how do we charge chair using solar power?

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Re: how do we charge chair using solar power?

Postby Burgerman » 19 Oct 2021, 21:19

Its also why theres 2 connectors, and a link loop here too.

This loop is useful in other ways. Remove it and nobody can steal your chair. Better still remove it when you store the chair and then the battery does not get slowly drained by the OFF controll system. So the battery can be charged every 3 months instead of every 10 to 14 days.

It also allows you to start a vehicle, or take a FAST charge from any car, truck or bus if you need power to get home. So call you GF and out she comes with her car and away you go 20 mins later.

http://www.wheelchairdriver.com/gopro/starter.mp4 dead battery, lights on overnight.

My invacare brushless (useless) chair. Also fitted with 12/24V split wiring. Takes about 1 hour and costs peanuts. Charges as fast as your cars alternator can do it.
Also means any 12V charger can be used. And that you can get 24 or 12V out to run inverters for AC when needed too. Very flexible.
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Re: how do we charge chair using solar power?

Postby Burgerman » 19 Oct 2021, 21:25

martin007 wrote:Is the apocalypse coming?



It is for you. You voted in a bunch of socialists! That will work well...
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Re: how do we charge chair using solar power?

Postby slomobile » 19 Oct 2021, 23:16

Burgerman wrote:Theres plenty of info in doing an addon pack here.

Quite true. So much that it gets confusing sorting through the threads. Lots of times I think I am reading through solid info, only to find its an old thread with out of date info. I guess the older threads, being older, float to the top of search results, causing them to rise even further. Sticky helps, but the sticky threads get very long and polluted, and are also old info. Some sites compile the most relevant old info in a new thread, lock the thread from new comments, then sticky that. Its ok, I'll figure it out, was just going direct to question given the short timeline.

You will need to limit it to 13.8V CV and CC of 12A maximum to not damage the chairs charge connector or loom.

Then I'll use Anderson pigtails to the batteries and maybe add a presence detect wire to an XLR cable adapter to increase the current limiting in case I want to make it universal for other chairs.

37Ah at 24V nominal, is 888watts. plus 10% for losses = 977 watts of energy.
Depending on what electronix/DC DC inverter you use (like a PL8 or something cheap on ebay you could use a 36V or 48V or 12V lithium nominal battery voltage. And you may lose another 10% with the inverter so now you need around 1074 watt hours needed.
To add this to an MK lead battery in 4 hours is approx 9.72 amps to the chair.

Thanks, that gets me closer. Probably use solar mppt charger with programmable cut out.

while chair (motors and electronics) consuming equivalent 1A continuously.

But that doesent happen the battery load is varied from above 100A down to a few mA when doing nothing and everything in between.

The additional 1A draw is just an estimated value picked out of a hat to represent all loads on the chair other than battery charging. Like quiescent current, seating actuators, brief driving, but with the current spread evenly over 4 hours for easier analysis.
At 4 hours, the add on pack voltage should still be equal or greater than lead acid Voltage. This is defined as Pack Minimum for this application. What does that voltage profile look like?

Not sure what that sentence means at all.

I'm trying to define a bench testing standard to determine if a given solution is minimally successful without requiring a chair during the test. A real test would require real batteries, but batteries can be modeled for virtual tests. Bench racing. The add on pack must raise the lead acid SOC from 50 to 85% while simultaneously supplying an additional 1 amp load (carbon pile) @ 24v nominal for a full 4 hours. When the lead and lithium batteries are disconnected at the end of 4 hours, the lead SOC and amount by which lithium voltage exceeds lead is an indicator of how well it did and how much it had left to give(overcapacity). If the voltages are equal and lead SOC is still 85%, the lithium battery exactly met the minimum criteria. If lead SOC is below 85%, the lithium solution failed the test. I may have gone overboard, or chosen unrealistic values, just thought it would be useful to have a standard method for comparisons.

Chair Maximum, Never exceed highest voltage the M3 electronics can handle, but get as close as possible. Anyone know what that is, or how to find out?

