Just having fun... (please comment... I'm new to this)

[Supervstech]

Thanks.... yes, i saw those and I have put some values in but I am unsure of them since my battery bank has weird voltage ranges.

Here are the specs
Battery type : Lithium-Ion
Nominal voltage: 3.7 V
Operating voltage range:
Minimum : 3.0V
Maximum : 4.2V
Length: 5.875" (148 mm)
Width: 1" (26 mm)
Height: 4,5"(over terminals) (113 mm)
Mass: 1.65 pounds (0,72 kg)

If I fully charge the batteries I get 16.8 volts which is too high to run 12 volt appliances. My inverter craps out at that voltage.

I think the max I can go is 15 volts to run 12 volt appliances.... right?

Also ... each cel cannot go under 3 volts... so my range of voltage for my bank needs to stay between 12 and 15 volts.

1) What does this mean for the capacity of my battery (my AMP hours)? each cel if rated for 25 AMP hours.
2) What are the input values you recommend on the MP50? (They would be different than the Battle Born for sure)

Any recommendations are welcome... thanks

This is the main reason most shy away from LiIon cells for 12v stuff...
the LFP LiFePO4 just work out so much better. Also, there is no chance of the cells catch fire

 

[erik.calco]

This is the main reason most shy away from LiIon cells for 12v stuff...
the LFP LiFePO4 just work out so much better. Also, there is no chance of the cells catch fire

@Will Prowse always point out that they "boost" the voltage with 3S with the 3.7V cells in the portable units he reviews. I'd like to find a simple tiny circuit that can handle the required current to boost or drop down voltage for 3S and 4S builds, or a BMS that can do it. These batteries are cheaper than LPEs, and thus used a lot more in smaller packs like battery banks.

@Paul.Barrette without anything to lower the voltage, 3S is the more common configuration for 3.7V for a 12V application. You still can't realistically use the full range. but, that is the winner overall. You do, in that configuration, need to be sure you never exceed 12.6V when charging, as 4.2V is a very important upper limit to respect.

 

[Paul.Barrette]

@Will Prowse always point out that they "boost" the voltage with 3S with the 3.7V cells in the portable units he reviews. I'd like to find a simple tiny circuit that can handle the required current to boost or drop down voltage for 3S and 4S builds, or a BMS that can do it. These batteries are cheaper than LPEs, and thus used a lot more in smaller packs like battery banks.

@Paul.Barrette without anything to lower the voltage, 3S is the more common configuration for 3.7V for a 12V application. You still can't realistically use the full range. but, that is the winner overall. You do, in that configuration, need to be sure you never exceed 12.6V when charging, as 4.2V is a very important upper limit to respect.

Hmmm interesting.... I never saw it that way.... 3s makes sence. For whatever reason I always though you needed to go in pairs

 

[eddie1261]

Wow. "Impressed" doesn't quite cover it! Beautiful, clean wiring!

 

[erik.calco]

Hmmm interesting.... I never saw it that way.... 3s makes sence. For whatever reason I always though you needed to go in pairs

The primary limitation to 4S is most inverters cutoff at 16V, and some as low as 15V. 4 x 4.2 = 16.8V.

If you locate anything to drop down voltage let me know. Can't cost a lot as you are generally not spending much on a small pack. But, does have to be able to handle the amps of the application.

This isn't my top priority today, otherwise, I'd be compiling a list. It is on my long list of TODO items. But, if you're researching it, I'll note anything you post on bumping 3S voltage, dropping 4S voltage, or just voltage regulating tools in general.

 

[Paul.Barrette]

@Will Prowse always point out that they "boost" the voltage with 3S with the 3.7V cells in the portable units he reviews. I'd like to find a simple tiny circuit that can handle the required current to boost or drop down voltage for 3S and 4S builds, or a BMS that can do it. These batteries are cheaper than LPEs, and thus used a lot more in smaller packs like battery banks.

