Solar recharger

stormdot5

1 mW
Joined
Jun 8, 2016
Messages
15
I have a 100w solar panel I'm trying to use to charge a lifepo4 battery. On my e bike I used an ebay special voltage converter to drop from 36/48v down to 13.8v to run "12v" things and it worked great. This was for things like a headlight and car style accessories.

With the solar panel I'm using something very similar but it's not providing any decent output. The solar panel directly can put out 1 to 6 amps or so with a 20v open circuit. With the converter in the way to regulate to 13.8v it only registers 0.15 amps. Any theories as to why it?

I thought maybe it was something to do with the switching of the supply and dragging down the solar panel voltage. So it was registering 20v, switching to regulate current at that voltage but as it drew on it the actual voltage was much less so no current flowed. I tried it with a capacitor to try and smooth this out but no change.

I could get an proper solar mppt charger but they all seem to be designed for less acid and go through different float, desulfate modes etc. Which would be detrimental to a lifepo4. Also they are much more expensive.

A third option is just to make/get something that just burns off any excess voltage as heat by it seems a bit archaic.
 
How old is the solar panel? Even if it's newish, it could be bad, just a little less likely. I've seen open circuit voltages at appropriate levels for a panel, but soon as you load it, there isn't anything there.

On a bright sunny day, for observed testing only, hook your 20V panel directly to a car battery. Or a partially discharged 4 cell LiFePO4 bank. Then measure the charge current. That value is sort of a best case scenario.
 
That was my first thought. That's where the value of 1-6 amps came from. 1 amp when it's murky, 6 in clear sun. Probability capable of a little more than that in ideal conditions.
 
stormdot5 said:
I have a 100w solar panel I'm trying to use to charge a lifepo4 battery. On my e bike I used an ebay special voltage converter to drop from 36/48v down to 13.8v to run "12v" things and it worked great. This was for things like a headlight and car style accessories.

With the solar panel I'm using something very similar but it's not providing any decent output. The solar panel directly can put out 1 to 6 amps or so with a 20v open circuit. With the converter in the way to regulate to 13.8v it only registers 0.15 amps. Any theories as to why it?

I thought maybe it was something to do with the switching of the supply and dragging down the solar panel voltage. So it was registering 20v, switching to regulate current at that voltage but as it drew on it the actual voltage was much less so no current flowed. I tried it with a capacitor to try and smooth this out but no change.

I could get an proper solar mppt charger but they all seem to be designed for less acid and go through different float, desulfate modes etc. Which would be detrimental to a lifepo4. Also they are much more expensive.

A third option is just to make/get something that just burns off any excess voltage as heat by it seems a bit archaic.

Can you link to the converter your are using?

Checking panel:
check the open circuit voltage - should match whats on the nameplate, or close to
check the short circuit current - short the panel leads and check the current (on a sunny day) is close to the nameplate value.
if both match the nameplate values the pannel is pretty much fine.

what is the converter output hooked up to when its only pulling 0.15A?
Whats the panel voltage when hooked up to the converter?
whats the output voltage of the converter no load and under load?

You could always hook up a 12V 50W light globe to the output of the converter and see if it can run that on a sunny day...

my guess however is the converter is trying to draw too much current, that pulls the panel voltage down to the point it provides no power at all.
 
What voltage are you charging to? 12v ones of low amps suitable for 100w panel are quite cheap. under 10 bucks. https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1311.R10.TR11.TRC1.A0.H0.Xsolar+charge+controller.TRS0&_nkw=solar+charge+controller+10a&_sacat=0


I fail to see why any of the lead charge routines would be harmful to lifepo4, in 4s. And, not so sure the cheap solar controllers do much more than float it.

Bet it is something to do with the converter.
 
Do you still need help with this? I did a 90W solar charger ebike with a 500W motor and like 36V 16aH Li-ion batteries. I researched this a lot and a specific MPPT controller ("true MPPT") worked out real well. I have no need of mine anymore since I retired the solar bike. This controller is mppt and puts out charging voltage from 24-72V systems.

https://www.amazon.com/MonkeyJack-Waterprrof-Controller-Regulator-Intelligent/dp/B06XY27K2X/ref=sr_1_9?keywords=solar+boost+controller+mppt&qid=1569204387&sr=8-9
 

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bakaneko,
That is the same controller I use for my ebike charge station.
My solar solution is not mounted to my trike, but instead is a home charge station that I use for my two etrikes when parked.
Great controller......using with 100W panel to charge 18ah 36V ebike battery.
I'm putting into the controller a maximum of 102W (16.3V @ 6.3A). This delivers 41.6V @ 1.83A).
This figures to about 76% efficiency.
MPPT controller programs to 24V/36V/48V/60V/72V packs.....has custom pack voltage also (I use this for my 11S pack).
Current is not adjustable. Current output is a function of charge output voltage and directly proportional to total solar input watts.
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You should get a 100-150W flexible solar panel and mount that to the top of the trike. That solar panel will provide power and also a sun and rain shield. Man, that got me thinking of doing that again but with the trike. But, I feel hesitant with a trike due to visibility on the road and hence safety. Jeez making a nice looking one would be so sweet... I would do pedal assist
 
The trike was a fun project. Good idea concerning mounting up a flexible panel.
150W could push it along at around 10MPH in current configuration.
I built it light and agile (it rides like a go-cart), I love riding it in the 2-mile long twisty section of a walking/biking course close to me. So I will keep it as is for now.
The Q128C motor that I laced up to a 20" wheel draws about 600W with a fresh pack. 22MPH top speed.
I got chewed out once by a motorist who pulled up next to me at a light for not being visible enough. I headed his warnings and ride with TWO 7ft bright yellow flags (seat sandwidtched between them) ever since.
Ride safe!
PS: If you build a trike, be aware that aluminum frames can present problems for e-builds. I went with a good-old reliable chrome-molly setup. Cheap and bullet proof. Lateral force abuse is something that regular e-bikes dont have to be too concerned about, so that gives you more frame options.
 
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