Need help with Low voltage protection circuit

[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.

[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.

[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

[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

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

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.

[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.

[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

Do you have the schematic in your post 21?

[budm]

Re: Need help with Low voltage protection circuit

Thanks for posting this I will read it more details later

I just start playing with the BMS after reading some of your threads.
I bought 1s, 2s, 3s, 4s BMS with and without balancer (not apply to 1s of course).
What I found is that the one without Balancer will stop charging when one cell of the series cell Voltage reaches 4.2V first but another do not then it stop charging, so other cell are not fully charged.

[flinx]

Re: Need help with Low voltage protection circuit

Do you have the schematic in your post 21?

not as such, I basically copied it from a physical specimen directly in to the easyeda program. I skipped making an actual schematic. I have not triple checked that it is correct.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

I just start playing with the BMS after reading some of your threads.
I bought 1s, 2s, 3s, 4s BMS with and without balancer (not apply to 1s of course).
What I found is that the one without Balancer will stop charging when one cell of the series cell Voltage reaches 4.2V first but another do not then it stop charging, so other cell are not fully charged.

Some BMS balancing protection boards are very touchy in that if your gets close to voltage cutoff the charging current drops off considerably which if you do have a way to test batteries in the way I was talking about earlier you might be better off using just a regular protection board


This is the problem with protection board in general this is why it is important to get the batteries that are going to be used with the same voltage roll off —>voltage and milliamperes hour results are as close as possible to get this best results for charging and discharging cycle

Now if you are using new batteries this not as much of a problem as if you are using used batteries

[budm]

Re: Need help with Low voltage protection circuit

Some BMS balancing protection boards are very touchy in that if your gets close to voltage cutoff the charging current drops off considerably which if you do have a way to test batteries in the way I was talking about earlier you might be better off using just a regular protection board


This is the problem with protection board in general this is why it is important to get the batteries that are going to be used the voltage roll off —>voltage and milliamperes hour results are as close as possible to get this best results for charging and discharging cycle

Now if you are using new batteries this not as much of a problem as if you are using used batteries

That is why I ask about the battery tester and you recommended one for me but I do not have the money right now to buy one.

[budm]

Re: Need help with Low voltage protection circuit

not as such, I basically copied it from a physical specimen directly in to the easyeda program. I skipped making an actual schematic. I have not triple checked that it is correct.

If I see the schematic then I may be able to tell you where to add resistor for the Hysteresis.

[sam_sam_sam]

Re: Need help with Low voltage protection circuit

That is why I ask about the battery tester and you recommended one for me but I do not have the money right now to buy one.

I know it is a little bit price-e I just happened to have bonus money when I bought the first one and I really did not think that it would make that much difference using this type of battery testing device to put battery packs together but it does make a difference

Because I was just using a IMAX B6 version 2 before I bought the battery tester I was talking about earlier
You could do this way and have milliamperes results with this device which solve half of the problem

Now to get the voltages roll off is not so easy but if you are watching the discharge cycle when it to where the current start dropping off quickly and note the milliamperes hours reading and the amount of elapsed time results at this point you kind-a do the same thing about the voltage roll cutoff reading one note this approach is not quite as accurate but it could be doable but if you have the patience to do it me personally I do not have this much patience for this when you are testing high milliamperes hours batteries

Because what makes it difficult to get the voltage roll off with this device is that with this device it maintains the voltage output at a set point of 3.2 volts and drop the current output and when the current output is about 10 amps it stops

Let say that you set the amperage for one amp and are watching the display and you see the amperage drop to 900 milliampere this would be your voltages drop off starts but you would not have what the curve would be but this would give more information than if you just set the device and just read the results when the device is done with the discharge cycle you would also want to look at the charging current roll off as well because some time they are different milliamperes hours and elapsed time

One thought before I saw this battery tester that I have now

Was to take a micro controller and plot the time it takes for the voltage to drop from 900 milliamperes to when it gets to 500 milliamperes because below this value the voltage drop very quickly any way

I hope that this information will help you

[eccerr0r]

Re: Need help with Low voltage protection circuit

Post 21 circuit will eventually fail at 20V with a 12V relay due to power dissipation of the relay. A 24V relay would be marginal.

Horrible design, granted it was a trivial reverse engineer.

[flinx]

Re: Need help with Low voltage protection circuit

If I see the schematic then I may be able to tell you where to add resistor for the Hysteresis.

ok I whipped this up


a relay can be subbed for the buzzer.

[flinx]

Re: Need help with Low voltage protection circuit

Post 21 circuit will eventually fail at 20V with a 12V relay due to power dissipation of the relay. A 24V relay would be marginal.

Horrible design, granted it was a trivial reverse engineer.

edit: what's horrible?

[eccerr0r]

Re: Need help with Low voltage protection circuit

Depends on the specific relay you use and the mechanical variation between units to tell what voltage it will engage at. I have a few 24 V relays that are worthless at 12V, they will not pull at all.

The idea of hysteresis is to provide some feedback from pin 1 to pin 3 of the IC with a resistor, however you will need to add a resistor between the zener and pin 3 of the IC because it would otherwise have no way to increase the threshold. Looking at this, you will likely need to use the other amplifier in the LM358 to provide more consistent triggering, mostly because the voltage output of the LM358 will depend on the setpoint...

Modifying for MOSFET use, you will need to be careful of going near the VGSmax limit of the device. It's actually fairly trivial but the key component is that LM358, without it you will not get the gain needed for reliable on/off.

The full Li-ion battery protection (charge and discharge, as well as balancing) I designed using LM358s and LM324s ended up drawing a considerable amount of current and thus unacceptable for real implementations. However it does do the function needed, though I did design for 4S. I suspect modding for 5S won't be too hard but will require more amplifiers - luckily LM358/LM324s can go 30V+ single ended. In commercial designs they will not be using LM358s and LM324s because they eat too much power, along with the voltage references (discrete zeners need to be carefully designed between noise and power consumption.)

[budm]

Re: Need help with Low voltage protection circuit

"The idea of hysteresis is to provide some feedback from pin 1 to pin 3 of the IC with a resistor, however you will need to add a resistor between the zener and pin 3 of the IC because it would otherwise have no way to increase the threshold. Looking at this, you will likely need to use the other amplifier in the LM358 to provide more consistent triggering, mostly because the voltage output of the LM358 will depend on the setpoint.."

+1

OP: your circuit looks to be from here: https://www.instructables.com/id/BATTERY-LOW-ALARM/

BTW, using compactor IC such as LM393 with open Collector output is more suitable than using OPAMP.
You can also look into MAX6457 but it is SMD.