# Can you Charge a 60 or 72V Battery Pack with "a" 12V Solar Panel?

#### cheez

##### 100 mW
I am planning on building a Li-ion (cylindrical cells) 21700 battery pack for a 60V system for my future e-scooter.
And I live off-grid. Can you use a 12V or 24V solar panel to charge a 60V or 72V battery pack? I thought you have to have a solar panel (or solar panel"s") that has 72V output in order to charge a 72V battery pack.. The battery cell is 3.6V nominal, 4.2V max.

And charge time does not matter to me as I don't mind charging for a few days without using the battery. Anyone?

I have a bad feeling that the 12V solar panel will not be able to charge a 60V or 72V battery pack...
So even with charge controller it wouldn't work because the source (panel) doesn't even have enough voltage to provide to begin with. I don't think the voltage adds up like a building block.. you'd have to have same voltage on the panel as the battery pack. I don't want to hook up six 12V panels in series... it would take up entire roof of my shed. And way too expensive to do it.

As sadhak said, all you need is to find the right charge controller / MPPT / etc.

You need one that takes as input whatever your panel outputs, and then outputs whatever your battery requires, while also performing the current limiting that a battery charger appropriate to your battery pack would perform.

If you cannot find one with the current limiting necessary to emulate a charger, you would have to use one that has appropriate output (inverter, etc) to power an actual battery charger (presumably AC-powered), to prevent damage to your batteries.

If you cannot find one that will accept your single panel's input, you might have to have a second panel in series with it for a high enough voltage to run an appropriate charge controller.

Additionally, a "72v" battery pack needs quite a bit more voltage to fully charge than just 72v--they are typically 20s, which is 84v fully charged to 4.2v/cell.

Now that you know what kind of thing to look for, and what it has to do, it shouldn't be too hard to do your project.

cheez said:
I am planning on building a Li-ion (cylindrical cells) 21700 battery pack for a 60V system for my future e-scooter.
And I live off-grid. Can you use a 12V or 24V solar panel to charge a 60V or 72V battery pack? I thought you have to have a solar panel (or solar panel"s") that has 72V output in order to charge a 72V battery pack.. The battery cell is 3.6V nominal, 4.2V max.

And charge time does not matter to me as I don't mind charging for a few days without using the battery. Anyone?

cheez said:
I have a bad feeling that the 12V solar panel will not be able to charge a 60V or 72V battery pack...
So even with charge controller it wouldn't work because the source (panel) doesn't even have enough voltage to provide to begin with. I don't think the voltage adds up like a building block.. you'd have to have same voltage on the panel as the battery pack. I don't want to hook up six 12V panels in series... it would take up entire roof of my shed. And way too expensive to do it.

Thank you sadhak. I looked at the link to a MPPT controller you provided and re-read your comment. I will look into this controller deeper.

amberwolf said:
As sadhak said, all you need is to find the right charge controller / MPPT / etc.

You need one that takes as input whatever your panel outputs, and then outputs whatever your battery requires, while also performing the current limiting that a battery charger appropriate to your battery pack would perform.

If you cannot find one with the current limiting necessary to emulate a charger, you would have to use one that has appropriate output (inverter, etc) to power an actual battery charger (presumably AC-powered), to prevent damage to your batteries.

If you cannot find one that will accept your single panel's input, you might have to have a second panel in series with it for a high enough voltage to run an appropriate charge controller.

Additionally, a "72v" battery pack needs quite a bit more voltage to fully charge than just 72v--they are typically 20s, which is 84v fully charged to 4.2v/cell.

Now that you know what kind of thing to look for, and what it has to do, it shouldn't be too hard to do your project.
Thanks amberwolf. I will be running 60V system on the scooter (17s, 61.2V nominal, 71.4V max).

Does this mean that the battery charger (shown in pic above) will require 110V (similar to voltage from electrical outlet of a home) for the charger to run?
I won't be using the battery charger. I will be running wires directly from the solar panel charger controller to the scooter battery charging port. The battery pack I will be building can handle up to 5A on charging. The other battery pack will be around 2A.
sadhak and amberwolf, would that MPPT controller you posted would work for me? I will be using a 12V 100w solar panel..

