Motor Controller, H Bridge or System On A Chip? - Page 1
Forum section: electronics / beginners

author: tornup
author_rank: Newbie
timestamp: April 14, 2014, 02:54:04 pm
content: Hi All,Long time no post, will jump straight to the point.I have 2x 24V motors(off a wheelchair) which i plan to build a controller for.... their heavy duty motors which will be powering an electric kids car(containing 2 kids) so there may be some large current draws happening(I’m not sure on figures ATM but I expect stall currents of about 30ish amps....)I tore down the speed controller, and the "heavy duty" bit is using the following:BUZ111S Mosfets all N-ChannelIR2110(discontinued I think...) High/low side N channel driver.This gives an upper limit of about 80A(“Id” of 80A on the mosfets)This originally was the route I was going to go down, i was going to build a circuit with the IR2110 and some spec’ed out Mosfet. However the replacement to the IR2110 which is the IRS2110 quotes gate drive supply range from 10v to 20v, now i was under the impression that to drive a high side mosfet at 24 volts the gate needs to be higher than the drain? So this replacement won’t meet me requirements? Please correct me if i am wrong, i am very new to all of this, but eager to learn!The other plan i have is to use a BTN7960B..https://www.infineon.com/cms/en/product/power/motor-driver/integrated-half-bridge-driver/BTN7960B/productType.html?productType=db3a304413719f72011372e9554e00daWhich is actually used on the following:https://www.jameco.com/Jameco/Products/ProdDS/2128534UsersManual.pdfThis has a supply voltage within my spec(max supply V = 45V)And according to the specification sheet for the megamoto(linked above) the following current specs:13A cont. at 100% duty cycle12A cont. at 70%30A - 5 second peakMy concerns are around the peak current being a tad low should my kids decide to drive forward with the car up against a wall(motors stalled)(I have an impact detection idea I plan to implement into the design preventing this, however I cant cater for every variable and want to ensure the current limits are in spec )My main question is, is the BTN7960B out of spec? Has anyone had any experience with working with one of these? I feel like I am overlooking something, considering iv gone from a motor controller with 8 heavy duty mosfets with 4 drivers to 4x System on chip solution....Id loves your feedback on all of this! As I mentioned I am quite new to all of this so bear with me, but I have got a bit sick of reading/watching videos and I want to try/fail at a few things to further my learning, and what better a project then an electric car for my kids!? (famous last words right there!!)Thanks,Tom.

author: senso
author_rank: Frequent Contributor
timestamp: April 14, 2014, 03:58:21 pm
content: I have a dual H bridge removed from an electric wheel chair, if you want I can snap some photos and ID the major chips involved in the h-bridge.

author: tornup
author_rank: Newbie
timestamp: April 14, 2014, 06:26:49 pm
content: Quote from: senso on April 14, 2014, 03:58:21 pmSenso, That would be really helpful! only if you don't mind though!!I have just read this document:http://www.irf.com/technical-info/appnotes/an-1100.pdfIt details the difference between the IRS211(0,3) and IR211(0,3) with the IRS2110 being the recommended "pin to pin compatible replacement" to the IR2110.... I think i am reading it correctly, actually, re-reading it... I am confused.....What do they mean by "High side floating supply voltage"(which is rated at 520v) does that mean if iv got 24v over the mosfet on the high side, and i need to go 10V higher on the gate this chip will facilitate that?and I presume applying 20V to the low side mosfet will allow it to be "fully open"?This is what i am basing my design on, it is using the older IR2110.http://2.bp.blogspot.com/-dlEcbNapBZ0/UPvnk7y2MuI/AAAAAAAAAZ4/bfSogInXgj4/s1600/IR2110+-+3.pngAlso the speed controller i tore down had a 74HC14 in it, the NXP website states the following:The 74HC14; 74HCT14 provides six inverting buffers with Schmitt-trigger action. It is capable of transforming slowly changing input signals into sharply defined, jitter-free output signals.Could someone detail a little more what this is used for? and if it is a component i should also be considering including in my design.Or, should I shift my focus to some System on a chip solution like the previously mentioned BTN7960B?Thanks,Tom.

author: johansen
author_rank: Super Contributor
timestamp: April 15, 2014, 05:35:09 am
content: if that BTN7960B is fairly cheap then i would use it.be sure and solder it to a block of copper and then heatsink that to your chassis or whatever.note however there is a better method.. a dpdt relay and a single, low side mosfet. you can get creative and use the mosfet resistance to sense the current or you can use a low side current sense resistor.

author: tornup
author_rank: Newbie
timestamp: April 15, 2014, 08:30:52 am
content: Quote from: johansen on April 15, 2014, 05:35:09 amI am Tempted to use it, my concern was the max current rating, im concerned my motors will draw more current when stalled then the component is capable of.... iv not worked with DC motors of this size before, does anyone have any tips on how i can calculate the max current draw of the motors better then i am at present(which consists of educated guess's and pulling numbers out of a top hat! lol)Quote from: johansen on April 15, 2014, 05:35:09 amthe thought crossed my mind, however i was under the assumption I couldn't apply PWM to make the motors speed controllable by using a relay?Would a high current Solid State Relay allow PWM??Quote from: johansen on April 15, 2014, 05:35:09 amI am slightly confused, surly if i am measuring the resistance of the mosfet it is just going to tell me how much the magnetic coil of the relay is drawing, not the motors?Thanks for your help!Tom.

author: Kremmen
author_rank: Super Contributor
timestamp: April 15, 2014, 12:31:35 pm
content: I think you misunderstand the relay idea a bit. Let me try to explain:1. Connect the supply to a DPDT power relay such that when connecting the motor between the common terminals, in one position of the relay the supply voltage is "direct" and in the other "reversed.2. connect the remaining relay contacts to ground via the power MOSFET.3. Now the relay controls the motor direction (it not pwm controlled, you just energize it for one direction and let go for the other.4. All pwm is done by the MOSFETSo you have 2 signals - relay control for direction and MOSFET pwm for speed. To change direction you just switch the relay on or off. Whether you should do this while the motor is turnming is another thing and depends on how the rest of the circuit is implemented.You might want to use another small MOSFET to drive the relay coil, of course.

author: tornup
author_rank: Newbie
timestamp: August 08, 2014, 05:45:55 pm
content: Hi All,First of all apologies in reigniting an old thread, however my question remain the same so i thought it best not to create an identical post.I am starting to spec out this project and have come across a new IC/Mosfet/Driver, its part number is: BTS50055-1TMBdatasheet:http://www.farnell.com/datasheets/1651319.pdfWhat it looks like is an IC with TTL control levels and massive current driving capacity. ideal for what i need(The motors I am driving peak at about 8-9 Amps when partially stalled(its hard to full stall them without building a specialist rig!)I was wondering if anyone has used this before? What are your views in using these as a motor driver?The only downfall is their price(£5.92 each) and the requirement for 8 (2 H Bridge configurations) meaning a total of £48 in just driver ICs.......would love to hear your views!Thanks,Torn!