MPPT Solar Charge Controller (SCC)

[dkcomm]

Hello everyone, this is dkcomm (Don) once again. This is my second post and I can't get enough of you folks and your expertise! My other post, my first, was to ask a question concerning PWM charging of LiFePo4 batteries (24V, 10AH). Your responses were immediate and excellent! As it turns out my tinkering has produced a bike that has about 10 miles range; a speed of about 18 MPH (Max, level); and, with the flip of a switch, can be driven by an 85 Watt, 24V Solar Panel ALONE (again level Gnd.) The motor is a geared 450 Watt Brushed motor that is quite good on small hills driven by the 24V - 10AH battery. One of my main objectives was to have a PEDELEC (Not strictly electric only), and this configuration has turned out surprizingly well! It is especially satisfying when I get up to crusing speed in bright sun (I live in Florida) and flip the SOLAR ONLY switch! Wow! With minimum input from me the panel drives the motor quite nicely and I sail along on Solar power, i.e., no batt - there is something very exciting about that!

Now, I would like your expert advice once again. I want to use an MPPT type solar charge controller for the battery. Currently (no pun) I use a very inexpensive 12V/24V PWM controller, CMP-xx something. I do need a battery every once in a while... I used a heavy duty (junk) relay to do some switching and the protective Anti-EMF diode across the coil came loose. Since then the CMP-xx has acted quite funny; I think it was zapped. I do not trust it with my expensive LiFePo4 battery, so I want to graduate to Maximum Power Point Tracking (MPPT). I know they are out there in scads but they are expensive and in my case some overkill. (I don't need waterproof, I don't need 30 Amp for example (15 only), etc.)

So, which is the best, inexpensive (very) controller I can get. Best and inexpensive is probably a contradiction in terms but I need something ... Can anyone help?

One last thing. Somehow, somewhere I am going to get a 3-wheel adult bike. My electronics, motor, etc. will be transferred from the existing "normal" bike to the 3 wheeler. I don't have much choice in that; I am 72 and have enough titanium supporting my spine the Russians could build a sub out of it! So, sooner or later, I must get a 3 wheeler. I expect to get similar, perhaps even better results with that configuration. I will have 2 solar panels on it. I was able to secure 2 85 watt 24V (36.5V) panels quite some time ago, but can use only one (and that's a little shakey) at the moment.

Many Thanks Again,

Don

 

[parabellum]

What is "inexpensive" in your mind? Battery of which chemistry do you want to charge?
I have good experience with Morningstar MPPT's.

 

[dkcomm]

Hi,

Thanks for the response. As mentioned in my post the battery I want to charge is a 24V, 10AH LiFePo4 battery. As long as I keep within the voltage and current ratings I can use just about any method of charging so long as i do constant current then constant voltage. Up til now I had a 12V,24V auto switch Pulse Width charge controller. But as noted, I think I zapped it with a large counter EMF pulse from a realy coil. I have to replace it so I want to replace it with a better charging tecnology, hence MPPT. The 24 volt high and low set points on the former PWM controller were right where I wanted them for my LiFePo4 arrangement. If the set points for the MPPT are not different (they should not be) then that is the way I want to go.

Since the quality of my and my wife's entire life (home, utilities, food, dog, etc., etc.) comes from 1 Social Security check my "Playtime" with my electric bike (trike, vehicle, whatever) is way down the list. $30 would not be too much but I have never seen an MPPT controller for that price - especially Morningstar and that quality of controller. Actually, that's why I did this 2nd post... I could not find anywhere an MPPT controller I could afford; I thought mybe with all the resources out there in this forum someone might have come across such a controller. Thanks for your interest parabellum and to anyone who might be able to offer some hint in my search.

Don

 

[dak664]

Well you really do not need MPPT for charging a battery. Since batteries are charged by current, maximizing amps through the battery amounts to the same thing. The addition of a coil and diode before the current measuring shunt of a PWM controller does that for a couple of bucks. Pre-engineered chips can do it, or you can roll your own with a microcontroller, but in either case you have to breadboard it yourself. Google solar battery charger buck converter for manufactured sub-US$10 chargers, and if you find one with a credible guarantee go for it

 

[Jeremy Harris]

MPPT does make a significant improvement to charge power from a given size of solar array, I've found, but getting an MPPT that's optimised for lithium battery voltages isn't easy.

