Hi guys! I'm planning to use ZK-4KX buck-boost converter as CC CV battery charger DIY for LiFePo4, Lithium Ion, lead acid batteries. Input will be 20V, 80W laptop charger.

Does ZK-4KX have built-in internal protection on its output terminals to prevent damage from reverse currents in case of power failure e.g. blackouts?

A blocking diode on output terminals offers good insurance but will introduce a voltage drop of which I'm trying to avoid, if possible.

 

Welcome to AAC.

Initial searching doesn’t reveal. proper datasheet for the 20th Natural ZK-4KX, only listings for sale. In those listings “output backflow prevention” is one of the protection features listed. This sounds like what you are looking for, but it is impossible to be certain.

If you are going to charge batteries with this very cheap device, it is critical that any Li-based cells/batteries have their own, on-board protection against overcharge. While the ZK-4KX will probably operate reasonably well as a charger, you can‘t count on it from a safety perspective.

You also need to take charging best practices seriously. Li battery fires are the result of thermal runaway and this can happen in two principal ways:

‣ Damage to a cell or cells leading to an internal short circuit which in turn overheats the cell and causes a rupture of the cell casing due to the pressure of boiling flammable electrolyte subsequently ignited by the arcing of the short.

‣ Internal short circuits caused by dendrite formation associated with over-discharge. These metallic dendrites are conductive but not enough so to cause what appears to be excessive current draw. During charging these sites heat up until the thermal runaway process begins. These fires are caused by the charger but made possible by a lack of over-discharge protection on the cells. Li batteries with cells that have been discharged below about 1V are inherently dangerous to charge.

The first category is not a matter of charging or discharging but the second is entirely about that. Li battery fires that destroy property and kill people are caused by inadequately protected cells and badly designed chargers (or not even designed at all, as in the case of the ZK-4KX).

If you are going to use this thing as a battery charger you first need to learn about the best practices for charging. This includes electrical concerns such as checking cells for over-discharge, adding protection boards if not present, proper maximum charge currents, and other things. And, mechanical concerns such as checking the cells for physical damage, using a fire resistant container for cells/batteries under charge, and keeping an appropriate fire extinguisher on hand.

Note that Li battery fires are not metal fires, nor are they electrical fires in the usual sense. They are flammable organic solvent fires. An ABC extinguisher is the appropriate type. For low voltage batteries (generally under 50V), there is little concern for electric shock injury—above that normal HV precautions must be taken.

Extinguishing a Li battery fire involves removing the heat from it. It will not go out if you just eliminate the immediate flame. Most effective is drowning the burning part in water until it is cooled below a combustion-sustaining temperature. Li fires can and will restart hours later if there is still damage or residual heat. Once the battery appears out and cool enough to handle, submersing it in water several times its own volume can prevent such restarts.

Why all the text? To drive home the risks of doing what you propose in the absence of adequate knowledge and preparation. Li battery fires are extremely hot and not amenable to our usual methods of extinguishing “ordinary” household fires. I really can’t recommend what you are proposing. I realize that many people do this, but while the percentage of cases where fires are started may be low, the absolute numbers are too big to ignore.

In addition, the outcomes are often tragic—so please consider this when making a cost-benefit determination. The cheap buck-boost converter can become a very expensive one when a fire starts.

 

It does have reverse current protection built in, according to this AliExpress listing

 

Hi guys! I'm planning to use ZK-4KX buck-boost converter as CC CV battery charger DIY for LiFePo4, Lithium Ion, lead acid batteries. Input will be 20V, 80W laptop charger.

Does ZK-4KX have built-in internal protection on its output terminals to prevent damage from reverse currents in case of power failure e.g. blackouts?

A blocking diode on output terminals offers good insurance but will introduce a voltage drop of which I'm trying to avoid, if possible.

Hi there,


@Ya’akov outlined the problems very concisely I suggest you read that post over carefully.

I can add a little background info here...

First, if you do buy one of these things I suggest you test it before using. I have to recommend buying a charger made for this however as that is the safest way to go.

