Wiring a BMS into a Battery Pack

stoneshirt

Joined Jan 19, 2022
5
Hello, Electron people..
I have built a shallow Water Diving Hookah,powered by a 12v 8amp 100 watt Air Compressor.I am putting together a Lith-on Battery Pack.I have just learned about the importance of a BMS to manage charge,and dis-charge.I'm using 6 18650 Batts in parellel for 7.8 Amps.The Motor is a 8 ampH,so that would give me close to ONE HOUR dive Time,correct? I sourced these Batts from TWO Bauker Power Drills.(new)..Each Pack has a Larger Circuit Board built in,and a SMALLER Board on the END,which I THINK should be a BMS... The BMS is "Battery Minding System"?..Is that the small Circuit Board on the End?..Three Red Wires,One going to V+...Middle One is V- and the One on the right is CH+. to the bigger Board..I would need a Drawing where these should go.I'm very stupid when it comes to Elec Circuits.Can you use your favorite color Crayon and sketch something up? Thanks....stoneshirt

Tonyr1084

Joined Sep 24, 2015
6,863
Welcome to AAC.
I'm very stupid when it comes to Elec Circuits.
NO YOU'RE NOT! Nobody here knows everything. Especially me. You're just embarking on a journey of learning about electronics. We all - according to your words - were "Stupid" at one point.

Without knowing more about this - and its original intended use - I think the two black circled parts of the BMS (Battery Management System) is what you hook the battery to.

I must caution you - - - if this board is from a different chemistry battery or from a different battery voltage - DO NOT TRY TO USE IT! It was designed for a specific battery type and voltage. If the battery you are using and voltage is the same then it's probably safe to connect the battery positive to the upper circle, the pad marked "B+" and "B1" should be connected to the battery negative terminal. I'm not seeing all of the board so I can't tell if there's a temperature sensing component that should be monitoring the battery voltage - another CRUCIAL part of proper circuitry.

Irving

Joined Jan 30, 2016
2,526
I have a feeling you are somewhat confused. If the pump is 12v 8A you must be using 3 18650 cells in series to give 11.1 - 12.6v and then multiple sets in parallel to give the required amperage. If you are using all 6 in parallel you'll only have 3.7v

The small board is just an LED indicator showing 'on charge' and battery level. A proper Battery Management System (BMS) would ensure each cell is properly managed, and the pack balanced, during the charge cycle; if it is then there will be B+, B1, B2, B- terminals to balance the cells.

This 'charger' board will not charge an 8A pack very quickly as its designed to charge a single string of cells over several hours; this is bourne out by only having a B+ and B1 terminal for the battery - it is neither a fast charger nor a full BMS - it will only manage discharge cut-off at around 9v and possibly overcharge cut-off at approx 13v.

@Tonyr1084 The temperature monitor is a 10k NTC thermistor connected at NTC1 just above the red wires on the main board. It looks like its been cut off.

stoneshirt

Joined Jan 19, 2022
5
I have a feeling you are somewhat confused. If the pump is 12v 8A you must be using 3 18650 cells in series to give 11.1 - 12.6v and then multiple sets in parallel to give the required amperage. If you are using all 6 in parallel you'll only have 3.7v

The small board is just an LED indicator showing 'on charge' and battery level. A proper Battery Management System (BMS) would ensure each cell is properly managed, and the pack balanced, during the charge cycle; if it is then there will be B+, B1, B2, B- terminals to balance the cells.

This 'charger' board will not charge an 8A pack very quickly as its designed to charge a single string of cells over several hours; this is bourne out by only having a B+ and B1 terminal for the battery - it is neither a fast charger nor a full BMS - it will only manage discharge cut-off at around 9v and possibly overcharge cut-off at approx 13v.

@Tonyr1084 The temperature monitor is a 10k NTC thermistor connected at NTC1 just above the red wires on the main board. It looks like its been cut off.
Hey.You guys are smooth.Thanks,and give me a Day to absorb this.And I'll come back ...OK?

