Ebike batteries to help charge cabin..

Shhoom

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I’ve got a pretty simple solar system at my cabin with 60v 240w solar, an mppt (I think 20-30 amp limit) and about 100ah 12v lead acid batteries.. We only run led lights, maybe 50w worth if every light is on.

Through a confluence of unfortunate timing the panels are pretty inaccessible and getting too much shade this winter. Cabin is in a heavily tall forested location, who would have thought 60 feet up a tree facing downhill and still getting shade. Anyways, on top of that with covid the cabin is getting more use than normal and the battery bank is not getting a full charge anymore. It used to have the chance to charge up between weekends but now maybe only gets 2-3 days to recover with no load. This is all to say, I know, fix the crap that’s wrong with the system.. maybe next summer.
We can run a generator to power a 10amp charger but that is a pain in the butt, not to mention wildly inefficient. And loud. I’d rather use a headlamp at that point!

Meanwhile, I have a big triangle 1.3kwh and a mighty mini 300wh 52v battery for my ebike, and 300wh 36v battery in 100wh bricks for my wife’s bike. So I’d love to be able to top up the cabin batteries with any or all of my nice light ebike batteries.. everything has to be hiked in up the mountain. I don’t want to spend much on this because I expect to just do it this winter so a 48v inverter to power the 10amp pro sport marine charger isn’t what I have in mind.

I got to thinking about how similar the solar panel voltage is to my 52v battery. I wonder if there is a way to basically swap out the leads from the solar panels for the leads from my 52v battery.. I imagine a direct connection would blow the crap out of my mppt controller since the battery would be capable of absurdly more amps than my meagre solar panels. Or would it?

Or should I just suck it up and spend a bit on buck converter? I’ve never used one before so not sure how to size it though.

Cheers!
 
Undercharging your e-bikes batteries is also an option. It they go under the voltage of say 48v, then bring them up to 48v. Later when you have a generator or other access to a wall socket, fully charge and balance your bike cells.

:D :bolt:
 
Are you talking about getting a 48v inverter?
That isn’t what I have in mind, not looking to spend much money in this temporary stopgap adventure. I mentioned that to head off that suggestion and give the impression I have put some thought into this ;)
 
Shhoom said:
Are you talking about getting a 48v inverter?..

No. I was thinking using your solar panels in a 48v configuration to charge your 52v pack and then use that as a battery source while charging your SLA's. Anit-spark connectors are available for a few dollars so you could just disconnect the 52v battery and reconnect without spark. You would, at some point have to balance charge you 52v battery, but unless you have bad cells, that could wait for a week to a month at a time.

https://www.amazon.com/Amass-Connector-Anti-Spark-Battery-Charger/dp/B074PTHZ3M

:D :bolt:
 
e-beach, thanks... but I'm looking for a solution to REPLACE solar panels for this winter, that is, arriving at cabin with fully charged ebike battery and running without the solar components.

I'd really like to just connect my ebike battery directly to the solar inputs on my MPPT controller. But I'm afraid the battery having so much higher power than the solar that it would blow the MPPT. Or would it?

I suppose it would be similar to connecting 4000 watts of solar to a 500w MPPT controller. Power has to go somewhere, so am I correct that it would overwhelm the MPPT and blow a fuse or meltdown? What could I put between the 58v battery and the mppt to limit the current? I don't need high power, even 50w continuous would be fine..
 
Then you have to do better then "think" that your MPPT is 20 or 30 amps. You have to "Know" what the actual maximum is.

What does the manual say the maximum input current is? If you don't have the manual, what does the manufacture say it is?

:D :bolt:
 
Whether the MPPT is 20 or 30 amps really isn't preventing a general solution here, when we know the triangle battery is capable of supplying 100 amps, (or more while melting down). (The manual and box are at my cabin, I'll look it up when I'm there...) Once I know what general solution could work, I can configure/size components as necessary.

Hell, let's say my MPPT is a 30amp max so we can move on:

What could I put between the 58v battery and the mppt to limit the current? I don't need high power, even 50w continuous would be fine..

edit... i just realized although my 1.3kwh triangle battery is 100 amps, which would blow the system, my smaller LiGo battery is 36v/10amp... so can i assume I could just wire that directly on to the MPPT controller? Or would that also potentially try to run more than 10 amps.. know what, Grin are great at replying to emails so I'll just email them directly..
 
Ok, lets change direction a bit because your battery once connected isn't going to automatically discharge 100A to your system.

So, what is your actual maximum amp draw when everything is turned on?

:D :bolt:
 
The BMS doesnt reduce amp from the battery, it just cuts it when it gets too high. That being said, I thought the mppt controller limited the current based on max output...? That was how I was planning to charge a 12V battery with a 66V battery that is capable of 450A at least. I have not got around to test it, so I dont have the answer yet.... Now Im curious if I have got it all wrong 😂
 
First things first on a project like this it to know the specs of the electronics you are using.

:D :bolt:
 
Only voltage get "pushed" from source to the bank.

Current amps need to be pulled by the bank from the source.

Really, silly to charge one bank from another.

Just use a current-limiting DC-DC buck voltage converter and powertge load devices directly from your eBike packs.

Make sure you protect them from being drawn down too low, at low C-rate cut-off at 3.4V or even higher will ensure minimal impact on longevity.

Get an Ah per 24-hour budget put together at 12V, and assume the buck conversion will cost at least 15% no matter what the vendor says.
 
@Shhoom
I was recently working a similar project myself. I had an extra ebike battery lying around (52V 50Ah) and I wanted to be able to charge another battery.

In this case, since your ebike battery voltage is much higher than your SLA battery, you will need a Step down buck converter to charge your 12v SLA. I would get one that's programmable (so you can specify the output current and output voltage).

I would bypass the mppt controller all together since that's only useful if you're charging from solar (someone correct me if I'm wrong).

Here's a programmable buck converter on Amazon that I think will do the job.
https://www.amazon.com/DROK-Adjusta...+down+converter+50v+12v&qid=1611551926&sr=8-8

You just plug your ebike battery into the input, and connect the output to your SLA battery. You'll want to set the output to 12.9 volts and current 10amps. These are standard figures for charging a 12v car battery. It's ok to deviate from this slightly.
 
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