@Paul.Barrette without anything to lower the voltage, 3S is the more common configuration for 3.7V for a 12V application. You still can't realistically use the full range. but, that is the winner overall. You do, in that configuration, need to be sure you never exceed 12.6V when charging, as 4.2V is a very important upper limit to respect.

If I have 3S ... I would be charging the battery to 100% pretty much all the time to get to 12.6V
If I go 4S I would be charging the battery to only 85% to get to 14 volts.

Wouldn't I prolong the life of my battery pack by going 4S and using the MT50 configuration to limit the voltage of my pack by stoping the charge once it is at 14 volts?

 

[erik.calco]

If I have 3S ... I would be charging the battery to 100% pretty much all the time to get to 12.6V
If I go 4S I would be charging the battery to only 85% to get to 14 volts.

Wouldnt I prolong the life of my battey pack by going 4S as I am today?

You have to look at the skew between capacity and voltage on the charts. I think Jehu did a video on this and concluded that you obtain higher usable capacity with 3S, which is primarily what matters presuming you can control the cutoffs and charge profile.

 

[JeepHammer]

I'm a homesteader,
Big gardens, home canning & jarring, chickens, deep wells, electric fences, outside lights, etc.

Everyone says, "65 watt panels that are 25-30 years old, those are junk"...
"Batteries that won't pull in a battery bank, those are junk"...

WELL...
A fence charger with battery, those old stray panels on a corner post do just fine,
The old batteries that aren't making the grade in a battery bank do just fine on a fence charger by themselves.

Same with a little LED light in an animal shelter, or a water level warning on a water trough.
I don't want to run my own power grid over 108 acres, but if a float valve goes on a water trough, I want to know my water pump is running and sucking power because a 10¢ gasket failed, I'd rather it turned on a flashing $2 bicycle flashing 'Tail' light...

There is also the question of security,
I know what those electric fences are for.
I went one step further, I replaced the LEDs in those motion sensor lawn/sidewalk lamps (China, $5 each, come with little solar panels, battery, motion sensors, control board).

I replace 'White' light LEDs with IR, use night vision optics on the rifle, when a hog, fox, coyote, stray dog or cat trips the motion sensor, they can't see it, but I can see them...
Same as IR trail/game cameras, but the threat/varmint is removed.

I buy IR LEDs by the 100 or 1,000 ot bags off surplus sites, but those LED IR rings from night vision camera are really cheap, posted out further it really extends the range of my night vision.

White light, older solar panel horizontal make rain shield on top of pipe, battery mounted on pipe, LEDs on cheap yard lamp controller,
Drive a metal fence post, lower the lamp pipe over it and it's mobile, put it where you want for as long as you want.
Light comes on a dark, or motion sensor, and goes off at daylight.

You just found a use for all those little cheap surplus batteries from cordless tools, emergency exit lights, etc.
Panel small enough, you don't need a charge controller...

-----------

I recognize that old wagon with steering, if it used to be 'Green' it's center tube so it flexes, but it will go places a rigid frame won't.
The first thing I tough was "DEER CAMP!"
We have an issue with vandals, so portable is good, lots of old busses repurposed as 'Deer Camps' around here.

I actually like the home built thing, and you did a good job!

 

[Paul.Barrette]

You have to look at the skew between capacity and voltage on the charts. I think Jehu did a video on this and concluded that you obtain higher usable capacity with 3S, which is primarily what matters presuming you can control the cutoffs and charge profile.

This is the result of the test done by the person I bought the cels from:

 

[erik.calco]

This is the result of the test done by the person I bought the cels from:
View attachment 2609

See how most of the capacity is in the 3.4-4.2 range? It's not linear as you approach the low end, but rather a steep drop in voltage. This is why most do not let these cells go below 3.2V. There just isn't enough capacity below that to make it worth it. 14 / 4 is 3.5V. Your range would be 3.2-3.5V. Line that up with the X on that chart to get an idea how much capacity you'd have in that range. Then do that with 3S.

