Need help with Low voltage protection circuit

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

http://liionbms.com/php/wp_lovtg_cutoff.php
You cannot find 5S, 6S BMS 20A, 30A, 40A with or without Balancer?
Motor will have high in-rush current to keep that in mind also.

Thanks for posting this I will read it more details later

[budm]

Re: Need help with Low voltage protection circuit

http://liionbms.com/php/wp_lovtg_cutoff.php
You cannot find 5S, 6S BMS 20A, 30A, 40A with or without Balancer?
Motor will have high in-rush current to keep that in mind also.
Vacuum is just one type of load.

[flinx]

Re: Need help with Low voltage protection circuit

The problem is there is no generic solution unless you make a really complicated circuit. Hence you need a problem for this solution, you can't make a solution searching for a problem.

So we need a problem that a solution needs to be found. Right now it seems you only have an academic problem, and all we can give is an academic solution.

I appreciate your input.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

Do the BMS work without the balancing circuits connected? if so I could just use that.

I do not want to build battery packs if I do not need to.

You can just buy protection board and for the most part they work however the problem you can run into is if your batteries are not balanced your running time can greatly lower

You can somewhat overcome this problem with a battery tester that tell you what the milliamperes hours each battery that is tested but you have to do a little bit more work up front

Now with a BMS balancing protection board the balancing of batteries is even more important than just using just a protection board only
with this BMS board you have one step you must follow and that you have to make sure that your discharge roll off voltages are very close to each other as well as milliamperes hours

You have use a special battery tester for doing this type of testing

One note the battery pack that I have mentioned earlier you can get very good results from them they do use brand name batteries other wise I would not have recommend them there battery protection board or if it has the BMS balancing function on them works pretty good from what I have seen ( the run time results are what I would expect from the type of batteries used

Yes I do take these battery packs apart to see what batteries are used

[flinx]

Re: Need help with Low voltage protection circuit

Do the BMS work without the balancing circuits connected? if so I could just use that.

I do not want to build battery packs if I do not need to.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

If you were making a battery pack there are BMS balancing protection board out there that can handle up to 100 amps the can be little bit big but the 40 amp version are some what smaller

I understand your problem because I have a 24 volt soldering iron that I want a 24 battery pack to build but the products out on the market for soldering iron did NOT work correctly which I was very disappointed with the the results

Granted I did not spend very much money for BMS balancing protection board
The problem with the BMS balancing protection board that were recommended did NOT keep the batteries balanced like advertised so results were terrible

Then the same company has a new version of the battery operated soldering iron the results of this board is a lot better but the cost was a lot more money because the quality of battery were not was advertised but when I get some time I will put together a name brand batteries and have a google working unit

I would recommend that you build a battery pack with a good quality BMS balancing protection board and just use a cord to the outside and use it that

This is what I have done for my soldering iron the battery pack and the charger unit I posted earlier is what I did so I could use the soldering iron on battery power

But with setup I can power what ever I want because what I used which I did not post was a USB power bank that uses the battery pack which I modify for this purpose so yes I did spend some money on this setup but I could use for many different devices and when I was doing this modification I had this in mind


Now if you are only want to use 20 volt instead of 24 volts I have a setup you can do which has all the parts you need to do it

The battery pack

The charger
( for the version I want to make I going to see how they are doing the charging circuit to see if I can modify it or not

The USB port unit

One note I am going to make a 12 volt version of the same thing that I am talking about

I going to make a power supply for some LED modules that I going to use with a 18 volt solar panels that I have

If you are interested on how to do this just let me know and I go into some details on how you do the modification

[eccerr0r]

Re: Need help with Low voltage protection circuit

The problem is there is no generic solution unless you make a really complicated circuit. Hence you need a problem for this solution, you can't make a solution searching for a problem.

So we need a problem that a solution needs to be found. Right now it seems you only have an academic problem, and all we can give is an academic solution.

[flinx]

Re: Need help with Low voltage protection circuit

One of my ideas was to use an off the shelf battery alarm. This circuit is similar to one I built a long time ago, but you can buy the alarm for a couple of dollars. It does not have a relay so I took the circuit and made my own board with a heavy duty 30 amp relay.


this board is 1.56"x 2.68"x 1.25" not ideal.
I have not ordered any boards made yet, but my test version does work.

The issue is there is no hysteresis and the off and on voltages are almost the same.

I Do not know enough to modify the circuit to get a 1 or 2 volt spread in the on off.

That's why I decided to try the mosfet circuit.

Through hole components are preferred as any one can make it.

[flinx]

Re: Need help with Low voltage protection circuit

this device has nothing to do with battery packs in so much as it would just protect them from being over discharged.

The idea is to be able to use battery packs that do not have protection (there are lots of these) or LIPO packs which do not normally have protection.

I cannot provide pictures as I do not have any device at the moment.

I will give you an example:
Black and decker makes a cordless vacuum cleaner called the dust buster (you may have heard of it). It runs on 16.8v (yes I know I need 18 to 21 but this is just an example).
It has a 4 cell 18650 pack inside that dies after about 2 years because the amp draw on it is 11amps continuous when in use.

When it dies the batteries could be replaced with better batteries OR one could install an adapter on the back for a makita or other 14.4v battery if one were to purchase the cheap chinese version they do not have battery protection in them, heck many of them do not have cell balancing.

