battery boosting with small solar charger?

[jimmyhackers]

i have a semi defunct mpt 7210a solar charger.

i was hoping to use it to boost my batteries as they are getting old saggy (voltage).
they are three 6s 12000mah lipos in series.

although they begin at 75.6v they quickly go below 72volts. id estimate there usuable h now at around 9-10,000mah

rather than buying newer or bigger ah batteries. my hope is to make a smaller 12 or 24v battery to power the solar booster and this will add a few more amps at 72vs to increase my range a little and reduce stress on the main battery.

my hope is to have it working all the time while the battery/bike is under use.

i would like any advice or help about this.

 

[john61ct]

Adding fuel to the tank a teaspoon at a time

 

[jimmyhackers]

my ebike only sips fuel anyway.

its 1500 watts divided by 72volts which is about 20 amps max draw. half the time im no where near that. which explains why my 12ah battery lasts about an hour on a normal ride.

i have done some preliminary testing with smaller batteries in several configurations. a 20ah 12v pb, a 4ah 24v 6s lipo and a 72v 18s 4ah lipo

12v -72v = 0.01amps charge rate pooey
24v -72v = 0.3amps charge rate no so great
12v -24v = 0.7amps charge rate : s getting better
24v -24v = 1.3 amps charge rate verging on ok

im not sure how defective my charger unit is, that is why i bought a different/better one for my solar setup, and this is left spare.
i could need much bigger batteries ah-wise on the input side or the unit is just poorly designed/broken.
it was rated at 600watts which should mean a much higher charge rate. it should in theory charge a 72v at just over 8amps.

although a 12v charging a 72v at 8 amps should in theory be drawing about 48amps from the 12v battery, which seems like a lot for this little unit.

in its current state it would appear i would need to make another 72v battery and still only get a 1.3amp charge rate.
over an hour ride that is about an extra 10% (6 minutes) of runtime.

im not sure if the extra 1.3amps of current would add the extra %5 of torque or if it would even be noticeable.

an extra 8amps would be though

ill try tinkering with it some more.

 

[john61ct]

Forget amps when working with various voltages.

Use watts, do the math.

 

[jimmyhackers]

1500w minus 600w is 600 less watts that my main battery has to deal with.
shame i cant get the thing with 600w written on it to do 600watts

my current battery is/was 12ahx72v= 864wh (its probably less now)

if i charge it at 600watts.....in an hour it will have gained 600wh

granted ill need another 600wh battery but thats an extra 69.4% capacity, not bad

thanks for making me do that maths this way.

 

[motomech]

I've read this several times and I'm still not clear what you are trying to do. Some sort of variation of the perpetual motion machine I guess.
I do have some experience w/ the $30 mpt 7210a solar charger, both as a solar controller and a boost charger for LiPoly.
As a solar charger, it really needs at least 48 Volts of array to be worth the effort and the MPT feature is sketchy at best. Any small clouds at all will disrupt the charging cycle and it takes a long time to get back on track
As a boost charger it was remarkably inefficient unit. W/ a lead acid deep cycle 12 Volt batt., it wouldn't really put any Current into a dis-charged 12S LiPoly pack. I think w/ 2 12 V batteries is series, I could have put 2 or 3 Amps into the pack, but not even 50 Watts.
Aside from practicing your math, I think you are engaging in an exercise if futility and would strongly recommend you just buy some new LiPoly and ride your bike.
There have been times, years ago, when my LiPoly reached the end of the service life, I felt I could have used it better and extended it's service life. These days' I've gotten so good at treating my LiPoly right that I look back and think about all the miles I've traveled and I'm amazed at the value received.
The smartest thing a user of LiPoly can do is buy it on sale, even if it's not needed and store it. It lasts forever in storage mode.
The Universal Law of "If you want to play, you got to pay" doesn't change, no matter how much math one does.

 

[john61ct]

A bank that has lost 20% of its capacity has IMO reached EoL and should be replaced.

This 7210a controller. I guess you mean MPPT type? I believe they're lying about that, but more importantly, have you confirmed it will work with a battery as input?

If so, how many watts do you think these batteries will discharge? What chemistry? What capacity? Build or buy?

What do you mean by "semi defunct"?

 

[jimmyhackers]

i do wonder some time if people actually read what ive posted.

im trying to do this
https://www.youtube.com/watch?v=tbqWFVm9cD0
or this
https://www.youtube.com/watch?v=sgrbBnoTErU

except have it charging while under use.

in my previous post i listed varations of a "battery in" and what current it charges a battery on the output. so yes it does work with a battery on the input "sortof".

a new set of batteries would be £300+. i have loads of 18650s already, atm this option is cheaper.

by "semi defunct" i mean the unit as a solar charge controller sometimes would not switch on properly/automatically in the morning when the sun came out, meaning it wouldnt charge all day unless i manually told it to start by pressing a button.

otherwise it works ok.....i have a feeling i need to put a much higher ah battery with less sag on the input side. although this is a cheapy mppt i still think it does some form of power point tracking. meaning as the voltage on the "battery in" drops, it drop its current draw to compenssate. this could explain the dismal charge rates ive been seeing.

i get there will be a lot of lost energy due to conversions but if i can get it to pump in even a few amps over an hours ride itll be worth it.

i have several electric toyys at varying voltages....if i make this thing modular enough (and get it to work) it could help on all of them.