Second, and not sure how much this will actually help you though, there has been some new research into the problems with lithium based cells and the findings indicated that most of the cells come out with a minor defect during manufacturing. This is something only the manufacturer can control, and now that they know about it I suspect it will be addressed by a new design that eliminates the defect.
I read this some time ago, but within the last six months. The defect came in the form of a non-uniform layer inside the cell that had 'bumps' on it and that would cause early failure and even heat and fire. Also discovered were microscopic metal particles that cause either a minor short leading to higher self discharge or total failure.

In any case, there has been a lot of attention to safety with these cells so it can not be stressed enough that safety has to be a prime concern above everything else including cost, size, availability, you name it.

There are many new battery types being researched these days and one of the key factors is safety.

 

I should have said that LiFePO₄ can fail in the way I described but they are not subject to the problem of fires that Lithium Cobalt and similar cells suffer from.

 

Welcome to AAC.

Initial searching doesn’t reveal. proper datasheet for the 20th Natural ZK-4KX, only listings for sale. In those listings “output backflow prevention” is one of the protection features listed. This sounds like what you are looking for, but it is impossible to be certain.

If you are going to charge batteries with this very cheap device, it is critical that any Li-based cells/batteries have their own, on-board protection against overcharge. While the ZK-4KX will probably operate reasonably well as a charger, you can‘t count on it from a safety perspective.

You also need to take charging best practices seriously. Li battery fires are the result of thermal runaway and this can happen in two principal ways:

‣ Damage to a cell or cells leading to an internal short circuit which in turn overheats the cell and causes a rupture of the cell casing due to the pressure of boiling flammable electrolyte subsequently ignited by the arcing of the short.

‣ Internal short circuits caused by dendrite formation associated with over-discharge. These metallic dendrites are conductive but not enough so to cause what appears to be excessive current draw. During charging these sites heat up until the thermal runaway process begins. These fires are caused by the charger but made possible by a lack of over-discharge protection on the cells. Li batteries with cells that have been discharged below about 1V are inherently dangerous to charge.

The first category is not a matter of charging or discharging but the second is entirely about that. Li battery fires that destroy property and kill people are caused by inadequately protected cells and badly designed chargers (or not even designed at all, as in the case of the ZK-4KX).

If you are going to use this thing as a battery charger you first need to learn about the best practices for charging. This includes electrical concerns such as checking cells for over-discharge, adding protection boards if not present, proper maximum charge currents, and other things. And, mechanical concerns such as checking the cells for physical damage, using a fire resistant container for cells/batteries under charge, and keeping an appropriate fire extinguisher on hand.

Note that Li battery fires are not metal fires, nor are they electrical fires in the usual sense. They are flammable organic solvent fires. An ABC extinguisher is the appropriate type. For low voltage batteries (generally under 50V), there is little concern for electric shock injury—above that normal HV precautions must be taken.

Extinguishing a Li battery fire involves removing the heat from it. It will not go out if you just eliminate the immediate flame. Most effective is drowning the burning part in water until it is cooled below a combustion-sustaining temperature. Li fires can and will restart hours later if there is still damage or residual heat. Once the battery appears out and cool enough to handle, submersing it in water several times its own volume can prevent such restarts.

Why all the text? To drive home the risks of doing what you propose in the absence of adequate knowledge and preparation. Li battery fires are extremely hot and not amenable to our usual methods of extinguishing “ordinary” household fires. I really can’t recommend what you are proposing. I realize that many people do this, but while the percentage of cases where fires are started may be low, the absolute numbers are too big to ignore.

In addition, the outcomes are often tragic—so please consider this when making a cost-benefit determination. The cheap buck-boost converter can become a very expensive one when a fire starts.

The LIFE

Welcome to AAC.

Initial searching doesn’t reveal. proper datasheet for the 20th Natural ZK-4KX, only listings for sale. In those listings “output backflow prevention” is one of the protection features listed. This sounds like what you are looking for, but it is impossible to be certain.

If you are going to charge batteries with this very cheap device, it is critical that any Li-based cells/batteries have their own, on-board protection against overcharge. While the ZK-4KX will probably operate reasonably well as a charger, you can‘t count on it from a safety perspective.