The issue is that repairing the vacuum with new batteries (of legit quality) is about the cost of just buying a new vacuum.

Were one to be able to use already owned battery packs one could save a lot of money not having to buy a new vacuum cleaner every 2 years.

This is only one example.

I want to be able to take a device that might have bad batteries and refit that device for using other battery packs allowing the continued use of said device for longer.

The problem I keep running in to is that if I did want to do this ONLY for said vacuum there are devices out there and I would not be asking on forums for help.

Because I would like to do this for 18/20v devices I cannot find a reasonably priced solution. This has turned in to a quest. I generally post questions like this on forums when I have exhausted all other avenues (that I can think of) I then try forums for ideas that I may not have thought of OR sometimes I just don't know the name of the device or circuit I need.

Once I get what I am looking for I post all the information, schematics, and what not on a blog or said forum and my youtube channel so others might be able to use the information and thus save themselves much money and rage in the long run.

Please forgive me if my post sounds angry or whatever tone does not translate in text. I do this a lot, I eventually find or make what I want but sometimes it takes me a while to gather the required knowledge and materials.

PS. the devices would not be stored with batteries attached.

[eccerr0r]

Re: Need help with Low voltage protection circuit

So how much time do you expect the low voltage cutoff to occur and when you *actually* want to charge the pack, mind that with this cutoff design you have to bypass it to actually charge it (unless the drop/loss through the body diode is acceptable, which is not in most cases for lithium packs.) Also keep in mind if you charge and put the pack in cold storage for a week, your cutoff eats power and can still kill the battery that way too. I'd say most common off the shelf parts through hole design will end up emptying out a full pack in a month, and after it empties it, will continue to overdischarge the pack, defeating the purpose of the protection.

In any case I still don't get it: most if not all lithium ion packs available out there have overcharge/discharge protection. Even my HFT cheap crap Li-ion pack. This is due for liability purposes, having packs immolate due to overdischarge is not going to be safe.

Or is this a homemade pack? In this case your design is still insufficient to fully protect the pack.

Also if size is a problem, through hole is not small either, especially with the number of components needed to properly do voltage protection.

What *ARE* you trying to do specifically? Pictures would be good.

Okay I have to make it clear of my question: What is your battery pack. What are you powering with the battery pack. How much are you planning to use the device. Are you going to be leaving the device in a drawer for a few weeks when you're not using it.

[flinx]

Re: Need help with Low voltage protection circuit

It is kind of bizarre there are devices used for RC racing cars that have low voltage cutoffs, they make them for 2, 3, 4, 6, 7,and 8 cell lipos, yet for some odd reason they skip 5 cell which would work perfectly for what I need.

[flinx]

Re: Need help with Low voltage protection circuit

What BMS balancing protection board are you using
Also can you please post what you are looking for that cost $200.00

I am not using any particular board. If the battery pack has one I do not know what it is, I would also be using 18650 packs that would not have a BMS.

I looked in to BMS, BEC, and UBEC options none of them could handle the amps needed or were the wrong voltages, and I do not want to use the device to charge the batteries, nor do I want to build battery packs.

this is a listing for the board in question there are 3 options.
all 3 are very pricey and the boards are covered to prevent seeing the secret inards.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

What BMS balancing protection board are you using
Also can you please post what you are looking for that cost $200.00

[flinx]

Re: Need help with Low voltage protection circuit

Take a look at this device

https://www.ebay.com/itm/Battery-Mod....c100276.m3476

I have tried some of those devices, the problems with them are that they are too large to fit inside of tools and devices, they have displays that draw power and cannot be turned off. That one is meant for controlling the charging of a battery not running a device and then cutting off power.

I have some voltage alarms that might be hackable to do what I want with the addition of a relay. I was hoping to use a mosfet to save space. My limited knowledge of them led me to believe they were an instant on/off type O' thing, but I have since learned that is not the case.

I have spent 2+ weeks searching for anything and everything and using any combination of words regarding battery protection, under voltage, low voltage, cut off, etc. I have found many devices that do what I want but they all are just outside of the voltage, amperage, or price range of what I need.

There is one company that makes exactly what I want but I'm not paying $200 for it. I was going to design my own circuit board but I held off till I could test some designs and that's when I found that most if not all of the circuits I could find do not function as the person who posted the information claims, do not work at all, or only sort of work.

I like to keep things as simple and as small as I can, and avoid using things like arduinos to do things that such devices would be overkill.

as usual I have apparently tried to do another project that has turned in to a quest for unobtainium devices.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

Take a look at this device

https://www.ebay.com/itm/Battery-Mod....c100276.m3476

[flinx]

Re: Need help with Low voltage protection circuit

Are you looking to charge the battery batteries or something else

No the device would just be there to add over discharge protection when used on devices or with batteries that do not have that.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

There might be other solution to this problem

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

Are you looking to charge the battery batteries or something else

[flinx]

Re: Need help with Low voltage protection circuit

What are trying to power with this battery pack

Depending on what your power requirements are you might not have to reinvent the wheel

anything that require 18 to 21 volts in the category of power tools. but it could also provide power through a buck convert to whatever I might want.

the annoying thing is that there are many devices that do this but they are either not the correct voltage range or cost over $100

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

This device would run off of a 5 cell 18650 battery in series.

What are trying to power with this battery pack

Depending on what your power requirements are you might not have to reinvent the wheel
If you are just wanting to charge the battery pack