Can anyone recommend a reasonable/quality BMS + voltage regulator that I can use to create a 3S 18650 cell battery please?

Hi @pixel8,

   Before getting too involved with BMS recommendations, which I'll leave to others, have you verified that the battery you are considering will power the unit for a suitably long enough period between charges?

Please note, I am not saying this is a problem, just that the limited information I can see, leaves a question in my mind.

The power adapter spec you quote, and confirmed on the website you mentioned, can supply 9V at 600mA. Now, I would expect the current demand by the camera to be less than this supply can provide, but for a quick 'back of an envelope' style calculation, let's assume the camera continuously consumes 600mA.

Assuming your battery consists of three 18650 cells in series, as you discuss.

A fairly good 18650 cell might be specified to be 2400 mAH ... so when connected to a 600mA load, it will be completely drained in 2400/600 = 4 hours.

Obviously, this current demand is overly pessimistic, but it illustrates that unless the camera is only used for short periods of a time, rather than continuously, then the current demand must be kept low for a reasonable 18650 battery life between charges. For example, 10mA might provide 7-10 days (240 hours) operation between charges.

Hence, I would respectfully suggest you start by determining the actual current consumption of the camera - I had a quick glance at the web site you quoted, but didn't see a value specified.

And personally, as a cautious cynic, if the first estimate looked favourable, then I would do a simple test to double-check the actual running time, with a set of cells freshly charged in simple standalone charger.

Also remember, an almost fully charged cell, may have a terminal voltage of around 4.2V, so that 3 cells in series will be around 12.6V. You may need a regulator to avoid damaging the camera, if the camera is only specified to accept 9V.

I hope your project goes well, and apologies for wasting your time, if you have already covered this possible issue.

Best wishes, Dave

@davee @pixels

But if it's a 3 cell pack, wouldn't he be (theoretically) drawing the same current from eeach. That's make the cell pack last 12 hours.

Hi @will,

   Brits of certain age may remember a pair of TV comedy series 'Yes, Minister' and 'Yes, Prime Minister', in which the Minister 'Jim Hacker' was in continual competition with his chief advising civil servant 'Sir Humphrey'. A recurrent theme being Hacker would ask a pertinent question, expecting agreement, and Humphrey would initially 'agree' with a 'Yes' and then qualifying it with some downsides, making the overall result a 'disagreeing' 'No'.

 Similarly, my answer will also be : Yes .... and No!   Though not for any political reason!

   wouldn't he be (theoretically) drawing the same current from each?   ... YES

  That's make the cell pack last 12 hours. ... NO

  ----------------

For simplicity, assume each cell has a terminal voltage of 3V, and is passing 600mA current.

  For a power flow equivalent to 9V 600mA. Which is 9(V) * 0.6 (A) = 5.4 Watts

  Each cell would be providing 3V 600mA ... Which is 3(V) * 0.6 (A) = 1.8 Watts

Because the cells are in series, the total battery voltage is 9V, and it is supplying 5.4 Watts, with a current of 600 mA.

Hence, each (2400mA) cell will completely discharge at the same rate as if it was individually connected to a load drawing 600mA, when supplied with 3V potential from that single cell.

....

For a rough (and mechanically dubious) analogy, assume starting with a water pump that pumps 6 litres per second, with a pressure of 10 bar.

Now connect three such pumps in series, so that the output of the first is the input of the second etc.

Then, assuming the pumps behave like the cells, the water flow is still 6 litres per second, but the pressure at the output of the third pump is 30 bar.

If the water source is a single tank of 2400 litres, then it will be emptied in 400 seconds, regardless of whether there is one pump or three pumps in series, but the pressure of the water from three pumps is three times that of the single pump.

---

Does that help?

Best wishes. Dave

Posted by: @davee

↑

Hi @will,

   Brits of certain age may remember a pair of TV comedy series 'Yes, Minister' and 'Yes, Prime Minister', in which the Minister 'Jim Hacker' was in continual competition with his chief advising civil servant 'Sir Humphrey'. A recurrent theme being Hacker would ask a pertinent question, expecting agreement, and Humphrey would initially 'agree' with a 'Yes' and then qualifying it with some downsides, making the overall result a 'disagreeing' 'No'.

I loved both series, my favourite character was the Secretary Bernard.

Posted by: @davee

↑

Does that help?

Yes, thanks

Posted by: @pixel8

↑

I need to power a https://www.pbtech.co.nz/product/CCTTPL1312/TP-Link-Tapo-C310-3MP2K-Outdoor-Home-Security-Wi-F&source=gmail&ust=1727329093925000&usg=AOvVaw3waxETwmnRpURc2UylOPz E">security camera that won't have mains + adapter nearby. The specs are 9.0V/0.6A (DC Power).