Irving

Joined Jan 30, 2016
2,526
The Motor is a 8 ampH,so that would give me close to ONE HOUR dive Time,correct?
No, the 6 cells in parallel, ignoring the voltage issue, giving 7.8A implies they are 1300mAH cells. But that is at the 20hour discharge rate, i.e 65mA for 20h. At 1.3A continuous you'll be lucky to get 40 minutes and that's taking them down to near 100% discharge which will severely shorten their life (assuming your 'BMS' will let you discharge them that far). For an hours operation at the marked battery capacity you need a total capacity at least 3 - 4x to give a safety margin.

I'm a little concerned that this appears to be an air supply for a diver? None of this is certified for life-support purposes and it sounds very risky to me. 100w compressor suggests something you pump a tyre up with... if so, it's probably got a duty cycle rating of 10min run, 20min cool down - it almost certainly won't be safe to run continuously for an hour!

stoneshirt

Joined Jan 19, 2022
5
No, the 6 cells in parallel, ignoring the voltage issue, giving 7.8A implies they are 1300mAH cells. But that is at the 20hour discharge rate, i.e 65mA for 20h. At 1.3A continuous you'll be lucky to get 40 minutes and that's taking them down to near 100% discharge which will severely shorten their life (assuming your 'BMS' will let you discharge them that far). For an hours operation at the marked battery capacity you need a total capacity at least 3 - 4x to give a safety margin.

I'm a little concerned that this appears to be an air supply for a diver? None of this is certified for life-support purposes and it sounds very risky to me. 100w compressor suggests something you pump a tyre up with... if so, it's probably got a duty cycle rating of 10min run, 20min cool down - it almost certainly won't be safe to run continuously for an hour!
Hi.Thanks for that.This stuff is overwhelming.I see I was wrong in thinking that 6 of these Batts in Parallel would give me my 12v AND the 7.8ampH.This seems like I will need a ton more of these Batts.Maybe I'll just stick with the 12v 8AmpH Lead Acid Batt that I built into the Proto-type.I need it light as posseble to carry it to the Beach.Irving,these Hookahs are in wide use.We/they use an Air Compressor (Oil-less, Diaphragm) that are used for Aquatic Systems.No duty cycle..(that I know of.) In my use,it will be intermittent.Just going down(6Ft) to retrieve a Target buried in the Sand.The PVC Float acts as a Reserve for Air.

Tonyr1084

Joined Sep 24, 2015
6,863
Six feet eh? I've seen people drown in as little as six inches. All it takes is one gasp of water in the lungs and the diver will be coughing uncontrollably and likely filling his lungs with even more water. I'm no diver but I think I'd prefer the air tank on my back.

Six feet? The beach? Waves? Boats? Long hoses? Takes a hearty individual to place his life dependency on what seems like a sketchy system. Many may be in use; but so are cars. And lots of people die in car accidents all the time. I'll hold my breath for six feet.

Irving

Joined Jan 30, 2016
2,526
Maybe I'll just stick with the 12v 8AmpH Lead Acid Batt that I built into the Proto-type.
Well that won't give you an hour either - it too is spec'd at the 20h rate - and it'll run for even less time than the Li-ion cells because of the higher internal resistance and something called the Peukert effect.

How 'intermittent' is the pump usage?

stoneshirt

Joined Jan 19, 2022
5
Six feet eh? I've seen people drown in as little as six inches. All it takes is one gasp of water in the lungs and the diver will be coughing uncontrollably and likely filling his lungs with even more water. I'm no diver but I think I'd prefer the air tank on my back.

Six feet? The beach? Waves? Boats? Long hoses? Takes a hearty individual to place his life dependency on what seems like a sketchy system. Many may be in use; but so are cars. And lots of people die in car accidents all the time. I'll hold my breath for six feet.
Well I see you aren't inclined to walk the Razors Edge.

