Smart Switch V4 "Intelligent low voltage cutoff switch"

[kfong]

I finally found the time to finish the Smart Switch. This started out as a low voltage cutoff circuit and has evolved into an intelligent switch that solves many current issues with ebikes and power management.

This replaces your master switch or large clunky Kilovac relay.

Some key Features of the standard setup:
No more Sparks when connecting up battery to system! No precharge circuit needed. Woohoo!
Low voltage cutoff but will not false detect if you do a throttle burst when getting low on capacity.
Auto Shut off. No more worrying about forgetting to shut down controller.
Switch is a complete disconnect. No standby or low voltage drain. System and everything else is absolutely switched off from battery. You can store it through the winter without worry. Set and forget!
Up to 100V and high current capable. Up to 6 IRFB4110 can be added.
User configurable. You set the Low Voltage, scale factor, time delay for auto shutoff from your PC serial port.
10bit accuracy; at 50volt scale you get .05 volts per step. At 100 volt scale you are at .1 volts per step. You define what cutoff you need, so it works with any battery chemistry.
Push button off switch can be used as an emergency off switch as well.
Status report. Serial port data stream so you can monitor the switch if you like.
All parts are through hole mounted for easy kit build.

With this switch, you can keep your ebike simple, by charging with a good RC balance charger and just rely on the Smart switch as a low voltage cutoff. With Konions, I don’t even bother with a BMS or balancing. With Lipo’s, I just charge them with balance a balance charger to keep them in check, you can run a set of Cell logs if you need to monitor them, but the newer generation Lipo’s stay balanced quite well as long as you don’t over drain them. But remember Cellogs have a constant drain on batteries and need to be disconnected when powered off, Methods recently came out with a LVC (cell level protection) setup that would work better since it has hardly any drain. The output can be connected to my board to shut down. This would then give you full protection when using Lipo's.

Other than connections to battery and motor controller. The only other external hardware is 2 push button switches that make contact when pressed. One is used to turn the system on. The other to turn the system off, or enter setup mode. I usually put the switches and the board in a small box next to the battery, or put it with the batteries and just bring out the push button switches.

The serial port adapter allows you to communicate to the PC. It does requires 9-12 volts to run, but you can try shorting the INT jumper which take power from the serial DTR pin. This is about 9volts but you need to verify that is stays high. Easier to just use a 9volt battery to be sure. Once you set the voltage cutoff, scale and timeout. You can leave it off till you need to change the parameter or monitor the status of the Smart Switch.

I only did a limited run of 28 boards. I need 8 of them for my own projects and will be selling off the rest. Depending on interest, I may do a bigger run.

The current board is missing a trace, so you need to wire that up as shown on the back side. I will post more info on this thread on building them.

Currently I will be selling:
Bare Smart Switch boards for $20
Bare Serial interface board $5
Programmed PIC for $20
Shipping is $5
International shipping $10

Built for $135, but I will leave out the connectors. You can wire them directly since there really aren’t that many connections for just the Standard Smart Switch setup.
Built Smart Switch without the serial interface $120. Pre-configured if you don't think you need to modify any parameters,

There are several options I plan to incorporate, but currently the software space is limiting me from doing so. The features I have been able do limits the space so it becomes too customized at this time to offer them. No configurable options due to lack of code space. A custom chip would need to be burned each time. There is a new chip with larger code space but my development setup is not able to program it yet. It looks like it will be a while for the compiler to support the new chip as well.

Note: These features are not available with the standard setup, when they become available, it would be just a matter of purchasing a new chip and adding the additional hardware. For now I’m just offering the standard Smart Switch setup.

Current measurement for wattmeter (Working)
Temperature sensor for battery and motor
Simple Fuel gauge meter (Working)
Simple led meter Empty, Half, and Full (Working)
Alarm buzzer (Working)
Throttle feedback
Cell log monitor

Other useful things I've done with this Smart Switch, load monitor so I don't have to sit there and unplug the battery, battery testing, small power cutoff for lights. I currently have it installed on my Cyclone ebike build and on 2 E300 Razor scooters.

[kfong]

I did a video screen capture of the setup menu. The cursor didn't show for some reason but it gives you a rough idea on setting up HyperTerminal in windows. You can use any terminal program instead of the one supplied by windows.
http://www.youtube.com/watch?v=u7ArqYBrkI8
Essentially I closed out the initial commands and went straight to the properties menu on HyperTerminal to setup the serial port. You need 9600 baud without any hardware handshaking. Then go to Ascii setup and check send, echo and append box. That should get HyperTerminal running.

