Controller

General BVS related area
JimC
Posts: 11
Joined: Tue May 26, 2009 9:14 pm
Contact:

Controller

Postby JimC » Wed May 27, 2009 11:06 am

I want to build a multi small motor engine so I will need quite a few controllers. Good quality controllers can cost as much or more than the DC brushless motor itself so I have decided to build my own controllers which gives me the advantage of customising the complete package of controllers in one or two packages.

A quick trawl of RS reveals significant savings in buying in quantities of one hundred which is considerably more than I need so I propose that we form a merry band of like minded individuals, agree on a design and which products to buy. We should concentrate on the more expensive components including the more expensive discrete components recommended by the controller manufacturer. Things like 10% tolerance resistors, standard capacitors can be left to the individual as only they can decide which features of the controller they want to enable.

If I get a good response I will get in touch with the wholesaler or manufacturer to get the best possible price, but in any event RS will give us a good idea of the maximum costs.

User avatar
Jeremy
Posts: 472
Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Wed May 27, 2009 12:30 pm

Have you looked at the cheap ebike controllers? I'm using one that cost just $22 and have found that it drives a TowerPro 5330-10T motor very well indeed. All I needed to do was fit Hall sensors to the motor. As a bonus, this controller is software programmable, and is also available in a very high current version.

I have also bought two of the high current versions, without the power FETs (as I wanted to fit my own decent quality ones). Two 18 FET controllers, supplied as populated circuit boards (less FETs), all metalwork, heatsinks, mounting hardware etc, but no external wiring, cost me $130 US, including postage from China. If you were to buy more than two, then I would expect the postage cost to be a bit lower.

Worth considering, as these 18 FET controller are good for up to about 100 amps (battery current) at up to around 100V.

Jeremy

JimC
Posts: 11
Joined: Tue May 26, 2009 9:14 pm
Contact:

Postby JimC » Wed May 27, 2009 1:38 pm

Hi Jeremy,

I am so honoured to rx my first post on the forum from yourself. I have read quite a few of your posts and I like your style.

What you said is interesting can you post links.

I am thinking about controller:

http://uk.rs-online.com/web/search/sear ... &R=2269891

£7.91 each or £5.83 each on an order of 100

and MOSFET :

http://uk.rs-online.com/web/search/sear ... &R=0193464

1 of £23.26 and when ordering 50 at £11.93 each..

I am not suggesting buying the units from RS as I can probably get a better deal elsewhere. Of course this bulk buying is only applicable when the design has already been finalised and bench tested.

Back in the bad old days when I still working for a living (had my own business, Sat Telecoms and IT infrastructure for the Petrochem industry) I went to the 2007 Computex show in Taipei as a buyer and the prices of good quality IT equipment was astounding. So I will definitely be looking at manufacturers and dealers in Taiwan as a possible source.

Best
JimC

User avatar
Jeremy
Posts: 472
Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Wed May 27, 2009 5:11 pm

Jim,

Thanks for the kind words.

The cheapest 6 FET controller is this one: http://tinyurl.com/p7va2p supplied by a chap called Keywin Ge in China. Keywin will supply the bigger 18 FET controller directly if you email him, he just sends a PayPal invoice to you by email.

There is a great deal of information on these controllers on the Endless Sphere forum. Some useful threads to take a look at are:

http://endless-sphere.com/forums/viewto ... f=2&t=5713 created by the original US importer for these controllers, who has a fairly "interesting" approach to trying to understand the technology.

http://endless-sphere.com/forums/viewto ... =2&t=10312 created by a chap who, like me, has bought populated circuit boards etc from Keywin Ge. This chap is building and selling high power, custom built, controllers in the US, using the Keywin parts as a base.

http://endless-sphere.com/forums/viewto ... f=2&t=8610 was a thread started to try and collate all the information on these controllers into one place.

This thread: http://endless-sphere.com/forums/viewto ... =28&t=9061 has some useful information on fitting Hall sensors to brushless motors, including the work I did in developing my motor modification.

There's a great deal of useful information in these links, but it is buried in some fairly poorly informed comment at times. Hopefully you may find it useful.

That FET you've selected is quite a high loss device, as it has an Rdson of 33mohms. The IRFB3077 FETs I'm using in my modified $22 controller have an Rdson of only 3.3mohms maximum, yet will handle 210A at 75V. As these big RC brushless motors have a fairly high kV (typically around 130 to 150) they seldom tolerate voltages of above about 70V or so without running beyond their safe rpm level.