 

[dogman dan]

Being such a simple minded dumbass, Id just buy some newer cells, and paralell them in with your old stuff. Been doing this for about ten years. It won't really increase your time at full charge much, but supporting the weak ones with a new pack will help immensely with getting the most ah out of the weak ones. Anytime you do draw more than a sip, the new pack briefly provides all the punch, which means less heating of the weak pack, and longer range from it.

I'm surely a moron, but it really works. I get it you want to try something with what you have. go ahead. But if your lipos are 2 years old, its time to support them with at least 5 ah of freshies.


Currently I have 12s 20 ah, two 10 ah packs, that are over three years old. 4th summer coming up here. They suck with each 10 ah pack delivering about 7 ah, but when I parallel one of them with the new 12s pack, they can dish out 8.5 ah. Not bad for shit that old. Pulling 30 amps max btw.

 

[motomech]

by "semi defunct" i mean the unit as a solar charge controller sometimes would not switch on properly/automatically in the morning when the sun came out, meaning it wouldnt charge all day unless i manually told it to start by pressing a button.

That is normal for that unit. If it times out(Night time) , it has to be manualy restarted in the morning. It is one of the things folks complained about in the reviews.

....i have a feeling i need to put a much higher ah battery with less sag on the input side.

It only puts out a few Amps, ilreguardless of the input Voltage. It just isn't very good as a boost converter. You would need at least 48 Volts input to charge anything in a reasonable time. Get a Mean Well, they are cheap.

although this is a cheapy mppt i still think it does some form of power point tracking. meaning as the voltage on the "battery in" drops, it drop its current draw to compenssate. this could explain the dismal charge rates ive been seeing.

The MPPT only effects the charging in the sense it's cycling. If a cloud interupts in input voltage, it stops charging. The MPPT is supposed to maintain some charging and help it ramp up quickly when the cloud passes. The MPPT doesn't work very good on this cheap solar controller.
There's tons of info on the Net.

 

[memy]

I had the 7210a and it is limited to a 10amp input. Mine is fully dead after been in service for 4 months boosting 120w (18V)solar into 6 old lipo's. (To then run a 24V inverter to run a pump on an aquaponics setup. )

The more voltage you have on the input the more watts you can boost.
Eg 22.2V in you would be maxing the 7210 out at a 3amp output at 72v.
I don't think the 7210 would last that long.

 

[jimmyhackers]

thanks for the info

3 amps at 72v would still be 216watts or 216wh over an hour. thats still about a 25% increase on capcity.
shame this unit isnt playing ball atm.

despite "the internet" my unit would sometimes automatically turn on and start working in the morning. it IS a function of this unit but sometimes it would not activate. this happened due to it registering an incorrect voltage on the output/battery side, it would see the battery as full/over full and not begin its charging state.

this could be partially fixed by setting the fan speed on it to max. the extra draw would sometimes dip the voltage low enough for the thing to start charging but not always.

 

[john61ct]

Soon as a cheap component starts to misbehave like that, recycle it, life's too short your time has value too

 

[billvon]

i have a semi defunct mpt 7210a solar charger.
i was hoping to use it to boost my batteries as they are getting old saggy (voltage).

1) The MPT7210A sucks. I've never gotten it to work well.
2) If your batteries are saggy, then your problem will occur under load, when the extra few hundred watts you will get won't matter much. You could get the same result by limiting your throttle by say 5%.

 

[jimmyhackers]

with some further experimentation.

i have managed to get it to charge from a 12v (pc psu) upto a 72v with a max amps of 0.7 (50.4 watts)

it would appear i was correct about needing a much larger ah battery on the input side that would sag less.

even the pc psu sagged from 11.99v down to 11.5v

i have a 6ah 6s lipo charging currently and i will test it on that once full. hopefully ill see 1.4amps charging current (100.8watts)

i think your right john61ct/billvon, the concept i have is a good one....... but the equipment i have (the dam mpt 7210a) isnt.

i might get one of these or something similar to replace the mpt7210a
https://www.ebay.co.uk/itm/12A-600W-DC-Boost-Input-9-60-output-12-72V-adjustable-Good-for-car-amp/273598495289?hash=item3fb3bdba39:g:gioAAOSw3bZcCern

 

[john61ct]

No, the concept is shiite too.

It really is simple.

A nice big pack sized for the max discharge rate at the capacity you need, quality cells bought new and well matched.

Control systems to ensure balanced cells, temp cutoffs and not exceeding OV or LV specs.

A charger to refill it as quickly as you need but not too fast.

Ghetto / redneck workarounds like you're playing with are IMO a huge waste of time.

Better spent earning a lot of money rather than trying to save a little.

At best a fun hobby science experiment.

