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)
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.
- Ignore the SMT resistors seen, I'm better stocked on SMT parts so I used them.
- smart switch top 2.jpg (55.94 KiB) Viewed 21740 times
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- sw PCB top.jpg (54.63 KiB) Viewed 21738 times
- sw PCB bot.jpg (43.39 KiB) Viewed 21738 times
- Serial interface top.jpg (42.33 KiB) Viewed 21522 times
- Serial interface bottom.jpg (31.75 KiB) Viewed 21522 times
Last edited by kfong
on Feb 27, 2013 8:21 pm, edited 34 times in total.