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  1. S

    i2c BMS for hobbyking lipos

    I have been looking at the AD8277 with built in resistors. More expensive but better CMRR then can be achieved with external resistors. Plus gets rid of 24 resistors on the board. Power is 200ua on the amp. I'm going to get the cell monitoring and isolated communications working first. Then ill...
  2. S

    diy bms

    Take a look at my project, fairly similar http://endless-sphere.com/forums/viewtopic.php?f=14&t=61783
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    i2c BMS for hobbyking lipos

    The darlington array is common emitter, and the emitter is tied to same gnd as the mcu. So the base pins will be at the emitter voltage when mcu pins are LOW. The array sinks from the PNP transistors that do the actual cell drain.
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    i2c BMS for hobbyking lipos

    The ULN2003 is just a 7 darlington npn array to reduce part counts. When I pull the pnps to gnd to turn on the cell balancers, the voltage can be up to 25.2v which is too much to sink directly on the atmega. Also I'm using one of the npns to switch the circuit on and off. Theres not much out...
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    i2c BMS for hobbyking lipos

    I think I might ditch the i2c isolation, its just too expensive and parts are hard to come by. Also by not using i2c we can use the atmega328p through hole. I'm going to try a daisy chained serial isolation, as I can do the serial isolation for much cheaper. So how the protocol would work is...
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    i2c BMS for hobbyking lipos

    Looks like the mosfet is a type of FET but with higher impedance. Also it would be nice to use a battery management IC to reduce the resistor count... Unfortunately there is none I can find at a reasonable price. I'm completely open to other solutions rather then the op amps. The celllog 8m...
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    i2c BMS for hobbyking lipos

    Well another problem is the op amp resistors that form the voltage dividers, they cannot be too high of a value or the op amps don't play nice. So there will always be some drain there. Unless the gnd is disconnected, theres going to be at least 0.5ma wasted just by the op amps. I think the...
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    i2c BMS for hobbyking lipos

    Well the real gnd is the negative on the battery, the atmega and opamps are essentially the load for the mosfet. The schematic may be a little confusing with how I have the gnd net. When power is applied to the enable pin, the optocoupler switches the npn to start sinking current to the battery...
  9. S

    i2c BMS for hobbyking lipos

    The gnd is cut by the MMBT2222A-TP NPN transistor should be a almost non-existant leakage (T7). The schematic has the npn where it grounds back to the battery. I can put a timeout on the microcontroller to make sure the bms is always shut down. How this setup would work is one atmega would be...
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    i2c BMS for hobbyking lipos

    Yeah I don't think its going to be that efficient on the power usage. The atmega will probably pull 10ma on its own. And if driving the shunting mosfets its going to need some extra power. So just going to the route of cutting the gnd when not in use so power usage shouldn't matter too much. I...
  11. S

    i2c BMS for hobbyking lipos

    Yeah I was wondering about the input diodes. I'll remove them from the inputs. Maybe I'll put some diodes on the power to allow for lower cell count packs. As far as components, part selection hasn't properly been done. Components were just mostly selected because they were in the eagle...
  12. S

    i2c BMS for hobbyking lipos

    And here is the shunting board schematic. The cell monitor would mount to this board bed of nails style. The shunts are controlled by the output pins of the isolated microcontroller.
  13. S

    i2c BMS for hobbyking lipos

    Here is a rough schematic of the cell monitor board. I still need to calculate a few resistor values, but for the op amp resistors they will be all the same value, around 100k ohm. Also not all parts have been selected yet. So the ICs might change a bit. I am using the atmega644 for prototyping...
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    i2c BMS for hobbyking lipos

    Ok so in search of a easier way to manage lipo batteries, I have decided to design my own bms system. I would like to get a production run done of some nice smd boards. So pretty much looking for how many people would be interested in purchasing. What each board would do is have a read out of...
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    Converting Electric snow blower to battery power

    Another note, the blower seemed have a lot more power on the dc then the ac at 100v. It would probably be sufficient to run at around 50v and the lower voltage would solve a lot of problems.
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    Converting Electric snow blower to battery power

    Alright well here's the update on running the toro 1800. Good news is I've had around 30 hours of solid runtime, and the winter is pretty much over. I was lazy and never put in a fuse. The other day I hit a pair of scissors under the snow and jammed the motor. It was actually completely slient...
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    Converting Electric snow blower to battery power

    I believe the switch is just rated for its ability to break the current, so the ratings should be the same when the switch is closed. Only difference with dc is it has a higher chance of maintaining an arc when the switch is opened. I figure the blower only uses around 3-4amp under no load, so I...
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    Converting Electric snow blower to battery power

    Here you go. I didn't do any modifications to the blower itself. Nothing fancy just 4 batteries in series connected to the plug. I used 14awg of high quality silicone wire. Probably shouldn't go any lower then that. I put a hole in each of the 4 corners of the bag and used zipties. The extra...
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    Converting Electric snow blower to battery power

    Alright I got a power curve 1800 for $50. I wired 4 6s 5000mah zippy batteries from hobbyking in series to get 100v hot off the charger. I attached the pack to a female extention cord end I bought for $5 I plugged it directly into the regular blower plug. Works great, I've run it for around 45...
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