Tonyr1084

Joined Sep 24, 2015
6,863
Well I see you aren't inclined to walk the Razors Edge.
Not at my age. I'm not even inclined to walk some of the sidewalks around here.

stoneshirt

Joined Jan 19, 2022
5
Well that won't give you an hour either - it too is spec'd at the 20h rate - and it'll run for even less time than the Li-ion cells because of the higher internal resistance and something called the Peukert effect.

How 'intermittent' is the pump usage?
Hi.The Pump is barely adequate,and doesn't have the Volume/pressure to operate the Regulator/Mouthpiece properly.So I'm going to run it at what they call "Free Flow."..The inhale is not activating the internal Diaphragm,just flowing continuously.That way there isn't much of a load put on the Pump.I search with the detector,Chest deep.,and when I get a Target I will switch on the Pump,and spend a few Minutes on the Bottom,digging.....There's One Hookah that's popular,that has a "Smart Regulator that senses when you inhale,and turns the Pump on Momentarily,for each Breath.But that Pump CYCLES ALOT during it's Life.It' called the Blu-Nemo,and goes for around $1,000.00.I built mine for around$350.00.

Whats the deal on wiring up that Batt Pac with Parallel AND Series..I see they do that.Would that give me what I need?
stoneshirt.

Irving

Joined Jan 30, 2016
2,526
Hmmm, I think I'm with Tony on this one. Apart from the fact the documentation says its expressly not for life-support, that pump claims 150l/min at a pressure of 120kPa. At 6ft depth you need 206kPa of pressure to fill your lungs against the pressure of the water, so you're already marginal. But hey, its your life.

BTW if your lead-acid battery is a typical Chinese one you'll get around 20min of actual run time from it. 18 (3S6P) Cheap Li-ion 18650 cells @ 1300mAH will actually give you 44min.

This 12v 21Ah LiFEPO4 pack will give you 120min and has the added advantage of being safe and won't explode in flames if damaged. It weighs 1.9kg, about 5% less than your current lead-acid battery and is about 20% smaller.

debe

Joined Sep 21, 2010
1,290
You guys have no idea what the OP is using as i use a simmilar setup to 10ft but use a 50Ah AGM battery that gives hours of con tinous dive time. This is used for scrubbing the bottom of a boat or untangling rope from prop shaft.

debe

Joined Sep 21, 2010
1,290
If you are going to use a lead acid AGM battery & pull 8Amps for an hour, you will need at least 20Ah battery. Or buy a 15 Ah lithium battery pack (they are a lot more expensive than AGM but mutch lighter).

Irving

Joined Jan 30, 2016
2,526
You guys have no idea what the OP is using as i use a simmilar setup to 10ft but use a 50Ah AGM battery that gives hours of con tinous dive time. This is used for scrubbing the bottom of a boat or untangling rope from prop shaft.
On the contrary, I have a pretty good idea.

At least you have a decent pressure - 24PSI is 168kPa which is much better than 120kPa and as you say gives you some margin. And a 50Ah AGM will easily give you 4 hours of runtime with a 100W pump, but I guess you're not floating it on a raft, so the 8kg or so weight isn't an issue.

And you just reiterated what I said above...

debe

Joined Sep 21, 2010
1,290
This is how its used if away from the boat. Grandson using it in about 8ft of water. With Granmar keeping an eye on him.

Irving

Joined Jan 30, 2016
2,526
This is how its used if away from the boat. Grandson using it in about 8ft of water. With Granmar keeping an eye on him.
That's neat. Much prefer the rigid flotation arrangement rather than the baby inflatable! Weight can sit down inside making it stable rather than on top and unstable. Do you have a trolley to get it to the beach, 'cos that must weigh around 30lb?

debe

Joined Sep 21, 2010
1,290
Never weighed it as its too easy to carry & fits easy in to the boot of a small car.

debe

Joined Sep 21, 2010
1,290
The Lithium battery Irving posted @ 20Ah 12V looks good to go with.