Its 35V and at around 28 volts you get regeneration spikes as you decelerate that push it very close to this limit. Which causes over voltage errors to be displayed. But you wnt to be prividing a constant current of up to whatever amps you choose, with a CV level of the batteries float voltage. And if you have MKs on board or generic AGMs thats around 13.8V per battery.


That is extremely helpful knowing where the spikes rise to. 35v is a pretty common discrete component voltage tolerance which I was expecting, but confirmation is better. I may slightly exceed 13.8v per battery as it wont be above that level very long, and sluggish programming and driving should mitigate the regen spikes. Thats just me saying I'm willing to risk my batteries. Not saying it wont kill them prematurely. I've heard that gel AGM are susceptible to localized overheating when bubbles in the gel electrolyte don't collapse when overcharging But that isn't a factor in their life expectancy when kept to 13.8 because the gel resists bubble formation in the first place.

You are going to have to explain that charging part to me more carefully. Yes you can connect a LiFePO4 pack directly to a lead based chair. Many do.

I'm second guessing now. I thought I needed to be extra careful that the add on pack voltage was not too high, so I was thinking of ways to top balance at a lower than normal level. Maybe not necessary. What is the maximum pack voltage of the LiFePO4 pack directly connected to lead batteries? Do they insert any current limiting? I was looking at the possibility of avoiding current limiting by judicious choice of lead charge vs lithium discharge curves at less than maximum lithium SOC.
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Re: how do we charge chair using solar power?

Postby shirley_hkg » 20 Oct 2021, 01:11

slomobile wrote:
Burgerman wrote:Theres plenty of info in doing an addon pack here.
Certainly including this
https://www.wheelchairdriver.com/board/ ... e&start=60
.



We are group of 250 wheelchair users , mostly powerchairs.

SLA sucks and takes time to get subsidy to replace.

Therefore, we have these (plug in add-ons) , to lend to them.

They also will borrow one , when they head for a long ride occasionally .


The most compact one I've made is
240*110*170h , @24V50Ah. That's more than 1KWH of energy.
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Re: how do we charge chair using solar power?

Postby Burgerman » 20 Oct 2021, 05:19

I'm trying to define a bench testing standard to determine if a given solution is minimally successful without requiring a chair during the test. A real test would require real batteries, but batteries can be modeled for virtual tests. Bench racing. The add on pack must raise the lead acid SOC from 50 to 85% while simultaneously supplying an additional 1 amp load (carbon pile) @ 24v nominal for a full 4 hours. When the lead and lithium batteries are disconnected at the end of 4 hours, the lead SOC and amount by which lithium voltage exceeds lead is an indicator of how well it did and how much it had left to give(overcapacity). If the voltages are equal and lead SOC is still 85%, the lithium battery exactly met the minimum criteria. If lead SOC is below 85%, the lithium solution failed the test. I may have gone overboard, or chosen unrealistic values, just thought it would be useful to have a standard method for comparisons.


You dont need any of that. And there are no values for lead that will help. And it just makes a simple thing complicated. And while you can do that with lithium to an extent its all but imossible with lead.

If you want to use roughly the same amount of lithium and lead, connect fully charged batteries etc for best range, then add an 8S lifepo4 pack and use a single 100A diode in series with main battery so as to lose around .7 of a volt. And you can then charge the lithium at 3.6Vpc1 (28.8v) and the chair at the chair automatically at the same time at 28.8V - 0.7V = 28.1V. Ideal for gel.

The discharge curves are different. The lead is a long slope. The lithium is an rapid drop, and all day at 3.3xV then a fall right at the end. But as long as you dont let the chair go into the red it will be right and match at both ends, full/discharged.
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Re: how do we charge chair using solar power?

Postby slomobile » 20 Oct 2021, 14:10

shirley_hkg wrote:We are group of 250 wheelchair users , mostly powerchairs.
... we have these (plug in add-ons) , to lend to them.
... The most compact one I've made is
240*110*170h , @24V50Ah. That's more than 1KWH of energy.