 

[Paul.Barrette]

See how most of the capacity is in the 3.4-4.2 range? It's not linear as you approach the low end, but rather a steep drop in voltage. This is why most do not let these cells go below 3.2V. There just isn't enough capacity below that to make it worth it. 14 / 4 is 3.5V. Your range would be 3.2-3.5V. Line that up with the X on that chart to get an idea how much capacity you'd have in that range. Then do that with 3S.

Ouch .... that's like 4-5 AH

I was thinking of maybe stepping the battery pack up to 24 volts by adding two other cels and then introducing a voltage converter to go from 18-24 volts down to 12 volts ... this would give me more range to work with

Is this a good strategy with these cels or should I just move on? I can get two more cels for 23$ US each

 

[erik.calco]

Ouch .... that's like 4-5 AH

I was thinking of maybe stepping the battery pack up to 24 volts by adding two other cels and then introducing a voltage converter to go from 18-24 volts down to 12 volts ... this would give me more range to work with

Is this a good strategy with these cels or should I just move on? I can get two more cels for 23$ US each

I don't know the best solution. I just know that 3S is much more common for these for 12V applications for the reason I said.

LiFePO4s are really a lot easier in this regard. 4S for 12V, 8S for 24V. And much safer if you plan on storing in your home for anything other than a portable unit.

What kind of load are you hoping to put on it?

 

[Paul.Barrette]

I don't know the best solution. I just know that 3S is much more common for these for 12V applications for the reason I said.

LiFePO4s are really a lot easier in this regard. 4S for 12V, 8S for 24V. And much safer if you plan on storing in your home for anything other than a portable unit.

What kind of load are you hoping to put on it?

Very low loads... I have to power:
1) 3 lead light 5 minutes a day
2) a small water pump for 60 minutes, once a week
3) My fence energizer 24 /7

I had a Goal Zero 400 lead acid version (sold now because I wanted to do this project) that powered the above no problem. never brought it down to lower than 80%.... used max 8 AH one day a week.

I can get more precise data if needed

 

[SolarRat]

I've been using 3s li-ions for a decade now for my 12v radios, metal detectors, lights etc. I charge to 4.2 per cell and they last a long long time before dropping to 12.2v. I tried undercharged 4s and they didn't have anywhere near the capacity, not enough meat at those voltages. I use fully charged 4s for car jump start packs though.

 

[erik.calco]

Very low loads... I have to power

1) 3 lead light 5 minutes a day
2) a small water pump for 60 minutes, once a week
3) My fence energizer 24 /7

I had a Goal Zero 400 lead acid version (sold now because I wanted to do this project) that powered the above no problem. never brought it down to lower than 80%.... used max 8 AH one day a week.

I can get more precise data if needed

Are these all 12V DC or do you need an inverter to run any of them?

The core question is what voltage range can they handle and how do you stay in that range.

Also, regarding these cells vs LFPs, you really need a balancer for protection for non LFP. I mean, you want it for all chemistries. But, you have to have something to prevent runaway. The basic problem with cells in series is if one cell is failing or not charging enough, without a BMS, the charger does not know. The effect is it tries to overcharge the other cells. This can destroy the good cells, at a minimum. But, there is fire risk with the non-LFPs.

Until you commit to a chemistry and how many in series, you can't really pick a BMS. But, you do want to factor that in, and understand it is more critical with non-LFP chemistries.

But, going back to your loads, you typically start there and work backwards, as they define your minimum requirements, especially if using existing equipment. And voltage range is one of the parameters of your loads.

You then have to ask how you'll get to that voltage range. I really want to look into options for converting. I know you can do 24 to 12v easy. But, we see all the time products that have interesting battery configurations then convert to meet w/e requirements they have. But, no one I've seen has broken down how they are doing it. What chips or circuits are on their boards? What options are available for integrating such a circuit?

What I'd like to do is get a variable one, where I can dial the conversion up or down, and just use that for testing.

