Solar 12v Battery Charging

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jaraczs

Well-known member
Joined
Aug 6, 2012
Messages
114
Location
Somerset, NJ
PV1 said:
Combine that with a solar panel somewhere on the car, and you shouldn't have to worry about the 12 volt system going dead again. :cool:
And that is exactly the idea I am thinking of. Based on some estimate I made, if I cover the dash under the windshield with ~30 carefully arranged 3x6" solar cells (1.9W at 0.5V each) and sneak MTTP somewhere, I should be able to have 57Watt system when sun is shining. This would perhaps require to disconnect the charging via DC-DC inverter and for the sake of safety, have Voltmeter gauge on the dash and relay switch in place to engage it back in case of lack of sun shine.
I was playing with the DC-DC charger and when disconnected, the car was working with red battery light and some other orange error light on.
Do we have another thread with this topic or shall we continue here?
 
The only thread that comes to mind is the range-extender thread, but that deals with the high voltage system or pusher trailers.

How did you disconnect the DC-DC converter? The other light was probably the EV warning light, a car with an exclamation point on top of it.

A simple blocking diode between the 12 volt system and the converter should stop voltage backfeed to the converter, but who knows if the converter either already has it or needs to see 12 volts to function.
 
Um, exactly what problem are we trying to solve?

For everyday use I really have to wonder about it's need - unlike jaraczs' very useful heater modification.

As soon as the existing dc-dc is energized, it "fills" the (already almost full) 12v battery very quickly. The total amount of energy we're talking about is negligible compared with the traction pack capacity, so I can't see the car's range being measurably improved. Quiescent power draw of the dc-dc is perhaps also minimal(?).

Full depletion of the 12v battery should be very rare, and usually the result of some mistake rather than simply running down the 12v battery by playing the stereo too long.

A solar-powered float charge of the 12v battery would certainly work for long-term storage, but a simple temporary attachment to the 12v battery through a regulator would suffice for that rare scenario.

Has anyone done the math?

(Sorry to be uh, I believe the expression is - "stick in the mud") :?
 
Joe - I would say 1.) Because we can, this car begs for modifications. 2.) More seriously, the factory 12v battery is a bit of a pig taking up a lot of space and needs maintenance. If you haven't checked your battery lately - probably be a good idea to do so soon. 3.) With the low requirements our 12v system needs something smaller, lighter and more compact would have several benefits.
 
JoeS said:
Um, exactly what problem are we trying to solve?
I'm wondering about that too - If you have issues with the 12 volt battery going dead, I'd look to find what problem is causing that, rather than redesigning the car to fix a problem elsewhere. Reports here of problems with the 12 volt system are very rare and are usually solved by replacing the failing battery, just as you would in any other car

As soon as the existing dc-dc is energized, it "fills" the (already almost full) 12v battery very quickly. The total amount of energy we're talking about is negligible compared with the traction pack capacity, so I can't see the car's range being measurably improved. Quiescent power draw of the dc-dc is perhaps also minimal(?)
I would think if anything, this 'solar mod' would probably actually hurt your range - In order for the sun to reach the solar cells mounted on the dash, I would have to forego using the panels I put up whenever I park in the sun which keep the sun's heat out of the car's interior, thus I'd need to run the A/C on MAX air for 5 minutes or more to cool the interior - THAT would cost me more juice than the solar panels provide

Any 'solar solution' which requires me to park the car in the sun is a non-starter here where I live

Don
 
MLucas said:
Joe - I would say 1.) Because we can, this car begs for modifications. 2.) More seriously, the factory 12v battery is a bit of a pig taking up a lot of space and needs maintenance. If you haven't checked your battery lately - probably be a good idea to do so soon. 3.) With the low requirements our 12v system needs something smaller, lighter and more compact would have several benefits.
I agree that reducing the existing i-MiEV 12v battery volume would free up a bit of room. I consider the space under the front hood as a not-very-elegant packaging job, anyway - and, what's worse, everything under that hood gets wet when I wash the car.

The photo below shows my Headway LiPO4 12Ah four-pack that I use for hobby tinkering. It has three connectors: JST-XH used for the CellLog8S for cell monitoring and low voltage alarm, the JST-PA to interface with the PowerLab8 cell-level charger/balancer, and the Anderson PowerPole for the I/O through a 30A fuse.

Headway4S.jpg


My i-MiEV puts out 14.26v at around 75degF, measured at the accessories outlet. This is pretty darn close to the Headways' 100%SoC of 4x3.65 = 14.60v and, although safe, I wouldn't like keeping it at this voltage all the time as a decrease in one cell would drive the others into overvoltage if not controlled by a BMS.

Inasmuch as I don't have a distributed BMS (which I would put in if I were to install this Headway pack into the i-MiEV for any length of time) I presently top-balance this pack using the PowerLab8, and then monitor it using the CellLog 8M or 8S which has a cell-level low-voltage alarm. The problem with keeping the CellLog permanently attached is that it draws a minute amount of current and over time it could unbalance the pack.

If this pack were to get partially depleted in the i-MiEV, it could easily draw the full dc-dc converter output current (60A?) as its internal impedance is significantly less than the OEM FLA battery so I'd have to use a larger fuse. Dunno if I'd want that.

My preference for the i-MiEV battery replacement is a nice small (~15Ah?) AGM VRLA sealed unit. Since my i-MiEV's 12v battery is still going strong and shows no corrosion, this project is on the back burner... I hope it dies so I can stick in the AGM as I hate flooded lead-acid. I kept an EV conversion with 24 golf-car batteries in my garage over a winter a few years ago, and the outgassing fumes put a layer of rust on all my tools and equipment.

Back on-topic, on my presently-unused ICE vehicles outside (under covers), I use small 15W solar panels feeding the 12v batteries through regulators as that's less work than pulling out their batteries. A couple of those batteries are 20 years old and still provide sufficient starting juice!
 
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