Ok, great. That is what I need. What is the group? This forum? or something else?
Can I join? Can I borrow a unit for my camping trip November 5 in Tennessee?
If not, can I get enough detail about the unit to recreate it here?
If the group is UK only, I understand. Would you like to open a US chapter?
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Re: how do we charge chair using solar power?

Postby slomobile » 20 Oct 2021, 14:52



I like the look and durability of the stainless case. Without an earth ground available, how is the case connected electrically? Or is that the function of the attached loop? Dragging a ground strap behind? That might improve the ground plane of my aerial.
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Re: how do we charge chair using solar power?

Postby shirley_hkg » 20 Oct 2021, 15:02

slomobile wrote: What is the group? This forum? or something else?


https://m.facebook.com/directionassociation/
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Re: how do we charge chair using solar power?

Postby Burgerman » 20 Oct 2021, 16:46

I would imagine the case is NOT connected. Hopefully.
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Re: how do we charge chair using solar power?

Postby slomobile » 21 Oct 2021, 23:14

Burgerman wrote:Explain the chair. What is its battery. What is the 2nd battery.

Then explain your plan. And why. Forget about volts and tech stuff just your working principle and why.


The plan is still coming together, learning, adding functions, but this is it so far. If I can't get it together by the Nov 5th camping trip, I'll just keep the old quantum chair on a trailer for standby. A very large reason for this is for me to learn how the stuff works. The function is almost a bonus.

Chair is a used (barely) Permobil M3 made in January 2020. Had 30 miles when I got it in July. 100 now. My miles have been off road grass hills and over weight limit. But I have never drained more than 5 bars at a go and it was fully charged when I picked it up, so batteries should be good.

I've added a Raspberry Pi 400, 12v Project Tango Development kit tablet, small WiFi travel router, cell phone, HackRF one, to the left swingaway armrest.
That stuff is currently powered by a small sla 12v charged by a Wilson cigarette lighter cable and onboard 10w Coleman solar panel The small SLA will be eliminated and replaced by the Lithium packs when they are ready.

Original MK Gells M24 SLD G FT Also dated 1/20 12v63Ah C/5 12v74Ah C/20

Add on battery is still in the air. It will probably end up being 4 individual 12v packs for use in several different situations. 12v (19v OC) 50w square grape solar camp solar panel. I would carry 2 12v bricks on the chair. Connected in parallel for the computer. If the chair batteries are getting low, I shut down the computer and reconfigure the bricks in series to prevent being stranded. Looking for your advice whether its better to connect lead and lithium together in possiby mismatched state of charge, or just run one pack or the other.
I'd like the option to charge 2 12v add on packs at a time with an old powerchair xlr charger, while the chair leads get the stock permobil charger. If necessary, a good hobby lithium charger or something else would be fine.
The weirdest use case is with all 4 add on packs in series to power my well pump during a power outage https://thesolarstore.com/grundfos-sqfl ... p-526.html

It probably makes sense to have the 12v bricks in 2 dedicated pairs so they remain balanced with each other and only ever used together, never singly. The 48 volt use case is rare and I can be sure to drain the higher pack to match the lower before joining them.

It will be important to keep wire and connector resistances stable
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Re: how do we charge chair using solar power?

Postby Dan » 22 Oct 2021, 00:15

slomobile wrote:it was fully charged when I picked it up, so batteries should be good.

Unless you disconnect the chairs batteries you really should charge it about once a week even if its not being turned on.
slomobile wrote:I've added a Raspberry Pi 400, 12v Project Tango Development kit tablet, small WiFi travel router, cell phone, HackRF one, to the left swingaway armrest.

All this can be powered by a 24V to USB adapter (like ones used for motorbikes) plugged into your chairs XLR charger port. Or a portable USB power pack.
Your chair can be charged from a car?

You are good at making something reasonably simple into something sounding complicated.
I'm a dude playing a dude disguised as another dude.
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Re: how do we charge chair using solar power?

Postby Burgerman » 22 Oct 2021, 05:36

There are many reasons why what you propose o=is over complicated and very inneficient.