If so, my understanding is it would take longer to charge my scooter battery. But I have no time restrictions. I won't be using a scooter every day, maybe twice a week, so a long time of charging would not be an issue for me.

cheez said:
Thanks amberwolf. I will be running 60V system on the scooter (17s, 61.2V nominal, 71.4V max).

Does this mean that the battery charger (shown in pic above) will require 110V (similar to voltage from electrical outlet of a home) for the charger to run?
Since it is labelled as 100-220VAC input, it *might* run on DC at something between 60-100VDC on it's input, since many so-marked devices do (but not all). It will probably not be able to support the full current output at the lower input voltage, without overheating, so you may have to adjust it's output current (if it has any way to do this internally; some do, some don't) to match the lower input power available.

At a guess, based on things I've tested out like this with a battery input instead of a wall-AC-outlet input, that would probably be half the current it is built to supply to the battery, so if it was a 1.5A charger before, it would be a 0.7A charger when run on the lower voltage DC input.

Side note: that specific charger, with a 67.2v output, won't fully charge your 71.4v battery. If you have a BMS on it that has a balancing function, it may not perform any balancing unless it is either user-programmable to lower the balance-start setpoint, or already has a low enough setpoint for that.

I won't be using the battery charger. I will be running wires directly from the solar panel charger controller to the scooter battery charging port. The battery pack I will be building can handle up to 5A on charging. The other battery pack will be around 2A.

Then I'd recommend either an MPPT / charge controller that you can change the output current limit on to match the pack you are charging at that time (and make sure you remember to do it each time!), or get one that is only capable of the lowest current a pack could tolerate, so you don't accidentally damage a pack by charging it too fast.

sadhak and amberwolf, would that MPPT controller you posted would work for me? I will be using a 12V 100w solar panel..
I haven't looked up which ones would work for your setup; unfortunately I only have a bit of time each night to help out on the forum, so I drop into as many threads as I can to help as many as possible; it often means I can't give las much detail as I'd like or find specific parts for a system. So I tend to have to work on the principle of "teaching someone to fish" rather than going to LongJohnSilver's for them.

amberwolf said:
Side note: that specific charger, with a 67.2v output, won't fully charge your 71.4v battery. If you have a BMS on it that has a balancing function, it may not perform any balancing unless it is either user-programmable to lower the balance-start setpoint, or already has a low enough setpoint for that.
Thank you amberwolf.
Yeah I would like to charge the battery pack less than full (upto 90%'ish). I would like to avoid full charging, which is why I want to have enough battery cells to cover more than a typical 60V system, for more headroom.

OK, so this morning I ordered the three major items. An MPPT controller that sadhak linked here, a 12V 100W solar panel, and an 48V electric scooter.
400W Boost MPPT for Solar Charging 24V-85V Output

It appears to be a real nice effective componentry. I am amazed it can convert 12-18V from solar panel to a desired higher voltage, 67V for example. Looking at the spec sheet you can "set" the voltage output on the controller where you want it, but you can't set the current output.. It says it will push out the current all that is available from the solar panel, so this will be variable current output.

Here is the 12V 100W solar panel I ordered: https://www.amazon.com/gp/product/B09BQZVNFG/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&th=1
Here is the spec:
• Maximum Power (Pmax) 100±3% W
Open circuit voltage Voc(V) 21.4±3% V
Max.power voltage Vmp(V) 18.15±3% V
Max.power current Imp(A) 5.51±3% A
Short circuit current Isc(A) 6.11±3%
Solar cells Efficiency 21.9%

The battery pack that comes with a 48V scooter is cheap base-level batteries, so it will probably can't take more than 2A to be on the safe side.
The battery pack (60V) I will be building (later in the future) is very mean and tough (very high performance) so it can take a lot of beating on the current.

cheez said:
Here is the 12V 100W solar panel I ordered: https://www.amazon.com/gp/product/B09BQZVNFG/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&th=1
Here is the spec:
• Maximum Power (Pmax) 100±3% W
Open circuit voltage Voc(V) 21.4±3% V
Max.power voltage Vmp(V) 18.15±3% V
Max.power current Imp(A) 5.51±3% A

Short circuit current Isc(A) 6.11±3%
Solar cells Efficiency 21.9%

The highlighted part is what the MPPT (maximum power point tracking)
would try to keep the panel load at, to keep the power output of the panel as close to it's 100w maximum as possible to get the most out of it it can.