So I figure 3S to provide ~12V and lots of charge. 

I already have the camera, and an old e-bike battery so I thought I'd break down the big battery into the 18650s, and create a new small battery for use here. I'm familiar with DC electronics and lithium (lion & lipo) cells, though I've only built little things with cheap boards from AliExpress. I want a proper one with under/overcharge protection and balance charging for this project. 

As someone who has built a solar system, I am familiar with most of this stuff. If you go the 18650 route, first you have to find a reliable source. I have one if you want to know. Your bike batteries will most likely not be fakes and I have no idea if they are protected. As the protected cells are slightly longer, I recommend you establish a supply chain for the batteries (you will need to reorder several times a year) before acquiring a battery box.

Those cells come in 1 of 3 chemistries, none of which are LiPo. The 3 are NMC, NCA both 3.6V and are sub-chemistries of LiIon, LiFePO4 the safest at 3.2V. As you can quickly see, none are 12V but you only need 9 so no worries. My good 18650's have 3,300 mAh so your 600 mA load would run 5 hrs but I doubt your cameras would be at 600 mA continuously. You need to do a load test for several hours to establish an average load. I need to check if my 18650's are protect ted, I thnk they are but I need to be sure before recommending them.

As far as protection, if you get protected cells (longer) they are protected as follows

protects the battery against common dangers, such as overcharge, over discharge, short circuit/over current, and temperature.  

For 18650 one of the best chargers is the SkyRC MC3000. It will do all your cylindrical batteries of every chemistry. The charger is programmable, I just did a special program for my new Sodium batteries.

If you plan on charging insitu then I will forward a copy of the special circuit you need to both charge and discharge at the same time. Most published versions of this circuit have it wrong.

The c ost of the standard security camera batteries plus charger is much less than just the 18650 charger. BTW, my 18650's cost about $5 each when ordered 20 at a time. $53.99 for 10 and free shipping. Marked as 3,500 mAh but my testing showed them as 3,200 to 3,400, very acceptable.

Let me know if I can be of further assistance.

Hi @will,

  Bernard was indeed a great character as well ... very cleverly placed between the two main combatants, whilst never being sure of which side to be on ... and hence cast as someone who could, at the same time, appear to both combatants as being on their side, without being unduly treacherous to either.

@davee Thank you. To be honest I hadn't done the capacity calcs yet. Silly I know but I was dead keen to start implementing that I forgot this important part. Thanks for making it plain for me to see.

I just thought - hey there's a problem + I have some spare stuff = simple off-the-top-of-my-head solution.

I'll rework what I'm looking for, but thank you again for your great answer. Perhaps I'll have to lay a mains cable after all 🙂 have to buy a battery camera for this one location.

😀

Hi @pixel8,

  I hope the discussion is useful to you and has not been too negative.

  Obviously, if you can find a camera with low current consumption, then battery becomes more attractive. I can only make a wild guess as to how much current the camera you mentioned consumes, but I suspect continuous 24x7 operation of a video camera, plus WiFi etc to transmit the pictures, will be challenging for 1-3 18650 cells. In some circumstances, hybrid systems using something like a PIR detector to 'wake up' a camera are sometimes useful, but obviously that presumes it is ok to only run the camera when there is a human or large animal nearby to trigger it. Other schemes that 'wake up' on some trigger basis are also useful in some circumstances.

Obviously, running a mains cable raises several issues, including safety. Again, different circumstances require different solutions, but a possible thought for some cases is to reduce the voltage to be transmitted externally, to a low voltage. When considering such a possibility, remember to check the voltage drop if the external wire is long, but sometimes compromises to accept a volt or two drop, are possible by transmitting at (say) 12V, and then using a voltage regulator at the camera to allow for the loss.

Just a few thoughts for you to ponder. I wish you success. Best wishes, Dave

@davee Not at all. It's been a great discussion. If anything it's reinvigorated my hobby! I already have some larger LIPOs I got a while back that I'd forgotten about. I will now play and experiment. I'm confident in running mains (as I've rewired a whole house in the UK before). Thank you.

@pixel8 The direct answer to your original query is you don't need a BMS if you use protected 18650 lithium. IF you plan on using them in parallel however then you do.

I see you are in NZ so I assume no temperatures below -20C otherwise the batteries will be destroyed. Once you decide on a chemistry, check for temp min/max for charge, discharge, storage.

Also, make sure you get a quality charger for whatever chemistry you choose. I use the SkyRC MC3000 for all my cylindrical batteries, it is programmable and does almost all chemistries. I even used it for the new Sodium batteries.

If you are considering a solar charger, and a charge while discharge scenario, then a special circuit must be used. I can give you the circuit but I leave it to @davee to explain.