You also need to take charging best practices seriously. Li battery fires are the result of thermal runaway and this can happen in two principal ways:

‣ Damage to a cell or cells leading to an internal short circuit which in turn overheats the cell and causes a rupture of the cell casing due to the pressure of boiling flammable electrolyte subsequently ignited by the arcing of the short.

‣ Internal short circuits caused by dendrite formation associated with over-discharge. These metallic dendrites are conductive but not enough so to cause what appears to be excessive current draw. During charging these sites heat up until the thermal runaway process begins. These fires are caused by the charger but made possible by a lack of over-discharge protection on the cells. Li batteries with cells that have been discharged below about 1V are inherently dangerous to charge.

The first category is not a matter of charging or discharging but the second is entirely about that. Li battery fires that destroy property and kill people are caused by inadequately protected cells and badly designed chargers (or not even designed at all, as in the case of the ZK-4KX).

If you are going to use this thing as a battery charger you first need to learn about the best practices for charging. This includes electrical concerns such as checking cells for over-discharge, adding protection boards if not present, proper maximum charge currents, and other things. And, mechanical concerns such as checking the cells for physical damage, using a fire resistant container for cells/batteries under charge, and keeping an appropriate fire extinguisher on hand.

Note that Li battery fires are not metal fires, nor are they electrical fires in the usual sense. They are flammable organic solvent fires. An ABC extinguisher is the appropriate type. For low voltage batteries (generally under 50V), there is little concern for electric shock injury—above that normal HV precautions must be taken.

Extinguishing a Li battery fire involves removing the heat from it. It will not go out if you just eliminate the immediate flame. Most effective is drowning the burning part in water until it is cooled below a combustion-sustaining temperature. Li fires can and will restart hours later if there is still damage or residual heat. Once the battery appears out and cool enough to handle, submersing it in water several times its own volume can prevent such restarts.

Why all the text? To drive home the risks of doing what you propose in the absence of adequate knowledge and preparation. Li battery fires are extremely hot and not amenable to our usual methods of extinguishing “ordinary” household fires. I really can’t recommend what you are proposing. I realize that many people do this, but while the percentage of cases where fires are started may be low, the absolute numbers are too big to ignore.

In addition, the outcomes are often tragic—so please consider this when making a cost-benefit determination. The cheap buck-boost converter can become a very expensive one when a fire starts.

Thank you for the invaluable & comprehensive guide on Li battery charging. And I agree that it's always better to ere on the side of caution.

For one, I believe that LiFePo4 are more stable compared to its Li Ion cousin in terms of charging and usage. Additionally, I have incorporated a battery management system to the LiFePo4 battery pack that protect it from o

Hi there,


@Ya’akov outlined the problems very concisely I suggest you read that post over carefully.

I can add a little background info here...

First, if you do buy one of these things I suggest you test it before using. I have to recommend buying a charger made for this however as that is the safest way to go.

Second, and not sure how much this will actually help you though, there has been some new research into the problems with lithium based cells and the findings indicated that most of the cells come out with a minor defect during manufacturing. This is something only the manufacturer can control, and now that they know about it I suspect it will be addressed by a new design that eliminates the defect.
I read this some time ago, but within the last six months. The defect came in the form of a non-uniform layer inside the cell that had 'bumps' on it and that would cause early failure and even heat and fire. Also discovered were microscopic metal particles that cause either a minor short leading to higher self discharge or total failure.

In any case, there has been a lot of attention to safety with these cells so it can not be stressed enough that safety has to be a prime concern above everything else including cost, size, availability, you name it.

There are many new battery types being researched these days and one of the key factors is safety.

Thank you for the invaluable & comprehensive guide on Li battery charging. And I agree that it's always better to ere on the side of caution.

For one, I believe that LiFePo4 are more stable compared to its Li Ion cousin in terms of charging and usage. Additionally, I have incorporated a battery management system to the LiFePo4 battery pack that protect it from overcharge or overvoltage, overcurrent, overdischarge or low voltage cut-off. BMS also has a passive battery voltage balancer.