So your MPPT has to be able to use that form of input, and it has to have the right output to match the battery you want it to charge (or be user-settable in a range that includes what you want it to charge).

Thanks amberwolf.

Ok so I got the 12V 100W solar panel (single panel) installed on my roof.
Wired them to the MPPT controller I received.
Power came on!.. The INPUT voltage shows 19.8~ 19.9V.

But the scooter will take about a months or less to get here...

Will have to wait till I get the scooter so I can actually test charging. Will be wiring directly to the scooter charging port, bypassing the scooter's charger.

I ran some numbers and looks like this is what I will be getting with the 52V battery pack that comes with the scooter:
Sunny day: 52V @ upto 1.75 A.

With the future battery build 60V system (70V'ish max) I will be getting:
Sunny day: 68V @ upto 0.9 A.

Can't provide more amp than that as that is topped out by the single panel.. But that is good, very good, because I want lower amperage to keep the batteries safe, for longer life.

I will let you guys know once I get the scooter.

Cheez posts consistently dangerously incorrect information and advice that could lead to fire and death (in regards to batteries, etc).

Other information is simply incorrect and could lead to wasted money and severe dissatisfaction.

Do not follow any of their advice or information.

Original complete post below:
____________________

Ok guys, I have a good news and bad news.

I got the 12V solar panel to work on charging my scooter that I received using that MPPT controller.
It charges. But at the very very slow rate. It charges at the rate of about 10- 15% of what the panel is rated for (100W).. That is with sunny day, with a few clouds here and there. Most of the time it drops down to 10% or below. Instead of getting expected rate of 1.75A on charging this 54V scooter I was getting 0.15- 0.20A at best.

Even more serious problem was that the scooter battery (brand new scooter) kept losing charge, while charging from the solar panel.. So it was taking for-ever. One time I managed to gain 0.4V after all day of charging but then it started losing charge again and brought back down to where it was before. After a couple days of charging, I ended up losing more voltage after all that charging.

Turned out that it was the BMS in the battery that was interrupting with my solar charging. The BMS was keep draining (discharge) my battery while charging. That is why I was not able to make any progress on charging my scooter.

So I opened up the battery pack and removed the BMS. Re-wired the battery so it connects to the controller and charging port directly.

It is charging now, WITH progress. I am able to keep charging without battery getting drained like it was doing before with the BMS in there.

Turned out that the BMS was constantly discharging my battery during charging. The BMS discharges it at certain voltage rate and my solar panel wasn't providing enough power to overcome that. You don't have this issue (or don't really notice it) with charging from wall electrical outlet in your home because the charging amount is much greater than what the BMS draws.. A lot of waste of electricity if you ask me. What's really bad is for the people that live off-grid living in a shed/cabin. They are going to have serious problems. You would need several 12V panels, at least 4, to win wrestling against the BMS. Even with that it would still take a long time to fully charge your scooter because of the discharging from the BMS. I will make a tutorial on how to remove the BMS from scooter or e-bike batteries so the helpless homeless people can charge theirs with success.

I will be getting a 250W 24V solar panel and add to my existing solar panel on the roof. It will be linked in series, total of 36V. It will be about 3.5 times more power than it is now. Should be able to fully charge my scooter in 1.5 days to 2 days at max. I will let you know with the update. Hope to get the 24V panel soon.. as money becomes available.

cheez said:
Thanks amberwolf.

Ok so I got the 12V 100W solar panel (single panel) installed on my roof.
Wired them to the MPPT controller I received.
Power came on!.. The INPUT voltage shows 19.8~ 19.9V.

But the scooter will take about a months or less to get here...

Will have to wait till I get the scooter so I can actually test charging. Will be wiring directly to the scooter charging port, bypassing the scooter's charger.