 

[jimmyhackers]

anyone else think johns a bit of a "lady parts"?
tbh the nay saying just spured me on to prove people wrong, so thanks

i have just tested the charger with the larger 6ah 6s lipo on the input.

my suspicions were correct, i did need a larger ah battery (6s 6.6ah lipo) on the input side. the unit will now push just under 3amps into the battery. so roughly 3x72v which is 216watts.
seeing as this battery has 24vx6.6ah = 158wh
i will need to make a larger one, 8 - 9ah for the final rendition. so about 24 18650 cells in a 6s4p llipo

so regardless of opinion, this thing works as I intended, it will reduce stress/load on any battery (NEW OR OLD) aswell as increase overall range.

also it can be used on any other toy i have aswell as my ebike, like my 24v mini moto or my 24v scooter. or my 72v mini moto dirt bike.

it post up pic when i have the final rendition done, it looks like it will be about the same size as a 12v 20ah pd battery.

 

[john61ct]

yes but just a bit

sometimes needed to drive the point home

sometimes kludges turned out to be unexpectedly useful

in this case just my opinion, but I really think it's a dead end, so trying to help you be more productive

in case practicalities are your motivation

if not, proceed as you like science experiments are fun, can be great learning experiences

 

[jimmyhackers]

here it is, half done. I put it next to a 20ah lead acid for a size comparison, a little bit bigger (only taller) but it weighs a lot less



its a 6s 8p 16ah, so about 384wh.

i just need to neaten up the wiring, add a switch, add a front plate and maybe paint it.

 

[memy]

Hmm I understand what your doing but it would have been more efficient to just reconfigure the "6s 8p" into 18s 2p and then parallel it to your existing battery. Of course you lose flexibility to boost your other toys.
I envy your available time

 

[Cowardlyduck]

Just skim read this thread...not sure if the aim is the same, but I did something similar on my recumbent commuter.

This is just a 40W 12V panel hooked into a small DC-DC converter to boost it up to 58V for my pack. It's not very efficient, and the best I see is about 17W charge, but I leave the bike outside charging all day so it adds up. On a good day in summer with north orientation I can get over 75Wh charge which is about 6-7Km range. Not bad for something that makes my bike more aerodynamic and efficient when cruising with about 20-30W less power draw as a result.
When riding I generally commute in an orientation that helps point the panel towards the sun causing the charge rate to fluctuate between 5-12W. Even with this the most I ever see from the commute portion of the charge is about 1-3Wh, which makes sense considering my commute is usually only about 15-25min.
It also has the added advantage of slightly extending the life of my battery, so I feel it's worth the effort when all is said and done in my circumstance.

https://endless-sphere.com/forums/viewtopic.php?f=6&t=57751&start=275

Anyway, just wanna point out that this idea can work...you just have to have more realistic (aka lower) expectations for what it can achieve.

Cheers

 

[jimmyhackers]

i like the solar bike.... i might put some panels on my akira bike when i get round to making it.

i get that a 18s2p will probably be more efficient than this contrapration but itll be far less configurable. my box does have some benefits over it other than being able to be used on various other toys.

i dont use a bms on any of my batteries....just a balance charger (isdt 600w)

with my current 72v batteries i actually use 3x 6s in series. but i charge in parrallel. before i connect them in parrallel to charge, i do make sure each cell is ok (withing voltage range). this is a bit of a faff and takes a minute or so.

with my box i can just plug in the large amphour 6s battery and balance lead, if it was a 72v 18s battery id have to go through this faff again or resort to a "dreaded" bms and buying a 72v charger.

another point is although my three rc lipo pouch cells are rated to 4.2v and 30c.
my 18650's.....are dubious and are more so probably li-ion than lipo and should only really be charged to 4.10v,they also have a questionable 1-2c discharge rate. id be hesitant to just connect them in parrallel as in theory as they have different discharge curves which also could make their own inefficiencies.

also a 18s 2p would be less dense in the avaiable area i have to work with than the 6s 8p i have made.

 

[jimmyhackers]

quick update.....ive been testing it out for a while now......

i have less voltage sag, and longer range. the extra juice is also noticable in a little bit more umph under acceleration.

all in all, im happy.

 

[dogman dan]

Hey, any watt hour is a good watt hour. Just a problem to carry a huge panel able to put out big watts.


I have two tiny little 30 watt panels for my RV, pretty amazing what they put out when the sun is bright, and they are at the right angle. No, it doesn't run my air conditioner, but it sure keeps up with a TV. Same watts into a bike battery would extend range more than you might think. About same as I ever can pedal up watts. That's worth it.


But eventually, better everything is better. But when you can afford it can be awhile. Meanwhile, you did not waste your time so far.

 

[jimmyhackers]

its been a while,

i havnt used the magic box since i got my newer batteries over 2 years ago. mainly due to the newer batteries taking up the space the boost box was in.

now ive got a new/old 36v scooter battery i got free. its shape,size,bms and freeness permits redoing this idea. hopefully the extra voltage in means a little more boost out.

on a side note, it would be interesting to get a 2000w(ish) boost controller (cant find one).
that could take the 72v in from the main battery, and spit out a constant 72v to the controller.
i know it would be inefficient,silly, but it would be interesting to see a performance comparison of acceleration and top speed (at both high and low states of battery charge).