ZK-4KX unit does not connect directly to the LiFePo4 battery pack but charges through the BMS for that extra layer of safety. As you well know, ZK-4KX is a constant voltage (CV), constant current (CC) whose output parameters can be set closely to the charging data sheets of the recipient battery.

 

It does have reverse current protection built in, according to this AliExpress listing

View attachment 304811

Much appreciated, Jon!
Glad to know that this unit has reverse current protect, no worries from power outages on the input end.

You just brought me one step to completing this project.

 

My apologies to everybody who replied to this post for my mixed-up replies. I'm a newbie on this forum and unfortunately run into some problems editing my responses yet. Thank you for your patience and understanding.

 

The LIFE

Thank you for the invaluable & comprehensive guide on Li battery charging. And I agree that it's always better to ere on the side of caution.

For one, I believe that LiFePo4 are more stable compared to its Li Ion cousin in terms of charging and usage. Additionally, I have incorporated a battery management system to the LiFePo4 battery pack that protect it from o

Thank you for the invaluable & comprehensive guide on Li battery charging. And I agree that it's always better to ere on the side of caution.

For one, I believe that LiFePo4 are more stable compared to its Li Ion cousin in terms of charging and usage. Additionally, I have incorporated a battery management system to the LiFePo4 battery pack that protect it from overcharge or overvoltage, overcurrent, overdischarge or low voltage cut-off. BMS also has a passive battery voltage balancer.

ZK-4KX unit does not connect directly to the LiFePo4 battery pack but charges through the BMS for that extra layer of safety. As you well know, ZK-4KX is a constant voltage (CV), constant current (CC) whose output parameters can be set closely to the charging data sheets of the recipient battery.

Hello again,

Yes you are right that the LiFePO4 cells are not as bad as the Li-ion cells.

What you might do then to follow up is simply read up on the proper charging of these cells and see what you might learn. If you know what the proper charging regimen is then you should be able to set your controls to meet those specs. After that you have the BMS that may catch spurious out of spec transients.

 

The LIFE

Thank you for the invaluable & comprehensive guide on Li battery charging. And I agree that it's always better to ere on the side of caution.

For one, I believe that LiFePo4 are more stable compared to its Li Ion cousin in terms of charging and usage. Additionally, I have incorporated a battery management system to the LiFePo4 battery pack that protect it from overcharge or overvoltage, overcurrent, overdischarge or low voltage cut-off. BMS also has a passive battery voltage balancer.

ZK-4KX unit does not connect directly to the LiFePo4 battery pack but charges through the BMS for that extra layer of safety. As you well know, ZK-4KX is a constant voltage (CV), constant current (CC) whose output parameters can be set closely to the charging data sheets of the recipient battery.

Hello again,

Yes you are right that the LiFePO4 cells are not as bad as the Li-ion cells.

What you might do then to follow up is simply read up on the proper charging of these cells and see what you might learn. If you know what the proper charging regimen is then you should be able to set your controls to meet those specs. After that you have the BMS that may catch spurious out of spec transients.

Advice much appreciated.

For me, that's the advantage of using a programmable CC CV power supply unit; much like a bench power supply, it can be set to charge most battery types based on their data sheets charging recommendations. The correct max. voltage and current are then fed to the BMS and on to the batteries.

 

Advice much appreciated.

For me, that's the advantage of using a programmable CC CV power supply unit; much like a bench power supply, it can be set to charge most battery types based on their data sheets charging recommendations. The correct max. voltage and current are then fed to the BMS and on to the batteries.

Hello again,

That's the way I did it several times back when Li-ion cells were first becoming popular. I watched the voltage level carefully though to make sure the power supply kept the voltage at the right level, and of course the current at a safe level too.
I then moved on to designing circuits to do this with very precise control over the voltage and max current.
I also moved to a commercial charger that makes it very easy to charge the 18650 cells.

There is another facet to this though, and that is battery conditioning. Some chargers use more than one stage of charging, but that could be just for lead acid cells. You could check if there is such a thing as multiple stage charging for your chosen chemistry too.