Just connect the lithium correctly to the lead while both are fully charged(only) so you dont get a massive inrush current. Add a single silicone 100A diode and a 60A fuse in series in the lithium connector. A XT90 or Anderson. To lose 0.7V. This matches the charge voltages of batteries and helps prevent you using more lithium than lead. And have a seperate charge connector connected to the lithium. Through THAT connector only, charge BOTH batteries together with any charger you wish at 28.80V and thats perfect for the Lead (it will see a gel safe 28.1 to 28.2V because of the diode). And the lithium will see a perfect 28.8V

When you do this you gain in every way. Both batteries discharge slower. So with the lead you gain more Ah for free (because less peukert effect). And you will damage your lead battery less as it will not end up as discharged on a daily basis which is the key reason they die as you will get more miles per Ah... It also ensures that the gel batteries are not over volted during charge, which also shortens their service life. Which stock mobility batteries chargers always do.

And another gain... Most gel batteries are charged, and charge is ended way too soon - it really takes 16 hours. So they are 99% charged. That means 1% sulfated. Every charge. It takes 16 hours at a lower float voltage to do that last 1%. But when charged with your lithium that battery, simultaniously that lithium battery then holds the holds the lead battery higher than its naturally fully charged voltage (slightly) after you disconnect the charger. That acts as a float charger for the lead. So you win in 4 or 5 ways, longer lead service life, better range than trying to charge a dead battery from a full one (which doesent work anyway unless you run another charger between the two and lose another 15%)

If the chair batteries are getting low, I shut down the computer and reconfigure the bricks in series to prevent being stranded. Looking for your advice whether its better to connect lead and lithium together in possiby mismatched state of charge, or just run one pack or the other.


Never connect two in a mismatched state unless you want to waste a lot of energy and melt wires or blow fuses. And that will not charge your lead much anyway. It will waste a lot of energy trying. You need to add around 120% more what hours to a lead battery to charge it. The rest is wasted with recombination, resistance (heat) and charge efficiency, esp when nearly full. And you also lose out of all the benefits above.
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Re: how do we charge chair using solar power?

Postby slomobile » 22 Oct 2021, 13:04

Thanks BM, that makes sense. It was handy to have it all laid out together now that you have it worked out, rather than hunting through old threads where you and others debate and hash out the details, never sure what the conclusion is.

Unfortunately your method seems to require the Lithium packs connected to the chair in series all the time once the packs are mated. Is that correct?
Several of the features I was after come from your Parallel charge/Series discharge connector. Is there any way to marry these methods?

Range extension is only 1 function I was seeking. It is needed infrequently. I need the computer every day.
Ripple free 12v supply for ham electronics is another.
Ability to add range and/or computer time from 12v car charger.
Flexibility to apply stored energy to 12v or 24v systems.
Charge one pack with stationary solar while I move with the other pack. Swappable.
Some way to pull 1200W @ minimum 30v to run my well pump in emergencies. This need comes up about twice a year. But it really is a need.

The main limiting factor seems to be ensuring equal voltages as the packs are being connected to limit inrush current and inefficient operation. Correct?
Maybe there is a way to "slow" the connection process with an intermediate capacitor and charge resistors? Don't know how. We have a Pi available onboard for cell monitoring and cell history tracking. Perhaps the Pi could connect and disconnect individual cells, one at a time, to provide both output voltage regulation and cell balancing(by choosing which cell is modulated).
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Re: how do we charge chair using solar power?

Postby Burgerman » 22 Oct 2021, 22:51

Unfortunately your method seems to require the Lithium packs connected to the chair in series all the time once the packs are mated. Is that correct?

No. Just that once connected why would you ever want to remove it? Only be sure they are withing a couple of tenths of a volt and then no big currents.

Several of the features I was after come from your Parallel charge/Series discharge connector. Is there any way to marry these methods?

I dont understand the question.

Range extension is only 1 function I was seeking. It is needed infrequently. I need the computer every day.
Ripple free 12v supply for ham electronics is another.

With lead/lithium connected, a decent quality voltage inverter, to provide a clean 12V will run as long as you want. You will have your 70Ah lead + lithium Ah to go at. And all with reduced peukert, so win win.
Ability to add range and/or computer time from 12v car charger.