I bought an Australian made relatively low power MPPT for my solar powered boat, that allowed the output voltage to float to whatever the charger needed, so I then had to add a charge controller to keep the maximum voltage within limits. Unfortunately, the MPPT I bought isn't in production any more.

I found that I got between 15% and 20% more charge power from using an MPPT over just connecting the panels to the battery pack with a near-zero loss ideal diode. The MPPT optimised the charge power a lot whenever the sun wasn't directly shining on the panels, which is a fair bit of the time up here at 51 deg N.......

 

[energyi]

Morning star has 24V charge controllers with MPPT: http://www.morningstarcorp.com/en/home

They have been around for a long time, good products.

Joe Mc.

 

[dkcomm]

Thanks to all, expecially to Jeremy. You hit the nail right on the head! It is the maximizing of the solar array I am seeking. I mentioned in the earlier post that I wanted to get a trike and transfer my electronics, control, and motor from the existing, rather ungainly 2-wheeler to a trike. Doing that will enable me to mount both of my 85 watt solar panels for a total of 170 watts maximum - squeezing that extra 10 to 30% out of the panel(s) charging current using MPPT will be more than enough to quickly charge my LiFePo4 when I use battery + speed controller to power the bike. I will use the same switch/relay configuration to drop the solar-controller/battery/speed-controller out and power the motor directly using the paralleled solar panals for my desired Pedelect riding.

I know that because I am using only 1 panel on my 2-wheel bike and it works well (although clumsey and rather unstable)when I change from battery power to drive my motor/trike in a very helpful PEDELEC mode.

My desire to upgrade to a 15 amp MPPT does 2 things: It replaces my "current" defective PWM controller, and it helps to offset the less than optimal angle the panels will be fixed with respect to the sun. My future plans include circuity and small motors that will vary the sun angle to obtain as much solar charging power as possible.

Please note (all): The MPPT has nothing at all to do with the direct connection of the solar panels to the motor in the direct-drive mode. In that mode it is litterally a direct connection from panel(s) to motor. I will use the MPPT to most efficiently charge the LiFePo4 battery for use in the "normal" electric bike mode.

A main thrust in my original post was (hopefully) to discover some manufacturer or company that sells MPPT technology cheap. Sure, Morningstar is excellent but it is way beyond my modest means. Almost everything I have used to build this, my first Frankenbike, is used, found thrown away, bought at severe discount, etc. Even the bike was a throw-away. The only thing I have had to buy new is the battery and I had to save months to get that. Not a sob-story; I simply cannot afford Morningstar and its equivalents.

Thanks much to all,
Don

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by Jeremy Harris » Wed Nov 14, 2012 6:07 pm

MPPT does make a significant improvement to charge power from a given size of solar array, I've found, but getting an MPPT that's optimised for lithium battery voltages isn't easy.

I bought an Australian made relatively low power MPPT for my solar powered boat, that allowed the output voltage to float to whatever the charger needed, so I then had to add a charge controller to keep the maximum voltage within limits. Unfortunately, the MPPT I bought isn't in production any more.

I found that I got between 15% and 20% more charge power from using an MPPT over just connecting the panels to the battery pack with a near-zero loss ideal diode. The MPPT optimised the charge power a lot whenever the sun wasn't directly shining on the panels, which is a fair bit of the time up here at 51 deg N.......

 

[Holocene]

Hi, you may find some deals on EBAY. Caveat: I have not used this product or this Dealer. YMMV.

Good luck!

http://www.ebay.com/itm/5A-DC-Buck-Converter-Constant-Current-Solar-Battery-Charger-LED-Driver-PWM-/281018904818?pt=LH_DefaultDomain_0&hash=item416e0830f2&ssPageName=RSS:B:STORE:US:101

 

[whatever]

I'm also looking at mppt for a charging system, can anyone explain the difference between the mppts on ebay etc,
some say pwm, some say buck/boost etc, how is it possible to tell which mppt is worth the money?
I do have a couple of old aerl mppts but they have small add on boards which are quite fragile and have broke unfortunately