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Finally found a LiFePO4 BMS with Low-temp Charging Protection

I have a question and yes its probably a stupid one. The new BMS that you found will it stop charging when the cells are at full charge? I just can seem to get that thru my head. I plan to use the 4S LiFePO4 battery with BMS as a "remote" power source (no solar no full time charger) for use with my Ham Radio that draws max 41Amps during transmit at field locations. I was planning to re-charge when I get home with a standard auto charger (if this is okay)...Please give me advise below Thanks, S-N
 
SolarNewby said:
I have a question and yes its probably a stupid one. The new BMS that you found will it stop charging when the cells are at full charge?
Click to expand...
No such thing as a stupid question. In fact, your question points out a very important distinction.

The most BMS will shut off charge input to protect the battery if it detects one of the cells is at too high of a voltage. This should be considered an error state and should be avoided. Your charge controler(s) should be the device(s) that decide the charge is complete and to stop charging before the BMS shuts down charging.

SolarNewby said:
I was planning to re-charge when I get home with a standard auto charger (if this is okay)...Please give me advise below Thanks, S-N
Click to expand...

Be sure that whatever charger you use has a charge profile that is appropriate for LiFePO4. A lot of standard automobile chargers assume Flooded Led Acid (FLA) and will over charge LiFePO4
 
I have the 80 amp version of this bms and it has worked great for me.
20190912_000925.jpg
I was having some issues with the BT connection in that my galaxy s10 was dropping signal quite often. I ended up using an old s4 I had laying around it it worked flawlessly (probably something to do with the s10s low energy bluetooth) except when my pack is at a low SOC which is probably a saftey feature. At that point I just connect the bms to my computer to get readings. However, the updated APK you provided has now allowed my s10 to stay connected (thanks @Will Prowse).
The main issue that I've been having with this bms, however, is the capacity monitor being very finicky. Anytime I make changes to the parameter settings, my SOC reading changes and does not show true capacity. I have to fully discharge and recharge to reset it. Very annoying but I plan to remedy this by adding a coulometer to my system at a later date. Anyone else have this problem?
 
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FilterGuy said:
No such thing as a stupid question. In fact, your question points out a very important distinction.

The most BMS will shut off charge input to protect the battery if it detects one of the cells is at too high of a voltage. This should be considered an error state and should be avoided. Your charge controler(s) should be the device(s) that decide the charge is complete and to stop charging before the BMS shuts down charging.



Be sure that whatever charger you use has a charge profile that is appropriate for LiFePO4. A lot of standard automobile chargers assume Flooded Led Acid (FLA) and will over charge LiFePO4
Click to expand...
Does the BMS prevent overcharging?
 
Ralo said:
Does the BMS prevent overcharging?
Click to expand...

Yes, a properly set up BMS should prevent over-charging, but it is intended as an if-all-else-fails prevention. You should set your charger(s) to stop charging before the BMS shuts down.
 
@Power4life .... I have that same issue with the one that came installed in my battery. It seems the SOC tracking gets flushed when writing the paramaters. It initially defaults to using the battery voltage as a guestimate for SOC. If you look at the paramaters, there is actually a table for that. The good new is that once you are done adjusting settings and do a full charge it tracks well from there.
 
Power4life said:
I have the 80 amp version of this bms and it has worked great for me.
View attachment 5578
I was having some issues with the BT connection in that my galaxy s10 was dropping signal quite often. I ended up using an old s4 I had laying around it it worked flawlessly (probably something to do with the s10s low energy bluetooth) except when my pack is at a low SOC which is probably a saftey feature. At that point I just connect the bms to my computer to get readings. However, the updated APK you provided has now allowed my s10 to stay connected (thanks @Will Prowse).
The main issue that I've been having with this bms, however, is the capacity monitor being very finicky. Anytime I make changes to the parameter settings, my SOC reading changes and does not show true capacity. I have to fully discharge and recharge to reset it. Very annoying but I plan to remedy this by adding a coulometer to my system at a later date. Anyone else have this problem?
Click to expand...
Ha ha, I noticed that too - an annoying bug. I'm adding the AiLi battery Monitor voltmeter Ammeter

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hey guys - I just installed the latest version of the IOS app for the BMS. It looks like all the problems have been addressed in this version. Oh I bought the $5.00 paid version so that I could program the BMS from my smart phone.

