852-0&mkcid=2&itemid=232461793739&targetid=896427593016&device=c&mktype=pla&googleloc=9068348&poi=&campaignid=10203814986&mkgroupid=101937416117&rlsatarget=pla-896427593016&abcId=1145992&merchantid=138391959&gclid=CjwKCAjw9vn4BRBaEiwAh0muDE0eA84rTtNzPz8H-mFtqsjX0NF35aI4fafK0LP3L4rtkiGINXAY5hoCX5gQAvD_BwE

I am a bit confused by the ratings. When i power it from maybe a 12v server-psu with 2kw and want to charge a battery pack of 24vwith it i can only charge with 12v*20a = 240w and the same as i want to charge a 48v battery because it is the input voltage that matters?
Click to expand...
As I read it, it says input current = 20a max. So itlimits input amps regardless of voltage. Which means you're right -12v input @ 20a will limit you to 240w.
The MPT 7210a chargers have a similar concept - they are limited to 10a output regardless of the input power oroutput voltage :)
 
For one of my projects ill need 500w charging minimum. I think i could use 2 of these in parallel. Or is there some other option in that price range?
 
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