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DIY Ebike solar battery charger

capnnak

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Apr 18, 2020
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I want to charge my 48v Lithium ebike battery via solar. Not a bike mounted system, rather go out and ride then come back to camp and connect my ebike battery and charge it. The current system I use is to plug in my 110v ebike charger to my 110v AC port on my Goal Zero Yeti1400. But, I don't like having to convert DC to AC then back to DC - how inefficient. What I want is to connect my portable 200w solar to a charge controller then to my ebike battery. Can this be done? The ebike battery has a 5mm barrel connector. The battery is Lithium Manganese 48v. Ebike is made by Rad. The solar panel is 200w Goal Zero Boulder with APP connections. I was thinking I could connect a Victron 100/20-48v to the solar and then the bike. Can someone please advise? -Don
 
One thing to watch out for is whether or not the eBike will only accept the 'official' charger. My eBike communicates with the charger first before it will begin charging. If you only have a single barrel connector then you'll probably be OK.

Charging from DC to DC is absolutely possible, and more efficient, as you say, than inverting to AC first. LMO chemistry requires a 4.2V per cell charging voltage and can safely accept a 1C charge rate.

The Victron 100|20|48 will work, though quite the expensive option for what is essentially a 'hack'. You might want to consider buying a cheap CC/CV boost converter module (loads on Amazon/eBay - search "CC/CV boost"). They usually go for around $30 or so. Barrel connectors are dirt cheap and are usually specified by their size e.g. xxx5525 will be a 5.5mm long, 2.5mm wide jack. If you buy one without a display, you'll need a multimeter to set it up initially.

You will need to find out exactly how many cells your battery pack has. With a nominal voltage of 3.7V I'm guessing a 48V(nominal) pack will have 13 cells. But check! Once you know the number of cells, you know what CV to set the module at e.g. 13 cells x 4.2V = 54.6V.

If you do go via the CC/CV module route, I would recommend buying one with at least twice the power you actually need e.g. If PV = 200W, buy module rated for at least 400W.
 
Before you go to all the trouble to do this, keep in mind, you are using a low wattage draw charging the bike, and the AC side of the Yeti is very efficient. You really aren’t saving much.
 
and the AC side of the Yeti is very efficient.
How do you know this? Not challenging it, just curious. I just went through GoalZero's website and read a couple of the user manuals for the various Yeti models and found no actual specifications for the inverter efficiency, bar a few comments here and there that their inverter was, "highly efficient".
 
How do you know this? Not challenging it, just curious. I just went through GoalZero's website and read a couple of the user manuals for the various Yeti models and found no actual specifications for the inverter efficiency, bar a few comments here and there that their inverter was, "highly efficient".
My meaning is with the low wattage of the bike charger, there isn’t much loss.
 
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