Your easiest route for now, though, is to test 3S. If it works for your loads, and you can live with the limited capacity range, then get a 3S BMS for protection, balance them and use the 3 cells that match the most, particularly on internal resistance. Keep the 4th as a spare or use it to power LEDs or USBs. I noticed a lot of the "DIY" power packs they are selling online just take 1S of 18650s of the 3.6V nominal, usually 4-8 in parallel. But, your cells look like they equal a good quantity of 18650s by the weight you listed of 0.72kg. You could hook up one of their circuit boards and charge via USB. The USB boards are yet another example of a voltage regulator built onto the circuit boards to provide stable boosted power.

One plus to the limited capacity range is more cycle life. So, you aren't really losing in the long run. It's more about how much you need in a 24 hour period and how long you can weather cloudy days, and that takes you back to your load requirements, and ability to recharge on a sunny day (PV capacity and charge rate).

I just weighed 10 18650s at 0.5 kg (in 5 plastic cases cuz don't really want to take them out lol) But that puts one of your cells near 15 of these. That extra cell would make a killer USB power bank.



I'm guessing your cells are near 30aH. That's about 110WH per cell, or 330WH for a 3S. Your capacity will be less based on the bottom end of the voltage your load can operate at, and where that falls on the DoD chart you posted. So, if you can achieve 80% capacity, that's 264WH.

 

[erik.calco]

BTW, where are you getting these cells for $23? If they are 30aH, then I like the price for a power pack, because that comes to $1.53 per 2aH 18650, which is unbeatable if you have a quality cell.

 

[Paul.Barrette]

BTW, where are you getting these cells for $23? If they are 30aH, then I like the price for a power pack, because that comes to $1.53 per 2aH 18650, which is unbeatable if you have a quality cell.

They are 25 AH...

I got a deal from a friend but only for my 4 and I can get two more if I want them and I pick them up locally ... no extra shipping. Standard price is 40$ canadian per cel + shipping. Here is the link:

Panasonic prismatic lithium-Ion battery cell 25AH (20.7AH tested) 3.7V (Tesla) | eBay

Find many great new & used options and get the best deals for Panasonic prismatic lithium-Ion battery cell 25AH (20.7AH tested) 3.7V (Tesla) at the best online prices at eBay! Free shipping for many products!

www.ebay.ca

The person I bought them from purchased this pack and sold me a couple of cels:

Module of 21 Panasonic prismatic lithium Ion battery cell 25AH 3 7V Tesla Leaf for sale | eBay

Find great deals on eBay for Module of 21 Panasonic prismatic lithium Ion battery cell 25AH 3 7V Tesla Leaf. Shop with confidence.

www.ebay.ca

 

[Paul.Barrette]

Are these all 12V DC or do you need an inverter to run any of them?

The core question is what voltage range can they handle and how do you stay in that range.

Also, regarding these cells vs LFPs, you really need a balancer for protection for non LFP. I mean, you want it for all chemistries. But, you have to have something to prevent runaway. The basic problem with cells in series is if one cell is failing or not charging enough, without a BMS, the charger does not know. The effect is it tries to overcharge the other cells. This can destroy the good cells, at a minimum. But, there is fire risk with the non-LFPs.

Until you commit to a chemistry and how many in series, you can't really pick a BMS. But, you do want to factor that in, and understand it is more critical with non-LFP chemistries.

But, going back to your loads, you typically start there and work backwards, as they define your minimum requirements, especially if using existing equipment. And voltage range is one of the parameters of your loads.

You then have to ask how you'll get to that voltage range. I really want to look into options for converting. I know you can do 24 to 12v easy. But, we see all the time products that have interesting battery configurations then convert to meet w/e requirements they have. But, no one I've seen has broken down how they are doing it. What chips or circuits are on their boards? What options are available for integrating such a circuit?

What I'd like to do is get a variable one, where I can dial the conversion up or down, and just use that for testing.