It was so easy - all I did was download the app, connect up the BMS and the app discovered it immediately and connected the Bluetooth. No password, no initializing by connecting a charger etc.
 
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Turning off the BMS??

Normally I never turn off the BMS once it is set up. However I have a situation where I will be storing the batteries for an extended period. They will be totally disconnected from all loads and charge controllers. I would like a way to turn off the BMS without disconnecting it. Is it possible to do put a switch on one of the lines and 'turn it off'. I have heard stories of blowing out BMSs if they are not hooked up in the right order so I know I have to be carefull with this. I really don't want to experiment with a BMS to see what works and what blows things up so if any of you know if it is possible on this BMS, I would love to hear from you.
 
If your balance harness has a single Molex plug just unplug it. Then just disconnect the battery @ 50% SOC by discharging vs charging.
 
I notice the datasheet shows overcurrent is 10A over continuous current. How much higher does the APP allow you to adjust it? I just want to make sure this can handle short duration inrush currents.

Does anyone know if the 16S can be configured as a 4S to gain the additional continuous current ratings? I just asked the manufacturer but I might not hear from them until the Chinese New Year is over.
 
Decreased voltage will not lead to a higher current carrying capacity for the BMS. The limiting factor is the heat in the MOSFETs. That heat is from resistive losses in the MOSFETs, independent of voltage.

A BMS built for 16S will need to have MOSFETs that can handle a voltage of >60V. A BMS for 4S will have MOSFETs with a much lower max voltage.

A lower voltage MOSFET has a lower resistance than a higher voltage one. In theory that means that it's easier to build a lower voltage BMS that can handle higher currents. In practice it means that the lower voltage BMS just has fewer MOSTFETs in parallel.
 
SCClockDr said:
If your balance harness has a single Molex plug just unplug it. Then just disconnect the battery @ 50% SOC by discharging vs charging.
Click to expand...
I haven't tried this yet, but possibly removing only one lead on the balance cable (i.e. insert switch) might work. I'll try this later today.
 
wjbender said:
I haven't tried this yet, but possibly removing only one lead on the balance cable (i.e. insert switch) might work. I'll try this later today.
Click to expand...
OK tried removing only one balance lead and that did not work - I removed the negative lead.
 
Not that I am any expert or have a ton of knowledge so take this with a grain of salt, I recall reading in a couple posts I have found online that it is recommended to connect the black negative wire for the balance harness before the positive leads. One I recall reading said that some BMS's have a longer negative pin so it will make contact before the positive pins. Without this, there is a risk of damaging the BMS. If you "switch" off the negative wire and then reconnect it, it is basically the same as connecting the plug and having the positive terminals connect before the negative.

Again, only going by what I have read but wanted to share this warning, just in case.
 
I have heard that as well..... and empirical evidence seems to say it does not matter. That is why I am asking the smart community of Willites before I try things.

I always like to understand why something does or does not work. It helps avoid hitting the issue in other ways and sometimes opens up ways of getting around the problem. Unfortunately, BMSs tend to be black-boxes and getting any info on their internal circuity is difficult at best.

Do you recall any detail on why connecting negative last can hurt the BMS?
 
I'm not a good person to ask. I think the idea of EVER switching the ground wire is a bad idea. It violates one of the basic rules of electricity.
 
Bob B said:
I'm not a good person to ask. I think the idea of EVER switching the ground wire is a bad idea. It violates one of the basic rules of electricity.
Click to expand...
With DC removing the battery NEG from ground is best practice.
Once the battery NEG is lifted from ground it is not possible to short any POS to NEG through ground.
If you lift the battery POS & accidentally touch a grounded item you are in for a dramatic light show or far worse with solar or a charger active.
Dripping the NEG cable on anything but the battery POS will result in nothing.
 
@SCClockDr .... I understand what you are saying .... It's just that when I studied electricity / electronics many years ago. One of the basic rules was to never switch the ground wire.
If you get used to doing that and then do it in an AC circuit or a high voltage DC circuit ...it could get you killed ....If you touch a device that has the common shut off ... you become the path to ground.
 
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