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E-Bike

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solarnewbee:

Purchased an E-Bike last year in the Philippines at the behest of the wifey (boss). 3 wheels with 1 seat up front for the driver and 2 benches in back for 4. 48 volts with 4 100ah 12v gel batteries. The electric motor is 1kw hits a whopping 38kph and claims 120km range. Fully loaded up it barely makes the hill out of our neighborhood at 11kph but it gets us where we need to go. We charge it at 6am to 11am on solar and forbid afternoon and night charging as doing that it sucks the lfp’s (800ah worth) down quite a bit.

So, the boss shows me a solar kit available to install on the roof of this E-Bike. It’s only 100w and probably 12v and comes with a charge controller (pwm most likely). Not seeing how that’s going to charge a 48v system, those numbers don’t work. Seems more of a gimmick really. Then I thought, I finally got the 2 panels that arrived broken from China replaced and just 1 would be just a little bigger than the E-Bike roof. 300w 72cells 36v.

Any ideas guys how to make that work? Multiple charge controllers, 1 for each batt? I’ve got some microinverters maybe drive the charger that came with the bike? Hmmm.  2 panels sideways at 72v with flashing warning lights and a a helmet for my big head?

Looking forward for your input.

MadScientist267:
Sounds nice SN...

Only input I got other than that is that I've been messing with hoverboards and all I can say is however they calculate range, someone didn't have their equipment calibrated lol... But bikes may have much better results...

That said I have been messing with ways of increasing range without making major mods to the board itself, and one of the methods I've messed with involved one of those little 120W microinverter jobbies... All I can say there is I'm not impressed with all the conversion losses involved... And they add up quickly.

In a nutshell, go as "direct" as you possibly can and equally, avoid "repeating" conversions (like "one per" concepts). Both will eat your source alive, particularly small scale.

Look forward to seeing what you come up with tho... And a pic?  ;)

Far as the behest... Lol... All I got ;D

Steve

solarnewbee:
Here it is in all its glory 😝 as well as the old trike.

A look at the panels on the front. 10 more on the backside.

Shooting for next year for permanent move there so I can get out of the rat race.

Pete:
Hi Newbee, not sure how it would go but maybe you could use a buck converter to boost the panel voltage then use an MPPT controller to charge the batteries that way.
Or maybe try charging the batteries as two 24 volt banks using diodes as blockers from the regulators so that the two banks aren't connected together.
Buck converter probably easiest.
The machine looks pretty big, I am guessing that the 38klm it is rated at is downhill with a tailwind.
Maybe you could change the gearing if it has a gearbox to get up hills better, or put  a hub motor on the front wheel to act as a hill assist.
Have fun, the Phillipines sounds hot to me, but some like it that way
Cheerio
Pete

MadScientist267:
Pete -

I'm assuming you mean "use a boost converter to boost", not buck...?

Either way this would have "negative gains", as MPPT isn't compatible with that type of scheme.

SN -

There may be some boosting type MPPT converters out there commercially available, I haven't used or seen one personally. That isn't to say they don't exist.

That said, years ago I was messing with what I was calling "pseudo-MPPT" in combination with a home brew buck converter. Boost would be very similar, just rearrange a few parts.

In a nutshell, MPPT relies on conversion topologies to work by allowing the input (PV) voltage to be different from the output (battery and load) voltage, so that the PV can operate at it's ideal voltage to extract as much power as possible from the panels. A simple standard converter in front of the MPPT will negate it's purpose because to do it's job, it needs to regulate the voltage at it's input. Normal converters aren't concerned with this, only the output.

True MPPT is relatively complex because it has to regulate input voltage, output voltage, in some cases output current, and have a means to find the peak availability (typically done with a computer controlled "sweep" or other algorithm that lets/makes it periodically seek the sweet spot).

The pseudo version isn't as efficient at it's job as the real thing, but is better than direct connection or buck alone, and boost alone would just try to drive the input into the ground, giving you "less than useless" results when it comes to trying to charge a battery with it (this side of it is a little more difficult to explain).

Pseudo basically gets set up so that it's approximately in the middle of the PV's typical sweet spot (using a simple pot), and tries to hold it there. To do this, the feedback of a standard converter is basically just moved to the input "instead of" the output.

There's a catch however, hence the quotes above... You'll still want it to respond to the output voltage of course, to limit the maximum voltage the battery and load sees... But it's not too incredibly tricky to make a simple "mixer" that allows you to set both, if the chip controlling the conversion doesn't have 2 inputs (MC34063 vs TL494 comes to mind, for example).

It's still not a "super simple" solution, but is far more simple than a full blown MPPT to do from the DIY perspective.

Just a thought.

Steve

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