When smart switch first powers up. The settings are zero. It will shut down as seen in the video. To get to setup screen you need to hold down the OFF pushbutton and then press the ON pushbutton. Release both, the setup menu should come up. There are only three parameters to set. Low Voltage cutoff, Scale Factor, and Shut down delay.

Here are the PDF's of the parts that need to be populated and the extra wire that needs to be added.

PIC BATTERY MONITOR AND SHUTDOW layout2 - annotated - flattened.pdf

Highlighted parts needed for standard setup

(35.98 KiB) Downloaded 319 times

PIC BATTERY MONITOR AND SHUTDOW bottom - annotated - flattened.pdf

Wire to be added

(28.21 KiB) Downloaded 179 times

PIC BATTERY MONITOR AND SHUTDOW layout2.pdf

Updated Silk Screen to simplify parts order

(31.78 KiB) Downloaded 170 times

PIC BATTERY MONITOR AND SHUTDOW bottom.pdf

Bottom view

(15.22 KiB) Downloaded 146 times

I've simplified the parts list and created a new silk screen to reflect this. Please follow the new silk screen when placing components.
If your pack is between 12 - 55 volts your scale factor will be .0537
If your pack is between 56-105 volts your scale factor will be .1027

[kfong]

Dimension 3.45" X 1.85"

I finally got around to the partslist with Digikey part numbers, sorry for the delays. I can now take orders.

partslist.pdf

Parts list with Digikey parts

(20.73 KiB) Downloaded 188 times

[NeilP]

Charging with the balance leads sounds like a painfully slow way to charge...what sort of charge current can you get...an amp or two at the most ...just not viable on a 20 Ah LiPo pack

[kfong]

Charging with the balance leads sounds like a painfully slow way to charge...what sort of charge current can you get...an amp or two at the most ...just not viable on a 20 Ah LiPo pack

I'm using the Hyperion 1420i with ballance leads. Only a hour to charge a 10 ahr pack. You can bulk charge them with the Hyperion, which I do as well but throw in the balance leads from time to time. This keeps things simple without needing a battery management system. Charging Lipos without balance leads is not very safe. If the packs are well balance, the balance portion isn't much of an issue.

[NeilP]

Ah, OK understand...You are not charging WITH the balance leads...you are charging with the main current leads..and using the balance leads just to balance.

Your post made it sound like you were just using the balance leads to charge

[kfong]

Think of this product as a just simple mechanical switch, but with all the features you want a switch to do!

Battery plugs into the Red and Black Andersons and the Grey and White goes to your Motor Controller. That's all the connection to your system.

[amberwolf]

About the only thing I can see that it doesn't do besides make my tea is make sure the BMS on a battery is disconnected, so taht the BMS doesnt' drain any cells in the pack it's attached to.

Not much you can do about that, unless you make a board with a FET for each cell's balance lead as well as main lead(s), and stick it in between BMS and battery, or remove the BMS and use only this (which I presume is the intent).

[kfong]

Yep, unless I build an electric car. I don't ever plan to use a BMS and have yet to use one. Too many things can go wrong, especially in the trails where the pounding abuse I put the packs through would make it unreliable. I like the wiring to be as simple as possible. As long as you stay in the 80-20 rule. The packs will rarely go out of balance, or basically just don't drain them too much, since this allows one cell to go lower than the rest if it's nearly depleted. I think a reliable low voltage cutoff is all you really need along with a good RC balance charger to charge them.

My favorite battery for carefree use are the Konions. I have never needed to balance them and I only bulk charge them. They have yet to let me down. They have been dropped from my rear rack several times while trail riding. The pounding and jarring back their is really intense. I have to tie down the pack when I ride the trails. Low voltage cutoff is the only thing I rely on.

About the only thing I can see that it doesn't do besides make my tea is make sure the BMS on a battery is disconnected, so taht the BMS doesnt' drain any cells in the pack it's attached to.

Not much you can do about that, unless you make a board with a FET for each cell's balance lead as well as main lead(s), and stick it in between BMS and battery, or remove the BMS and use only this (which I presume is the intent).