I use the PL8 (substitute another hobby charger) to do that. run it from your 12V supply and charge at 28.8V. It can also do a MUCH more sophisticated charge on the lithium pack at the same time and balance all cells, throttle charge rate, etc and terminate charge at the correct time too. .

Flexibility to apply stored energy to 12v or 24v systems.

Hobby charger...


The main limiting factor seems to be ensuring equal voltages as the packs are being connected to limit inrush current and inefficient operation. Correct?

Yes.
Maybe there is a way to "slow" the connection process with an intermediate capacitor and charge resistors? Don't know how.

If you connect a 26v charged lithium pack to a discharged lead battery hundreds of amps will flow for maybe 10 mins or more. I cant waitto see the size of your resistors/capacitors.
We have a Pi available onboard for cell monitoring and cell history tracking.

Whoosh...
Perhaps the Pi could connect and disconnect individual cells, one at a time, to provide both output voltage regulation and cell balancing(by choosing which cell is modulated).

They are all in series with charge current going through. How can you disconnect a cell without all cells stopping charge. And the charger seeing open circuit? Same problem a BMS has. So it instead puts a resistance across the cells that reach the full point to try and discharge them a little in a futile attempt to hold the voltage down to this 3.60V point. While the charger is merrily charging away at say 10A. So that obviously fails. Then the BMS goes in to panic mode. Which it calls overvoltage disconnect. So your cell sees around 3.8 to more volts, then the BMS chops off the charger while trying to get its miserable 100mA resistive load to pull down that cell. As long as the charger hasnt decided that it shoud turn off since it cant "see" a battery, (some do) then it will keep doing this over and over untill the charger thinks its finished. Or the cells get balanced. Thats why I use a hobby charger instead because it never lets a cell go above the safe limit, and it throttles the charge rate instead.
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Re: how do we charge chair using solar power?

Postby slomobile » 23 Oct 2021, 23:23

Perhaps the Pi could connect and disconnect individual cells, one at a time, to provide both output voltage regulation and cell balancing(by choosing which cell is modulated).

They are all in series with charge current going through. How can you disconnect a cell without all cells stopping charge. And the charger seeing open circuit? Same problem a BMS has. So it instead puts a resistance across the cells that reach the full point to try and discharge them a little in a futile attempt to hold the voltage down to this 3.60V point. While the charger is merrily charging away at say 10A. So that obviously fails. Then the BMS goes in to panic mode. Which it calls overvoltage disconnect. So your cell sees around 3.8 to more volts, then the BMS chops off the charger while trying to get its miserable 100mA resistive load to pull down that cell. As long as the charger hasnt decided that it shoud turn off since it cant "see" a battery, (some do) then it will keep doing this over and over untill the charger thinks its finished. Or the cells get balanced. Thats why I use a hobby charger instead because it never lets a cell go above the safe limit, and it throttles the charge rate instead.

I guess I haven't talked about that project publicly much, it is for an experimental towable offroad chair that uses AC induction motors and a ball coupler built in to the front. The concept is still unproven. Doesn't really fit this thread,
Motor controllers are integrated with battery management. Instead of a dedicated series/parallel cell arrangement, each cell has a voltage monitor and FETs at each end so they can be dynamically rearranged (in lieu of PWM, at similar switch rates) into recharging groups, left drive groups, right drive groups, and isolated cells. Individual cells are replaceable. Unbalanced storage is possible because each cell is automatically isolated when switched off. Dynamic balancing is accomplished by leaving a cell in a drive group for more or less time till voltage parity is reached. At any time while in operation at least 1 cell is isolated. As soon as that cell becomes the highest cell, it is rotated into a drive group and the lowest is rotated out. But the assembly is huge, using lots of unobtanium silicon right now. Being large does have the advantage of a large heat spreading area. It is needed, because all those extra FETs with Rds between cells waste more energy than the BMS they replace. Its a learning experience.
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Re: how do we charge chair using solar power?