A very popular FET for these controllers is the IRFB4110, which allows voltages up to around 100V to be used, yet will still handle around 100 amps or so per device (depending on version - some are package limited to 70A). It has a higher Rdson of around 5.6mohm, but this is still OK for the sort of power levels these motors are likely to operate at.

Hope all this helps a bit.

Jeremy

JimC
Posts: 11
Joined: Tue May 26, 2009 9:14 pm
Contact:

Postby JimC » Sat May 30, 2009 9:04 am

Jeremy,

Thanks for all that I have had a couple of days making decisions.

For the controller I am going with the 18 FET one you mentioned and just as you did they will be unpopulated so I can fit my own choice of FETs. I will order 4 of these as I definitely need 2 for my project and my next project (a 20' cabin cruiser will need two). Out of the box this controller does everything I need but I note that there are unused features which I might enable in the fullness of time. Using the regen is a strong possibility.

I will get 100 FETs which is slightly more than I need but by buying in bulk I will end up with 100 Fets for the cost of buying 80 and leaves me with plenty of spares. I have never used FETs before so I have started researching there use and ordered a couple of books from the library so it will be some weeks before I am ready to order them.

I have the motors down to a choice of two.

When I have made my final decisions I will let you know.

Best
JimC

User avatar
Jeremy
Posts: 472
Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Sat May 30, 2009 10:37 am

Glad you've managed to wade through all of that stuff and make a decision, Jim, it can be hard going at times!

The choice of FETs is fairly limited, particularly when the "hidden" specification limits are looked at. Quite a few older TO220 devices are package limited to a current of around 70 amps, even though the spec quotes a much higher value for Id. Some of the newer devices, like the 75V IRFB3077s that I've opted for, have an improved internal bond wire configuration that increases the continuous safe current to about 120 amps, still only about half the rated Id.

In order of importance, the specification parameters to look out for are:

Vds - at least as high as the highest off load voltage that you think the controller might see, plus a few volts as a safety margin.

Id - at least as high as the maximum phase current that you expect to run at, bearing in mind that the phase current can be several times greater than the battery current.

Rdson - the drain/source on resistance. This needs to be as low as possible, as it has a major impact on device power dissipation and controller losses.

Qg - the total gate charge value. This must be broadly similar to the gate charge for the original FET types used in the controller, as it's critical in determining FET switching speeds. In practice, anything from about 140 to 240 nC is acceptable for these Infineon controllers, more than about 240 nC will probably increase FET switching losses to an unacceptable degree.

Rthetajc - the junction to case thermal resistance. This needs to be no more than about 0.5 deg C/W, as even with a perfect heatsink the junction will still run too hot if you try and run the device at close to it's maximum current rating.

The FETs will automatically share current evenly, so you can assume that the 18 FET controller will have three FETs conducting at any one time, with the current being split fairly evenly between them. The operating limit won't be the current rating of the devices, but will be the temperature of the FET junctions. This is why 18 FETs are needed even for a controller that is rated at perhaps a third or less of the device apparent ratings.

If you are content to operate below 70 volts or so, then I'd opt for the IRFB3077 FETs, as these are about the best about at the moment for this voltage and current. Best value at the 100V point is without doubt the newer package versions of the IRFB4110 (watch out though, as the older version has a lower package current limit of 75A, the newer version is OK for 120A, like the IRFB3077).

There are "fake" FETs around from China that are often sold as IRFB4110s, as these FETs are a very popular upgrade for controllers. They can usually be identified by having incorrect package markings, often they will just have "FB4110" as the part number, with a false International Rectifier "IR" logo elsewhere on the device. The best bet is to buy from a well-respected supplier, like RS, Farnell or Digikey (I've found the latter to be very good, often slightly cheaper than RS or Farnell). Digikey are now based in the UK, as well as the US, which makes them easier to deal with for us.

These Infineon controllers have got a lot of extra features built in, but not well documented. There are two forms of emergency power-off, one operated by a wire going low, one by a wire going high, so that the controller can be turned off with either a traditional hand-brake type switch that switches to ground, or by a brake light switch that switches to the supply. There is a regen capability built in, that is turned on or off with another wire. Throttle control can be either a 0 - 5V signal, or a set of three speed wires that connect to a simple selector switch, with the speeds being programmed via the PC serial interface. Reverse is selected by taking another wire low, with the maximum reverse speed being set via the PC interface (default is 33%). The current limit is set by default on the 18 FET version to 45 amps (battery current) but this can be adjusted in the programming software, as can the maximum phase current. Current limiting is achieved via an internal shunt on the ground return battery feed, that feeds a small voltage that's proportional to current into an A to D converter on the microcontroller.

