Solar charged ebiking!

[veloman]

John in CR has a great point!
I'd definitely recommend running the solar charge controller to an intermediate battery bank and using a proper balancing charger for lipo.

my current booster pack is 3s15ah lipo. I bulk charge everything at once and monitor the cells every hour, and more often at the end. I stop at 4.12/cell or so. It's only 1amp, so it can't charge very fast.

But I see your point, for the person who can easily forget. It's just nice to get 99% of the panels output into my battery. Even my mish-mosh power cable with 5 sets of connectors only looses 0.01amp.

 

[t3sla]

''Micro-Inverter is an innovative solution for solar installations. It directly converts the DC voltage solar power from PV-panels into standard AC grid voltage (230V/50Hz). The micro-inverter is usually mounted directly at the solar panel. The input (DC) is 20V to 50V. The power of microinverter is usually 250W. (The inverters bellow 1kW of power are in general called micro-inverters)''

I thought about using one of these because I already have BMS/SmartChargers

GWL/Power GridFree Micro AC Direct Invertor DC-AC 230V, 230W CE
http://www.ev-power.eu/GridFree-Inverters/GridFree-Micro-AC-Direct-Invertor-DC-AC-230V-230W-CE.html

Datasheet
http://www.ev-power.eu/docs/pdf/GWL/GWL-MAC230A-Spec.pdf

Seems a quality simple solution, but not efficient as DC-DC

 

[ddk]

...
Why the need for CC/CV?

I ain't John But the need for cc is to guarantee staying at, or below the charge c-rate of the battery, whereas cV sets the final pack charge voltage.
For instance, I use a 500W power supply set at 41.5V to bulk charge my battery packs. The packs use 5000ma 2C-rated battery cells in 3P or 5P configuration, or 6C- 10C capable.
500W is well below the c-rate of the battery packs and 41.5V being the (fixed) voltage, where the battery draws (close to) 0 current when equilibrium (41.5V) is achieved.

So the way I think about it is more along the lines of a cV charger, since 6C-10C is far more current than my power supplies can output.

I can wire my panels in series for 40-something volts. But as I mentioned before, I regularly use intermediate 12V gel-cell batteries powering rc battery chargers
The ability to quickly rewire the panels for series connection and direct pack charging is for those times when things break down, as all things eventually do.

You can get MPPT chargers for lithium cells, but at this time they're pricey... which makes little sense because charging a lithium battery is far simpler than charging a lead-acid, NiCd or NimH cell

 

[John in CR]

John, what do you recommend to use for a HVC? Right now I like to stop at 66.5v, but will be changing my booster pack to 7s headways, so more like 78v. That's 5v under 3.65v/cell, or 3.4v/cell end.

I thought I posted the schematic of Fechter's HCV circuit....a few resistors, a few diodes, a transistor as the switch, and a common regulator.

Why the need for CC/CV?

Reverse sag. Almost all chargers have the current taper off at the end. Otherwise if you send significant current, then as soon as it turns off it will come back on. The HVC will be so small and cheap, with a 2A max anyway, that I'll have one for each .5A of series strings. Then I'll just stagger the HVC's so current tapers off near the top of charge giving me the CV part of CC/CV.

The HVC's will use only a miniscule amount of power with the current flowing from the solar cells through a diode and a PNP mosfet to the battery, and the resistors sucking off a tiny bit so the regulator can trigger the switch to turn off when the voltage is reached. It just doesn't get any more efficient without you acting as the switch. For a pack with a BMS you could just connect using only a diode, but you'd be relying on the BMS to block additional charge. It's tempting, but Justin looked at that and decided it was too risky.

John

 

[ddk]

...in the cV charge world, the battery's SOC tapers the current and the (bulk charge) power supply has nothing to do with that.
So, set the maximum output voltage of the power supply, unloaded, to the battery's desired EOCV (end-of-charge-Voltage) and wait until done.
for fun- If your power supply happens to have a current meter, watch what happens to the output current as the battery charges.
Barring balance chargers, this IS the safest way to charge a LiPo battery pack.

John's right about panels being cheap btw. Need 100V? Simply wire up more panels in series (check the panels "Max series voltage" rating, however)
-however-
I allude to some obstacles to just 'tossing a few more panels on the roof'.
I prefer MPPT devices over the other, more primitive and less efficient methods of transferring solar panel output to battery. Living in fogland I appreciate how well my systems work on those many less-than-optimum solar charging days.
finally (whew- about time I shuddup)
There are several different ways an MPPT device senses state-of-solar panel, but they all work better (more efficiently) than a simple circuit.
Heck, even a pwm charger works better than a simple 'off-on' type switch (for lead-acid, at least)

 

[veloman]

Well my 48v aluminum charger quit the other night. I put it on for 3 minutes and it just sputtered and shut off.

So the solar panel is a huge help now. But it's not quite enough if I am traveling a lot, so I needed a replacement charger for the 50v a123 pack. I strung 2 chargers in series for top voltage of 53.7v. One is a 24v 2a lith-ion bionx charger, the other is a 24.3v max laptop supply at 2.6a. At first I thought it was putting out 7a as that's what my multimeter said, but that didn't sound right so I plugged it in using my killawatt meter to check power consumption and it's 75w and 55w for the chargers. So I'm probably right near 2amps or so. Yay, I got a charger to work.

Check out how ghetto this is.... will clean it up tomorrow.

 

[amberwolf]

Just for grins, have you tried a different AC cord on the bad charger? I had a similar-sounding failure of mine, and that's all it was. Bad connection from badly-made cord/plug.

 

[veloman]

I tried another ac cord too. I can hear the sparking when i plug them in.

I got another lot of solar panels coming. These are unisolar flexible type, very cheap near 50 cents/watt. Could build a velomobile shell with these on top.

 

[ddk]

...
nXt is a terribly mis-speced mppt controller that may or may not be what it's supposed to be
LOL- I dunno !
-but I bought three, expecting delivery in mid Feb

:lol: Hugo canceled the order!

I wonders why...[knodknod]

 

[ddk]

I tried another ac cord too. I can hear the sparking when i plug them in.

I got another lot of solar panels coming. These are unisolar flexible type, very cheap near 50 cents/watt. Could build a velomobile shell with these on top.

The issue I have with all flex panels is their miserable efficiency compared to poly or mono-crystalline cells.
But if ya gots the space...

 

[veloman]

These are quoted at 7.3watts for a 9"x 14" panel. That seems roughly the same power per area as the other rigid cells I've been dealing with.

 

[ddk]

1.2W per x sq in vs 1.2W per x sq in = yer right!
maybe I was remembering cost differences or sumtin...

Such as the panel I linked earlier in this thread that costs almost twice as much per watt as what I gave for my 300W panels. ($230 per 135W vs $300 for 300W)
but, like everything else these days, things change rabidly.