 

I should have said that LiFePO₄ can fail in the way I described but they are not subject to the problem of fires that Lithium Cobalt and similar cells suffer from.

Thank you for the update.
LiFePo4 is not as susceptible to thermal runaways compared to a Li Ion, based on the specs sheets. In addition, their rated number of life cycle times are at least 3x that of Li Ions.

 

Thank you for the update.
LiFePo4 is not as susceptible to thermal runaways compared to a Li Ion, based on the specs sheets. In addition, their rated number of life cycle times are at least 3x that of Li Ions.

Hi again,

One of the things I liked best was the better safety record, but next to that I liked the weight difference between that and a lead acid battery. I think they are 1/3 (one-third) the weight of a lead acid, which makes them much easier to carry around.
One of the drawbacks is lower current draw ratings. The lead acid can handle higher currents in the same Amper Hour size battery. I think it is like twice or more.

 

You're right on all counts. The lighter weight makes LiFePo4 practical for portable operations but has the added advantage of longer service life. Lead acid are rated for 600 to 800 cycles while LFPs are nominally rated at 2,000 cycles, more if you charged them to 80% SOC max and limit DOD (depth of discharge) to 20% capacity.

 

You're right on all counts. The lighter weight makes LiFePo4 practical for portable operations but has the added advantage of longer service life. Lead acid are rated for 600 to 800 cycles while LFPs are nominally rated at 2,000 cycles, more if you charged them to 80% SOC max and limit DOD (depth of discharge) to 20% capacity.

Oh yes that's another good point. The cycle life is longer for sure, and I do not think they suffer as much from deep discharge problems like lead acid does.

 

It does have reverse current protection built in, according to this AliExpress listing

View attachment 304811

Just an update, guys. Buck boost unit has anti reverse protection at the output terminals. No anti-backflow diode needed. Live tested with an actual ZK- 4KX unit.

Thank you, everybody for your kind replies. Jon, you rock!

 

Just an update, guys. Buck boost unit has anti reverse protection at the output terminals. No anti-backflow diode needed. Live tested with an actual ZK- 4KX unit.

Thank you, everybody for your kind replies. Jon, you rock!

Hi,

Just wondering, what mechanism does it use to achieve that?
I ask because some people use a series diode, but that does not work. The only thing that works is a parallel diode, as strange as that sounds.
This is because a series diode still becomes forward biased if the output load is active and is reversed. Not all loads are like that, but if you need anti-backflow then I would say you need a parallel diode.
Also with the parallel diode (high current rated) a fuse is also a good idea. If that diode becomes forward biased it is because of the output load trying to power the output terminals, and then the fuse blows and disconnects the output from everything. Some built-in minimum load is a good idea for when this happens because boost circuits like to have some kind of load even if just a light load.

 

Been wondering about this same question too. And the circuit you suggested above seems a logical answer. It will be an interesting topic to further analyse. Thanks

 

Been wondering about this same question too. And the circuit you suggested above seems a logical answer. It will be an interesting topic to further analyse. Thanks

Hi,

You are welcome.
I have a power supply I used for charging a car battery a while back and one time I had connected a car battery backwards to the power supply just for a moment. What happened was the internal parallel diode blew out, and luckily it blew short circuit not open. The short circuit protected the power supply.
Lucky I had only connected the battery for a moment so nothing melted. There was no inline fuse.
After that happened I had replaced the diode (1N5400 series) but also added an inline fuse so that if it ever happened again the fuse would blow and that would protect the wiring from the diode to the battery just in case the diode did have time to blow out again.

It's a very simple fix although I had to find a place for the fuse. The diode is in parallel, and a fuse inline with the output wire that leads to the positive output terminal.
There is a chance that the added fuse will add resistance to the wire, so you may also have to connect the feedback line AFTER the fuse. That way the point of regulation is right at the output terminal not before the fuse.

 

You described the protection quite clearly. It would be a simple but worthy addition to any power supply cum charger. If it is not asking too much, is it possible to post a circuit diagram. It will be a big help.