All told I'm quite staggered at how much functionality there is in these units for the price. The small 6 FET version that I've been experimenting with has exactly the same programming capability as the 18 FET version, yet costs just $22 ready built and is little larger than a packet of cigarettes!

Hope all this stuff helps, rather than confuses! BTW, if you are ordering a lot of FETs, then depending on your choice I may well be interested in some, if you don't mind adding a few more to your order. Obviously I'd cover the additional costs, postage etc. At the moment, I'm leaning towards using some more IRFB3077 FETs, so would be interested in about 40 of these if they were your chosen device.

Jeremy

JimC
Posts: 11
Joined: Tue May 26, 2009 9:14 pm
Contact:

Postby JimC » Sat May 30, 2009 4:31 pm

I would be perfectly happy using the FETs as yourself. When do you need them? I cannot afford to buy the FET's and the controllers at the same time but I am perfectly happy getting the FETs first. Ging to the dealer with an order of 140 FETs has got be worth a reasonable discount.

I am glad that you mentioned the RDSON issues as for the life of me I could not work out why the value should be <5Mohm but I didn't want ask as it would have been good practice to work it out myself but I still have some work here to work out exactly why.

BTW the project I am working on now is a town quad bike. I am looking for a minimum range of 40 miles and a minimum speed of 40 mph. I think these figures are attainable and are suitable for town work.

JimC
Posts: 11
Joined: Tue May 26, 2009 9:14 pm
Contact:

Postby JimC » Sat May 30, 2009 9:47 pm

Hi Jeremy,

The best price for the IRFB3077PBF that I could find was based on an order of 150 (they come in packs of 50) from International Rectifiers themselves. There's a surprise.

US$2.4 each
150 for $360
Shipping to UK $50.20
Total $410.20

That is not too shabby at all. I was ordering as a guest and the site did say that registered users got enhanced prices so if you want to go for them I will register first and the price might come down slightly.

Best
JimC

User avatar
Jeremy
Posts: 472
Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Sun May 31, 2009 8:40 am

Jim,

The snag with buying direct from IR in the US is that there is a fairly good chance that the package will attract import duty, VAT and the inevitable "handling fee". In my experience, the latter is usually around £15 to £20 per consignment, charged in the UK by the courier before release of the goods. This makes the total cost of buying 150 FETs from IR about:

£253.98 for the FETs and shipping
£25.40 import duty
£38.10 VAT
£15 handling fee

So a total of around £332.48, or about £2.22 each

The unit price from Digikey is £1.9544 plus VAT for quantities over 100, with free shipping, which works out at £2.25 each, but that price is for any quantity between 100 and 250, so we can have just the number we need.

Assuming that you want 72 FETs plus a few spares, maybe 80 FETs in total, and that I want 40 FETs (36 plus 4 spares) then an order for 120 IRFB3077s from Digikey would come to £234.53 plus VAT, or £269.71 inc VAT.

Overall, this may be a better bet than buying direct from IR, although if we get lucky and the IR delivery arrives without being charged for duty, VAT and the handling fee this might not be the case!

I'm in no hurry for the FETs, as I'm going to be experimenting with my 6 FET controller for a few more weeks before I get around to building my two 18 FET controller boards. If you want to go ahead and order the controllers first, then please do. I'm quite happy to buy the FETs and let you have yours when you're ready for them, if that would be easier.

Be aware that Keywin Ge can be a bit slow to answer emails, you sometimes have to email him again as a reminder! With luck, you should get four controllers, without FETs, for around $250 or so, maybe £155. My guess is that you won't get charged duty or VAT, as Keywin usually ships these packages marked as "gift" or "sample"!

Jeremy

JimC
Posts: 11
Joined: Tue May 26, 2009 9:14 pm
Contact:

Postby JimC » Sun May 31, 2009 11:20 am

Already thought of import etc, but I didn't have the costs. I can have IR ship to a friend in the states then have my friend post them here.

I dont mind having up to 2 times as many FET's as I need because I may end up having 3 or 4 motors in the quad and back of a fag packet calc for the cabin cruiser indicate a minimum of 4 motors for slow cruising, about 4 or 5 knots.


Return to “General”

Who is online

Users browsing this forum: No registered users and 9 guests