Smart Switch V4 "Intelligent low voltage cutoff switch"

[isaac_alaska]

recieved mine in the mail yesterday, i need to solder the whole thing together. looks nice, and nice packaging!

[jerrysimon]

Hi as I have said these look pretty neat and I have expressed interest in a PM. I just wanted to clarify how this may have prevented my recent loss of two cells.

As explained in my main post in the battery forum I lost two cells one in each of a 2 * 6s1p pack in succession over a three week peiod. The pack was two years old and had done 500 charge cycles.

I am wondering how this unit might have avoided that given that when I measured the pack at rest 11 cells were around 3.2v and one had dropped down to below 1v ?

If it is recommened that the LCV is set to 2.75v/cell i.e. 33v for a 12s1p the pack then the above failure would still have happened as the pack would have been at 37v, or, am I missing the fact that it was at rest when I measured it and when actually using it the voltage sag would take the pack down to less than 33v ?

Ps I just found the real time (during the ride) Cell Log data I took when the pack failed and on the failing 6s1p pack, five of the six cells were at 3.15 when the bad cell went down to 2.0v i.e. this 6s1p pack voltage was 17.75v. If the other 6s1p pack was around 3.15v/cell (the all good cells would probably have been higher) i.e. 18.9v for the pack then the total 12s1p pack would be around 36.65v. So does that mean for 12s1p, A123 packs that the LVC should be set at 36-37v not 33v ?

In my case if it was set at 33v for the whole pack then its unlikely having the the Smart Switch V4 fitted would have prevented me losing the cell.

Regards

Jerry

[kfong]

For A123's, I usually set it for 2.75 volts per cell, when all cells are healthy you get proper cutoff. All cells decrease at a proportional rate. By not monitoring your packs you end up damaging the first cell or two when going below LVC. Once these are damaged your packs will no longer work as expected. Your 3.2 volts indicate more of a charged state than being empty. Your packs probably became unbalanced from earlier abuse.

Voltage sag plays a role, but you need to know the voltages soon after the sag to get a good indication of the packs resting voltage during use. Constant monitoring of the pack is easily done by the smart switch. it allows for sag so you don't get false readings and when it finally does cut off your packs should end up at 33 volts, with all cells balanced at 2.75 volts. You can tweak the LVC to obtain the final voltage depending on how stiff you battery pack is. In your case, you are running only one string of cells, not a very stiff pack. I would recommend changing the sag delay in the advance menu option to 10 seconds or less. The standard setup has a 20 second sag delay. Using only one string of cells means your capacity will drop very fast when near LVC. You have very little room for error. Perhaps even a 5 second sag delay is safer to begin with.

The whole point of a LVC is to avoid what just happened to your pack. Once your pack becomes unbalanced, the weakened cell has a tough time keeping up with the good ones and should be replaced.

Hi as I have said these look pretty neat and I have expressed interest in a PM. I just wanted to clarify how this may have prevented my recent loss of two cells.

As explained in my main post in the battery forum I lost two cells one in each of a 2 * 6s1p pack in succession over a three week peiod. The pack was two years old and had done 500 charge cycles.

I am wondering how this unit might have avoided that given that when I measured the pack at rest 11 cells were around 3.2v and one had dropped down to below 1v ?

If it is recommened that the LCV is set to 2.75v/cell i.e. 33v for a 12s1p the pack then the above failure would still have happened as the pack would have been at 37v, or, am I missing the fact that it was at rest when I measured it and when actually using it the voltage sag would take the pack down to less than 33v ?

Ps I just found the real time (during the ride) Cell Log data I took when the pack failed and on the failing 6s1p pack, five of the six cells were at 3.15 when the bad cell went down to 2.0v i.e. this 6s1p pack voltage was 17.75v. If the other 6s1p pack was around 3.15v/cell (the all good cells would probably have been higher) i.e. 18.9v for the pack then the total 12s1p pack would be around 36.65v. So does that mean for 12s1p, A123 packs that the LVC should be set at 36-37v not 33v ?

In my case if it was set at 33v for the whole pack then its unlikely having the the Smart Switch V4 fitted would have prevented me losing the cell.

Regards

Jerry

[jerrysimon]

Thanks for the comprehesive reply Kin, all that makes sense I think

Are you saying that if I discharge completly with your switch fitted it will power off at the set LVC of 33v and all cells will be balanced with a 2.75v reading ?

Getting 500 charge cycles from my pack is not bad given the abuse I obviously gave it over the two years. Now that I have replaced the two failed cells I wonder how long it will last. I guess I need to weigh up if to manually monitor/balance more, keep a few spare cells or go all out and get your clever little switch

PS This is how my setup is I wonder if your switch would fit in the pocket of my Brompton bag and replace the existing power switch. That switch must be taking quite a battering with the current surge when I first switch it on. Again something your switch would prevent

Battery in left pocket, controller in right.



Pocket open showing unbilical from from the bike to the bag.



