Solar Solution for new "bike".

Plissken

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Feb 28, 2021
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My new bike is finished now, and I would like to start a project for solar charging it.
Problem is a don't really know anything about solar chargers.
It's a 72v 8000w bike. I believe it runs at 200amps peak. The battery is quite large. I would like a solar setup with it's own battery bank, that would allow me to plug in and charge the bike quickly, then leave the solar system to top up it's banks for next time. The idea is not portable, but simply independent of the grid.


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The key thing will be limiting charge current (and obviously voltage) when you are charging off a bank of batteries. Your existing charger should be the template for maximum voltage and current.

Alternately, you could put an AC inverter to produce line power, and simply plug your current charger into your solar system. This requires less engineering on your part.

Your solar system would then be:
Solar panels and rack to hold them.
Multiple inexpensive deep cycle lead acid batteries.
MPPT solar charge controller.
AC inverter to convert the DC of the batteries to the AC voltage your charger expects, make sure it meets the current required by your existing charger.
And... of course, your existing battery charger.
 
Ok thanks. I ordered an MPPT that allows multiple inputs for solar panels, a 2500w inverter and a battery meter and storage crate.
Might as well build it overkill, and it can also server as an emergency backup for the house.
Once the crate arrives, I will check how many car batteries will fit in it, and then look at solar panel options. Not sure yet if I want them permanently mounted on the roof, or something that can fold away. It might be a good idea to have the option to move it, even if I don't intend to do that.
 
I used to have a small solar generator (400W) with (12) 12v 100Ah batteies in parallel for an off grid cabin. I have worked with DC power for over 25 years in telecommunications. The system addertooth described is that same I would recommend. I made an A-Frame for the solar panels which I could reorient to get the best sunlight for the time of year. I think using 12v systems are easiest but cable can get costly if your panels,batteries, equipment are far away from each other or the house. I would also recommend pure sine wave inverters. If you are tying into your house for back up, you will need to think about what you want to have backed by battery. If you try to have your entire house backed up, remember your reserve time is limited by your battery capacity. There are a lot of laws regarding solar panel systems and connecting it to your house safely. You'd need an automatic or manual transfer switch which isolates your house from the grid. Home battery banks are illegal in some states.
 
I'm curious about the DC-DC option though. Inversion does shave off 10% or so efficiency. I'm not an EE, but if the battery bank was the same voltage as the bike, wouldn't a mosfet or two in series in the charging port be all that is needed? This is a question not a statement.
 
I'm curious about the DC-DC option though. Inversion does shave off 10% or so efficiency. I'm not an EE, but if the battery bank was the same voltage as the bike, wouldn't a mosfet or two in series in the charging port be all that is needed? This is a question not a statement.
It is complicated. Chances are the deep cycle lead acid batteries connected to the array would not be at the ideal charging voltage, due to a different "per cell voltage". You also must have current limiting when charging Lithium batteries. Simply drawing power from the lead acid batteries would have no current limiting. Finally, the charge needs to switch off when the Lithium bike battery is at full charge.

Occam's Razor: What I proposed was the most simple answer which did not require an EE to design you a custom circuit to be built.
 
For using it as backup power to the house I would likely just run an extension cord to the fridge. Nothing else is really that important. In case of emergency the last thing i care about is a TV or computer. Just keep the food from spoiling and we can cook on the grill if needed. And if we really did need a computer, or need to charge our phones, there would be plenty of power for that even just off my bike itself, but the inverter i got has 6 ac ports as well and a few USBs. If it's an emergency I might charge my laptop on it, but i would not be running my desktop. So overall we are talking about a pretty small load.
 
I built this for camping. I've also used it to charge our e-bikes and when we have had power outages here at the house. A 300 ah LiFeP04 battery is in the bin with associated electronics. The top box has a 2200 watt inverter with power strip and an outlet so I can plug our travel trailer 30 amp power cord into it. The other box is a solar panel combiner box with fuses and breakers. Depending how I wire the panels I can have between 400 to 800 watts set out. If I was to do it again I would use two 48 volt server rack batteries and all-in-one solar inverter/charger/controller
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