[NeilP]

Any ideas on what current this will take at 100volt?
I am seeing peaks of 120 and continious of around 50 for up to 3 or 4 minutes on climbs or long straight flats
Worried about heating of those FETS with no heatsink
The board does not seem to be setup to fit heatsinks

[kfong]

I don't really have any high power setups. The specs on the fets for just one is able to handle it if it has a good heat sink. I just gang them up to avoid having to use any heatsink. With 4 on my cyclone build. They run cool to the touch. I get more heat from the dropping resistor. I'm running 40 volts and see bursts of 40-50 amps. With 6 Fets that is more than most controllers running through one phase. The good thing is this switch is fully on or off. It is running where the fets like it best. No chopping frequency to create heat. Using 4 fets to me is overkill on my setup. I will be testing is with 12S lipos soon with only 1-3 fets to see how warm it even gets. RC cars use this arrangement with a custom heat sink on top, but again they are constantly switching. Where the smart switch is just fully on. The on resistance is so low that very little heat is generated.

[wojtek]

I don't really have any high power setups.

I would think this switch makes most sense for high power setups. That is where you get BIG spark and where extra safety features are wanted!
Personally i would be interested to get one for my high power 100v setup.

[kfong]

When I first started, I picked up some of these viewtopic.php?f=2&t=7170&hilit=Kilovac
Kilovac relays for various projects. One is currently in use to control my house sump pump since I was tired of replacing the contacts every few years. I never did put one on a ebike due to the size and it still didn't do all the things I wanted it to do. I can't think of anything I currently have that would even test the limits of (6) 4110 Fets in parallel. Any suggestions?

I don't really have any high power setups.

I would think this switch makes most sense for high power setups. That is where you get BIG spark and where extra safety features are wanted!
Personally i would be interested to get one for my high power 100v setup.

[docnjoj]

Hey Kenny
Could I use this switch for my 36 volt Konion setup with 6P Fatpacks? I think it is genius and I want one. I would prefer that you built it since my eyes are getting bad!
otherDoc

[spinningmagnets]

Great idea, kfong. Thanks for developing this!

[kfong]

It would work but the idea is to have this as you main cut off. I used my dewalt packs for testing, but it has an internal bms already, so it becomes redundant. Also the dewalt bms has a steady drain if left in the on state, so even with their bms it's not as good of a solution as having the smart switch in full control.

Is your fatpacks wired directly to the batteries or are they still factory? If they are still factory, I would set the smart switch to a lower cutoff and let the fatpack bms protect the cells. You still gain auto shut down, no sparks and emegency off switch. You can also set the cutoff higher, but you won't be using the full capacity. Come to think of it if you set it to the same cutoff, as soon as one pack goes down. Smart switch will do a complete shut down anyways. So the answer is Yes.

No problem building one. I'll set one aside for you.

Hey Kenny
Could I use this switch for my 36 volt Konion setup with 6P Fatpacks? I think it is genius and I want one. I would prefer that you built it since my eyes are getting bad!
otherDoc

[Alan B]

Nice project. I've been thinking about making a similar unit myself with a keyswitch.

A question. It looks like you may be using a latching relay. It is my understanding that physical shock can cause a latching relay to switch. Is that a potential problem here? Hitting a pothole on a bike might turn the power on or off if the board was mounted firmly to the frame in any way?

[kfong]

I trail ride, it has not been a problem, and I've mounted it directly to the frame, which had only front shocks and have been put in scooters with no suspension. If it can take the abuse I put it through I'm sure you won't make it fail. These have low mass and I suspect spring leaf tensioned. They are not the big relays you might be thinking of. The smart switch has been working for over a year on my cyclone build. I just needed more for other projects. Lots of uses for this switch. Just recently picked up a dc/dc supply Ypedal, pointed out. Will be hooking it up to my car battery and Hyperion charger to charge my spare pack while I trail ride, but I don't want to over discharge the car battery in case it's low. Smart switch to the rescue, same with my RC stuff.

Nice project. I've been thinking about making a similar unit myself with a keyswitch.

A question. It looks like you may be using a latching relay. It is my understanding that physical shock can cause a latching relay to switch. Is that a potential problem here? Hitting a pothole on a bike might turn the power on or off if the board was mounted firmly to the frame in any way?

[Alan B]

Good to hear that you've tested it and there is no problem.

