Lipo saver - cut off circuit.

Practical Electronics magazine - November 2021.

This looks like a good circuit for Lipo users since it will prevent wrecking your Lipos because of excessive discharge. (Happened to me once and its annoying.)




This is a fragment of the article which looks promising. A comparator to monitor battery voltage and a Mosfet to switch on and off. Full details are in the magazine and you can order a Printed Circuit Board from them:

https://www.electronpublishing.com/

The design is for two batteries but it also shows how you can reduce the components for a single battery.

The on/off switch could also be useful for model submariners. A normally closed reed switch and a magnet will form a handy external switch.

David

I ordered two of these boards a few weeks ago and I have just built one of the circuits and it seems to be working fine at initial switch on.

https://www.electronpublishing.com/product-category/pcb-service/projects-2021/november-2021/



I have also ordered a couple of these:

12V 10A Undervoltage Protection Module Low Voltage Cut off Automatic Switch On Recovery Storage Battery Board

https://www.banggood.com/12V-10A-Undervoltage-Protection-Module-Low-Voltage-Cut-off-Automatic-Switch-On-Recovery-Storage-Battery-Board-p-1888819.html?utm_design=18&utm_email=1639055724_2324&utm_source=emarsys&utm_medium=Shipoutinform190813&utm_campaign=trigger-logistics&utm_content=leander&sc_src=email_2671705&sc_eh=de4a6caa098594c51&sc_llid=32802253&sc_lid=104858042&sc_uid=jpNDqOCzO7&cur_warehouse=CN

It will be interesting to see how they compare - small size etc.

My intention is to protect Lipos in my small subs and the Practical Electronics circuit has the advantage of being able to add a magnetic "on" switch very easily.

More later.

David

I am not having too much success with getting the PE circuit to work the way I want it too. (A lot of smoking components - the regulator and MOSFET mainly and I am running out of spares.)
I think I will give this project a rest until the New Year!

And I've just put these on order on eBay (DIY is often the difficult and expensive option nowadays!):

3s 25A 18650 Lithium Battery BMS Protection Board Circuit Charging Module

https://www.ebay.co.uk/itm/154481761875?hash=item23f7d49e53:g:ZY8AAOSwSF5gu-OM

David

have you got access to a bench psu with current limit? that should limit any fault current due to the module to a smoke-free limit. Alternative is a fuse but in electronics its well known that any transistor is 'the fastest fuse on 3 legs' but it might protect untill you get the bugs sorted.
Also a good DVM as the voltage difference between full & empty for some battery chemistry can be minimal, as I guess you already know.

The chinese sellers on ebay can do a much better job making lipo charging/regulating/monitoring circuits than i can for much less money than i can... in addition to all that, all the ESCs i use understand and work well with Lipos, so the BMS i buy are for adapting things like existing Engel ballast tank controllers, so that they don't overly deplete the Lipos i use with them.

A bit of a "wrap-up" on this, not very successful, work on putting in a Lipo protection circuit.

From left to right:

- This is the standard "3s 25A 18650 Lithium Battery BMS Protection Board Circuit Charging Module".  It works but the problem I found is that it really is a charging circuit and so it doesn't switch on initially - you need to put a voltage across it to simulate charging.

- This is the Practical Electronics circuit it also works but I didn't have much success with it because I kept on blowing up components! It is also a little large for submarines.

- The third one works but it is really for lead acid battery protection and I couldn't get the cut-off voltage to be what I wanted.

I have come to the conclusion that, on safety grounds, it is perhaps best not to have devices that turn off power to model subs. (Some may say this is "sour grapes"!)

Better to lose a Lipo than the whole sub when the piston tank loses power, for example.

So I think I will stick with just my 15A car fuse with reversed diode. (which protects against wrong connection by blowing the fuse)

David

david f wrote:

A bit of a "wrap-up" on this, not very successful, work on putting in a Lipo protection circuit.

From left to right:

- This is the standard "3s 25A 18650 Lithium Battery BMS Protection Board Circuit Charging Module".  It works but the problem I found is that it really is a charging circuit and so it doesn't switch on initially - you need to put a voltage across it to simulate charging.

- This is the Practical Electronics circuit it also works but I didn't have much success with it because I kept on blowing up components! It is also a little large for submarines.

- The third one works but it is really for lead acid battery protection and I couldn't get the cut-off voltage to be what I wanted.

I have come to the conclusion that, on safety grounds, it is perhaps best not to have devices that turn off power to model subs. (Some may say this is "sour grapes"!)

Better to lose a Lipo than the whole sub when the piston tank loses power, for example.

So I think I will stick with just my 15A car fuse with reversed diode. (which protects against wrong connection by blowing the fuse)

David

there are ways to mitigate these risks. my solar autonomous boat has batteries with high and low voltage protections that will cut off main power incase of the battery running out or getting overcharged.

To get around those issues I have 3 backup UPS modules that run the core systems in case main power goes offline, so il loose main drive and manoeuvring thrusters when i loose main power but UPS1 will keep power to the servos so I can control the sail and rudder, the second UPS module runs the guidance and control systems specifically a pixhawk flight controller and a samsung phone used for control.. the third backup battery is dedicated to the bilge pump, as it occurred to me that if water gets in and takes main power offline then the bilge pump is the first thing to stop.

on a sub you just need power to drive the receiver and ballast pump to get you to the surface so a single UPS would probably be enough.
https://www.ebay.co.uk/itm/255077052656

The results of a an email exchange with Paul & Alan (Thanks both!)

It serves as a useful reminder of the danger of using Lipos (But I do use them myself and I note that most of the fires are connected with E-Scooters.):

" Hi Alan,

Paul Brassington copied this to me. Would it be alright if I post it ,as below?

David Forrest

Hi

London Fire Brigade attended 120 fires caused by Lipo type of batteries last year and 25 involving lithium batteries so far this year.

This video shows a fire that originated in the LiPo battery of an E-Scooter stored in the front room, watch for the over pressure from the bedroom windows at the beginning....

https://content.invisioncic.com/r275785/monthly_2022_02/e0aff130-ffaa-4813-a8c7-07de9c24a545.MP4.7e2c2aa7a1858e2fe69b56469ffed3b2.MP4

Kind regards

Alan Woodward

Colwyn Model Boat Club "

david f wrote:
The results of a an email exchange with Paul & Alan (Thanks both!)

It serves as a useful reminder of the danger of using Lipos (But I do use them myself and I note that most of the fires are connected with E-Scooters.):

" Hi Alan,

Paul Brassington copied this to me. Would it be alright if I post it ,as below?

David Forrest

Hi

London Fire Brigade attended 120 fires caused by Lipo type of batteries last year and 25 involving lithium batteries so far this year.

This video shows a fire that originated in the LiPo battery of an E-Scooter stored in the front room, watch for the over pressure from the bedroom windows at the beginning....

https://content.invisioncic.com/r275785/monthly_2022_02/e0aff130-ffaa-4813-a8c7-07de9c24a545.MP4.7e2c2aa7a1858e2fe69b56469ffed3b2.MP4

Kind regards

Alan Woodward

Colwyn Model Boat Club "

120 fires out of millions of batteries, you have a higher chance of your car spontaneously combusting. I suspect most of those fires were caused by the battery being improperly handled, usually by charging incorrectly or the battery being modified or damaged.

I suspect 90% of all lipo home fires are the cheap chinese scooters that were all the rage for christmas a few years ago that have turned out to be rather hastily built POS, and were even removed from sales and recalled by amazon.