Your easiest route for now, though, is to test 3S. If it works for your loads, and you can live with the limited capacity range, then get a 3S BMS for protection, balance them and use the 3 cells that match the most, particularly on internal resistance. Keep the 4th as a spare or use it to power LEDs or USBs. I noticed a lot of the "DIY" power packs they are selling online just take 1S of 18650s of the 3.6V nominal, usually 4-8 in parallel. But, your cells look like they equal a good quantity of 18650s by the weight you listed of 0.72kg. You could hook up one of their circuit boards and charge via USB. The USB boards are yet another example of a voltage regulator built onto the circuit boards to provide stable boosted power.

One plus to the limited capacity range is more cycle life. So, you aren't really losing in the long run. It's more about how much you need in a 24 hour period and how long you can weather cloudy days, and that takes you back to your load requirements, and ability to recharge on a sunny day (PV capacity and charge rate).

I just weighed 10 18650s at 0.5 kg (in 5 plastic cases cuz don't really want to take them out lol) But that puts one of your cells near 15 of these. That extra cell would make a killer USB power bank.

View attachment 2613

I'm guessing your cells are near 30aH. That's about 110WH per cell, or 330WH for a 3S. Your capacity will be less based on the bottom end of the voltage your load can operate at, and where that falls on the DoD chart you posted. So, if you can achieve 80% capacity, that's 264WH.

(They are rated at 25 AH)

Wow .. this is great information .... my brain will explode soon (like my batteries)... too much information to process.
I will definitely go the 3s route and I already have a BMS. I have a small inverter but it is not required ... I can live without it and that is the item that craps out at low and high voltage... I'll check the other items for voltage requirements

For the extra cel... What would I use to charge just one of my 4.2 volt cels? What would I use to step up the voltage to 5 volts? I will search online... any suggestions welcome

 

[erik.calco]

(They are rated at 25 AH)

Wow .. this is great information .... my brain will explode soon (like my batteries)... too much information to process.
I will definitely go the 3s route and I already have a BMS. I have a small inverter but it is not required ... I can live without it and that is the item that craps out at low and high voltage... I'll check the other items for voltage requirements

For the extra cel... What would I use to charge just one of my 4.2 volt cels? What would I use to step up the voltage to 5 volts? I will search online... any suggestions welcome

I'll look when I have a chance. But, they sell these "DIY" power packs where you just add 18650 cells. Why I quote "DIY". How is just adding batteries DIY? But that's what they call it on the ebay listings.

I remember seeing that you could also buy the circuit board w/o the case, which is what you'd want. It does it all. Has USB in and out, so you can charge with USB and then plug USB devices into it, to charge a phone, for instance. But that board obviously has a voltage regulator for 3.6V to 5.1V.

BTW, I jump back and forth between 3.6V and 3.7V. They are both the same cells. 3.6V is technically correct, but marketing rounded it up to 3.7V, so that's what we see everywhere. Marketing always wins over technical, so one day, 3.6V nominal will probably disappear completely.

 

[Paul.Barrette]

I'll look when I have a chance. But, they sell these "DIY" power packs where you just add 18650 cells. Why I quote "DIY". How is just adding batteries DIY? But that's what they call it on the ebay listings.

I remember seeing that you could also buy the circuit board w/o the case, which is what you'd want. It does it all. Has USB in and out, so you can charge with USB and then plug USB devices into it, to charge a phone, for instance. But that board obviously has a voltage regulator for 3.6V to 5.1V.

BTW, I jump back and forth between 3.6V and 3.7V. They are both the same cells. 3.6V is technically correct, but marketing rounded it up to 3.7V, so that's what we see everywhere. Marketing always wins over technical, so one day, 3.6V nominal will probably disappear completely.

Is this what you are referencing...

Adafruit PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C [ADA2465] : Amazon.ca: Electronics

Adafruit PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C [ADA2465] : Amazon.ca: Electronics

www.amazon.ca