Sorry for all the questions

Regards

Jerry

[teklektik]

... Pocket open showing unbilical from from the bike to the bag.

JS- interesting connector pair - can you afford some details?

[jerrysimon]

... Pocket open showing unbilical from from the bike to the bag.

JS- interesting connector pair - can you afford some details?

Sorry and I don't mean to hijack the thread. Its made by http://www.bulgin.co.uk/Products/GenPurpose_Connectors/GenPurpose_Connectors.html.

The unbilcal carries all my connections on this eight pole plug including three motor wires (each pin rated to 6 amps), throttle and cutout breaks. Enables me to seperate bike and bag to keep the whole thing portable.

Kin's switch would finish the whole project off perfectly

Regards

Jerry

[kfong]

The cycle life on the a123 is so high, I have yet to see one go bad on mine or my friends unless it's been abused. I've even used them on RC setups where we really task them. Seems like you have plenty of room for it. Not having a break down if it's your commute seems reason enough for me. At the very least you should install a LV alarm. Once your pack hits that point, being a single series pack, you have pretty much used up the capacity and need to disconnect since it's only 2 ahrs in useful capacity with very a small buffer left, even riding less than a block can push past whatever is left and cause damage.

Another solution is to add more capacity so you always have plenty left over before the next charge cycle.

[jerrysimon]

Many thanks Kin for the info and advice. Fitting a couple of LVAs is an option but its a hassle if I have to keep remembering to connect/disconnect them. As I said your solution is very neat and is fit and forget

I will mull it over and get back to you if I decide to go for one of your smart switches.

Regards

Jerry

[lock22]

Hi kfong

been catching up on lots of threads, and your switch looks like the business for everyday use. I currently have a 48v lifepo4 system on a cyclone kit, as you, and am using the goodrum/fechter bmc, am happy with this apart from 2 areas, size and battery deconnexion. Your design answers both these questions but I do have a 3rd; being a mac user, the windows prog is going to cause a bit of bother. Any simple solution you may have is welcome, or I suppose I can borrow a pc if necessary?
and are your boards still available?

best wishes

Charlie

[kfong]

Hi Charlie,

Yes the boards are available.

The communication is just standard serial 9600 baud (8,n,1,z). Any terminal program with serial port access will work. I'm sure Mac has several freeware stuff you can look for. You might need a USB to serial port converter if your Mac does not have a serial port. If you just plan to use it on one setup, I can preprogram it for you.

I'm finding a lot of uses for this switch. I'm currently building a 12volt car starter out of A123's for the winter, incase of a breakdown. Since there are so many things I have around the house that run off of 12volts. I can leave them plugged in to it unattended and not worry about damaging the cells. This makes the 12v car starter a lot more useful.

Hi kfong

been catching up on lots of threads, and your switch looks like the business for everyday use. I currently have a 48v lifepo4 system on a cyclone kit, as you, and am using the goodrum/fechter bmc, am happy with this apart from 2 areas, size and battery deconnexion. Your design answers both these questions but I do have a 3rd; being a mac user, the windows prog is going to cause a bit of bother. Any simple solution you may have is welcome, or I suppose I can borrow a pc if necessary?
and are your boards still available?

best wishes

Charlie

[Diamondback]

PM sent

Jason.

[docnjoj]

I've been using Kin's switch on my A123 pack and it helped me determine one cell was bad. It cut off early a few times and made me check voltages under load with a Cellog. Sure enough one cell was going down way faster than the other 11. Changed out that cell and am getting full range (> 20 miles) from the battery before cutoff. I'm using 2.75 for my LVC.
otherDoc

[Kin]

I am both happy this exists, and totally frustrated that it happens to be exactly what I was planning for a couple months to do myself. :p

[Diamondback]

received my smart switch a few days ago. (thanks Kfong )

mounted it in a nice box, soldered on the input and output wires and plugs for my application.
i am yet to install it on the trike though. will try to get that done this coming weekend.

Jason.

[migueralliart]

I wanted to purchase this a while ago but I thought it was not sold as a ready unit. Does this still apply?

[kfong]

Unfortunately I have very little time to devote to ebike stuff these days. Jason had to wait a while before I had time to build it. I have also promised another member but have yet to find time to complete it. If you are willing to wait, send me a PM and to get on a list. Maybe I can get few done once I start. No promises since I won't take any money for pre-orders. Working full time so you will have to be patient. Once riding season starts for me, then forget about it If you have electronic skills, the bare boards are still available.

[chroot]

Hi Kfong,

Count me in, if you are going make these smart switch and I would buy you 2 or 3 smart switch no time! I would love build my own and I dont have exactly good equipment like you have.

I still running smart switch on cargo ebike, After the headway battery got fire then I moved to my old Tidalforce ebike, My fiancee and I absolutely love the smart switch made so simple for us.

Let me know when you are able make the smart switch and I must have it for my cromotor racing ebike.