I ran some numbers and looks like this is what I will be getting with the 52V battery pack that comes with the scooter:
Sunny day: 52V @ upto 1.75 A.

With the future battery build 60V system (70V'ish max) I will be getting:
Sunny day: 68V @ upto 0.9 A.

Can't provide more amp than that as that is topped out by the single panel.. But that is good, very good, because I want lower amperage to keep the batteries safe, for longer life.

I will let you guys know once I get the scooter.

On your van roof?

Ok, so I received a 24V 200+w panel for an addition to my existing 12V panel. I put connected them in series. The controller came live, reading at the correct combined voltages (45'ish upto 60V).

With the 12V panel in the past I was getting output power of:

54.6V @ anywhere from 0.15A to 0.35A

With the 12V and 24V panels connected in series is giving me:

54.6V @ anywhere from 0.45A to 1.2A. It did go past 1.2A in some instance.

Looks like 3 times or more better in power delivery..

The problem is my Chinese scooter has Chinese battery pack and it loses charge anywhere from 0.5V to 0.8V over each and every night. When I was using just a 12V panel I was getting almost nowhere... Because of this issue I only get about 0.2 to 0.1V of charge a day... Would take me about a month or two to fully charge from 44V to 54.6V.
Now with my 24V panel added I get about 1.2 to 1.3V per day. That is with battery loss of charge taken into account. While charging it does get to about 2V of charge each day.

I want to warn you homeless guys and those that live in off-grid cabin, DON'T buy a 12V panel.... it's only good for charging a little battery pack for your 5V lights and phone. That's it. You would ideally need 2 x 24V panels, anywhere from 400~ 500W rated total. And stay away from buying scooters with Chinese batteries... They lose charge easily on any kind of weather.. My battery lost charge by 0.6V on the first day overnight after I fully charged my scooter at my parents' home using a wall charger. And that was room temperature. When you buy a scooter or e-bike make sure it comes with some quality name brand batteries like Samsung.

Man, going solar panel is much more expensive than I thought... Later I will add another 24V panel that puts out even more power (270W rated). Run 2 x 24V panels for scooter charging. Run the 12V panel separately, to charge a small battery for my lights, fans, etc.

tomjasz said:
On your van roof?
my shed roof. Sorry for the late answer..

Ok I did some more testing and cut down more trees... Turns out that the 24V panel I added is putting out a lot more power than I initially found. It needed more direct sunlight. My solar panel setup (12V panel + 24V panel in series) is giving me jaw dropping 4.2A It was hovering between 4A and 4.2A.. That's twice the power of what a common electrical outlet wall charger provides.. Crap it's so strong I had to stop charging cause my Chinese battery pack can't take that. So I started charging in the morning and in the early evening...

One more thing to add, the charge controller (see pic above posts) continues to charge, past set voltage. For example, if you set the voltage for charging at 54.6V it keeps charging and ended up charging up to almost 60V (59.5V to be exact). This auto-stop charging feature does not work. It appears to rely on the BMS in the battery pack to stop the charging. Since I don't have the BMS in my battery pack it just kept going...The battery cell appears to be around 4.55V to full, not 4.2V. They are 18650 cells.

.

you just throwing mud at the walls to see what sticks?

Nothing is more expensive.

Get high-voltage panels, all exactly the same model, each on its own should be higher than your target output by at least 10V

Get good quality controllers.

Stop mucking about, if you can't afford to do it properly, hold off and save until you can.

Oh sorry didn't realize this is the cheez thread

Don't mind me carry on

Another option is what I do when boondocking with my van. It has 200 watts of solar on the roof and 150 ah of house battery. I plug my Luna mini-charger into a 500 watt inverter running off the house batteries and charge the 52v packs from there. It pulls a little more than the solar produces on a sunny day but that comes out of the house batteries and is replenished to the house batteries from solar when the ebike charging is done. Yes there are some inefficiencies from the multiple steps up and down in voltage but has worked pretty well for the last couple of years.

john61ct said:
you just throwing mud at the walls to see what sticks?

Nothing is more expensive.

Get high-voltage panels, all exactly the same model, each on its own should be higher than your target output by at least 10V

Get good quality controllers.