Postby slomobile » 24 Oct 2021, 00:12

[YouTube]https://youtu.be/tAuPfgZgXec[/YouTube]
Boat user discusses combining Lead and LiFePo4. Explanation was easier for me to follow. Any objections to his explanation?
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Re: how do we charge chair using solar power?

Postby Burgerman » 24 Oct 2021, 06:04

Some of his claims are correct.

Claims lithium is more expensive that lead. - I would say Ah per Ah its the opposite. Maybe its an old video.

Claims best to charge lead at 14V, which is OK on Gel, will severely shorten cyclic life on AGMs esp so on good ones like odyssey. And in the video link at the end of this he is using AGM. So clueless about lead charging. Which need at least a bare minimum of 14.4 and preferably 14.7V or you get litherally 1/3rd of possible service life.

Now claims his "fully charged lead" which he charges "to" 14V (not at) and then stops? Instead of FULLY charging until 1000thC or at least 8 hours at this 14V CV level. Then he says it drops to 12.8V if they are good, and are healthy. Well thats because they are undercharged... They should drop to around 12.95 to 13.15V gel, or at least 12.95V AGM.

He claims the lead battery voltage comes from the two alloys of lead. And theres only one alloy of lead in each battery... And in some batteries no alloy at all. Those use 99.99% or better pure virgin lead. So thats nonsense! In a lead battery both plates are just lead! One coated in lead dioxide. And when discharged the other gets coated in lead sufate from the sulfuric acid in the electrolyte.

Correct about float charge and long life - but only needed if not already propery charged to 100% in cyclic use. Helps in long term storage in cases like on his boats by light loads never needing the lead at all. And so battery sits on a 13.2V float. Should last 15 years.

Claims with lithium, you have to have a Battery Murdering System! Strange how non of ours do (for extremely good reasons) and at least 3 of my lithium packs are a decade old and measure internal resistance and Ah as new...

Says he charges his BMS equiped dumb brick lithiums at 14V. Which means that some cells are likely at 3.6 to 3.65 volts and some are at less than full depending in what BMS in inside, how its programmed and he doesent know.

Says lithium drops to 13.2V. And so float charges the lead. Because his under-charged lead batteries need it. Because his drop to 12.8 right? Well that happens to a battery charged with a useless mobility charger too. And thats what I already explained previously. That lithium you permanantly connect means that the lithium float charges your lead. To make up for stopping the charge too soon. See above... But we dont need this because we CAN properly charge the lead because a) we know better, and b) we are not using this as a backup system for power on a boat. We are using it in a cyclic way. Daily. So by adding a 0.7V drop via a large silicone diode we can charge the lithium FULLY and still charge the lead simultaniously, at the 28.80V (14.4V) we should. Although most lead brick replacements say 14.7V. And use both lithium and lead all day together. Gaining range and better matching the Ah used from each battery.

Once he got to popeye I almost gave up not because he is wrong. He is talking about power systems on a boat. It doesent make much sense to a cyclic user. We use short bursts of high current. And so your addon on pack better be capable of this. High C rates. If used without a diode especially. As it will need to provide all the high power intermittently. And he is going on about how many amps it takes to hold the lead at 13.2V. Well if its more than 100th C (a few milliamps) then the battery isnt properly charged! Hes gone from some accurate info, to off in the realms of his fantasy. He is talking about "waste" power from float... If he charged his lead properly this would be insignificant level as his measured float level (current) is really charging his lead. And that current will fall over time. From days to weeks..

Then he is saying to connect together with large resistor first. Also not needed. If voltages are within a couple of tenths of a volt, the cables and connectors and battery internal resistances ensure no huge currents flow. Many here have built addons. Non of us ever used resistors or had a problem.

Also he is making out like this is something new. Shirley on here was talking to me about this 13 years ago! And he was already doing this back then.

So some of it is right. Some is missing. (Such as what happens at the bottom end when disharged deeply in cyclic use). And some is wrong.


On here he talks about charging. He has not got a clue about lead.
https://www.youtube.com/watch?v=XAOhT2HwKWM
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