I trail ride, it has not been a problem, and I've mounted it directly to the frame, which had only front shocks and have been put in scooters with no suspension. If it can take the abuse I put it through I'm sure you won't make it fail. These have low mass and I suspect spring leaf tensioned. They are not the big relays you might be thinking of. The smart switch has been working for over a year on my cyclone build. I just needed more for other projects. Lots of uses for this switch. Just recently picked up a dc/dc supply Ypedal, pointed out. Will be hooking it up to my car battery and Hyperion charger to charge my spare pack while I trail ride, but I don't want to over discharge the car battery in case it's low. Smart switch to the rescue, same with my RC stuff.

Nice project. I've been thinking about making a similar unit myself with a keyswitch.

A question. It looks like you may be using a latching relay. It is my understanding that physical shock can cause a latching relay to switch. Is that a potential problem here? Hitting a pothole on a bike might turn the power on or off if the board was mounted firmly to the frame in any way?

[K-ray]

I too am intrigued by this simple solution cuz I liike to play with different cell counts
So what would you recommend for cut-off (voltage per cell) for both Lipo and LiFePo4 to keep in the "safe" range?
Thanks
And nice work

[kfong]

For Lipo's I've been using 3.5volts, for Konions 3.3volt and for LifePo4 2.85volts

I too am intrigued by this simple solution cuz I liike to play with different cell counts
So what would you recommend for cut-off (voltage per cell) for both Lipo and LiFePo4 to keep in the "safe" range?
Thanks
And nice work

[docnjoj]

Hey Kenny
Thanks for the response. My Fatpacks have the BMS removed and it is permenently attached to the charger so I charge with the Bosch charger to 6P at about 41volts and about 4 amps. It takes a while to charge but my main problem is the LVC and your switch seems to solve that. When you post programming details that should do it for me in understanding how it works.
otherDoc

[o00scorpion00o]

Hi kfong,

So basically this is like controller lvc, it will switch off or throttle the power based on pack voltage rather than individual cell voltage ?

Can the throttle on off switch be used to switch power on and off to the controller ? that would be very useful.

Motor temp monitoring would be very very convenient , when the new chips become available would we be able to just replace the old one for the new features ?

Also, would you be able to install them in some kind of enclosure ? it would be handy for protecting it when throwing it in a battery bag!


Mark

[kfong]

Yes, it's like the controllers LVC setting. It measures pack voltage and cuts off based on the voltage you determine. But unlike the motor controller, the Smart Switch is a complete power off. No standby current or small battery drain to worry about. It basically protects your battery from ever going too low. Whereas a BMS can still damage a pack due to the constant battery drain even when off, especially if the pack is depleted and sitting around for a while. SImiliar problem if you forget to shut off your ebike. The standby current can take out a drained pack in a few days or less.

The power off switch is just a logic level pin shorted to ground. You would need to see how the throttle on off switch functions to see if it uses similar actions. If it is similiar then they can be paralleled, but this is more for those who are comfortable around electronics.

It will be a while for the new chip to be on line. Apparently my development tools are not up to speed. I have the new chip to play with, but it's useless to me till I find a way to program it. Looking into other compilers at the moment. It would be just replacing the old chip with the new one for the upgraded features. Lack of code space is the only reason I can't offer these features at the moment. I would have to throw out the user interface and have the chip customized to your system to add stuff. For now I think the standard setup has a lot going for it.

There are 4 mounting holes on the board to mount on standoffs. I still have to post more details such as dimension and parts list. Just been busy lately. I might offer a custom CNC enclosure, I need to make one for myself. Really any enclosure would work since the power leads and switches are brought out.

Hi kfong,

So basically this is like controller lvc, it will switch off or throttle the power based on pack voltage rather than individual cell voltage ?

Can the throttle on off switch be used to switch power on and off to the controller ? that would be very useful.

Motor temp monitoring would be very very continent, when the new chips become available would we be able to just replace the old one for the new features ?

Also, would you be able to install them in some kind of enclosure ? it would be handy for protecting it when throwing it in a battery bag!


Mark

[o00scorpion00o]

Hi kfong,

Thank's for the reply, yeah that's all my switch does is short the two pins so that should work fine, it would be cool to have an on off switch without having to pull apart the andersons every time!

If you could build them and install then in an enclosure and have all relevant wires coming out of the box, I think that would be cool!

The motor temp monitoring would get a real interest I'm sure, it would help save a lot of motors from death!

The only problems would be installing the wires through the axle.

Mark