Stop mucking about, if you can't afford to do it properly, hold off and save until you can.
I am poor. I don't have money which is why I was asking about if 12V panel would be do-able, but turned out it would take several months (not exaggerating, realistic figure) to make one full charge. I didn't know the fact that the effectiveness in power is only 10- 15% of the Solar rated power.. That is wayyyyyyyyyy different than what the book I read on solar panels suggested. However the 24V panel made a world of difference. Oh you can mix match panels with different voltages also if they are connected in series. The voltages get added up.

.

Charged all summer from 3 12v panels. Put them in series for 36v (more like 54v) with a PPT buck charger. Had two batteries so swapped them out when one was charged. Figure 1-300w panels is all I need. My 3 were only 15w each so it took too long. The charger quit on me, still looking for a better replacement. My charger let me set max charge so never charger over 85%.

ZeroEm said:
Charged all summer from 3 12v panels. Put them in series for 36v (more like 54v) with a PPT buck charger. Had two batteries so swapped them out when one was charged. Figure 1-300w panels is all I need. My 3 were only 15w each so it took too long. The charger quit on me, still looking for a better replacement. My charger let me set max charge so never charger over 85%.
Might be better to go with 24V panels.. Add a 24V panel to your existing 3 x 12V panel setup in series connection. That will make a night and day difference. From my experience I am seeing that the 24V panel is 3~ 4 times more effective than the 12V panel.
My 12V+24V panel setup got me upto 5A current @ 55V!

.

I want to give a long-term review/update on the solar panel with this elejoy 400W Boost MPPT for Solar Charging 24V-85V MPPT controller..

Was able to charge at 60V @ 5A

The problem is that this controller does not allow current adjustment so it is very dangerous for your batteries. I don't recommend this to everyone.. Get a Step-Up (boost) or Step-Down (buck) DC-DC converter or other MPPT/PWM controllers that allow you to adjust the current. I don't recommend this.

.

The MPT 7210A. Mppt controller is a good bet @ \$50 on ebay.
It takes 12-60v input and the output can be set to 24-72v precisely together with the current 0-10A. with a CC/CV charge profile for lithium ….600w max.
It is a DC/DC boost converter so it will also function as a charger from a DC power supply if no solar input is available.

Hillhater said:
The MPT 7210A. Mppt controller is a good bet @ \$50 on ebay.
It takes 12-60v input and the output can be set to 24-72v precisely together with the current 0-10A. with a CC/CV charge profile for lithium ….600w max.
It is a DC/DC boost converter so it will also function as a charger from a DC power supply if no solar input is available.

I have the MOT 7210A but recently moved to the Grin offering.
\$25-\$30 less on Aliexpress. Darn Grin shipping has gotten expensive. Except for goods on Amazon.

Thanks amberwolf.

Ok so I got the 12V 100W solar panel (single panel) installed on my roof.
Wired them to the MPPT controller I received.
Power came on!.. The INPUT voltage shows 19.8~ 19.9V.

But the scooter will take about a months or less to get here...

Will have to wait till I get the scooter so I can actually test charging. Will be wiring directly to the scooter charging port, bypassing the scooter's charger.

I ran some numbers and looks like this is what I will be getting with the 52V battery pack that comes with the scooter:
Sunny day: 52V @ upto 1.75 A.

With the future battery build 60V system (70V'ish max) I will be getting:
Sunny day: 68V @ upto 0.9 A.

Can't provide more amp than that as that is topped out by the single panel.. But that is good, very good, because I want lower amperage to keep the batteries safe, for longer life.

I will let you guys know once I get the scooter.
Out of curiosity, why are you charging it from the panel versus grid source? Is there a particular reason? Just being eco friendly

Does this mean that the battery charger (shown in pic above) will require 110V (similar to voltage from electrical outlet of a home) for the charger to run?
I won't be using the battery charger.
I wouldn't be using that charger either. Call me superstitious but a battery charger called TangsFire with flames logo?

I wouldn't be using that charger either. Call me superstitious but a battery charger called TangsFire with flames logo?
Lol Tang means Offensive in Chinese. Offensive Fire! -I'd be offended

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