Search found 103 matches

by bobc
Tue Apr 19, 2011 12:27 pm
Forum: All things battery related
Topic: BMS Basic understanding
Replies: 3
Views: 7429

Re: BMS Basic understanding

Charging is filling the battery with electricity - equalising is making sure each of the cells which make up the battery is at the same state of charge. I don't know what batteries are in the Gwiz but if they're normal lead acid wet cells, they come in blocks of 6 cells (giving a 12V battery) and yo...
by bobc
Wed Feb 16, 2011 12:08 am
Forum: All things battery related
Topic: Experiment with li- poly batteries in a greenpower racecar
Replies: 16
Views: 16902

Re: Experiment with li- poly batteries in a greenpower racec

Here's the charging system I've come up with for the car: basically a fair number of these boxes each of which will charge 6 single cells with 3A. Each charger PCB is on an isolated secondary on the transformer, each has its own bridge rectifier. So I can wire 'em up any old way without causing smok...
by bobc
Thu Jan 27, 2011 11:35 pm
Forum: Electrically assisted bikes
Topic: I just made an electrically assisted bike conversion......
Replies: 8
Views: 16720

Re: I just made an electrically assisted bike conversion....

Sounds as though the karting gear is pretty good value too. Last weekend it was run on 2 off 20C 2.2Ah 3S lipoly cells (i.e. about 22V), I think Matt's buying some 5Ah cells to give him (with luck) enough range - he has 2 big hills to climb so we'll see, I suspect he'll have to double up again.
by bobc
Tue Jan 25, 2011 2:04 pm
Forum: Electrically assisted bikes
Topic: I just made an electrically assisted bike conversion......
Replies: 8
Views: 16720

Re: I just made an electrically assisted bike conversion......

as an aside - some back of envelope calulations of the torque capability of the taperlock fixing: motor 3500W @ 8000rpm - 8000rpm is 840rad/s so motor torque is 4.1Nm M3 screws - say root diameter 2.5mm; stainless steel say 200N/mm^2 stress for 0.2% - that's 982N per screw - there are 4 so that's 39...
by bobc
Tue Jan 25, 2011 1:13 pm
Forum: Electrically assisted bikes
Topic: I just made an electrically assisted bike conversion......
Replies: 8
Views: 16720

Re: I just made an electrically assisted bike conversion......

No I didn't like the grubscrews much either - part of the problem with them is that the shaft is about as hard as the grubscrew. I get a good deal with the local laser cutters - they've made all sorts of bit for me now, 1st name terms & I always give them cash, but equally I know they're not giv...
by bobc
Mon Jan 24, 2011 11:35 pm
Forum: Electrically assisted bikes
Topic: I just made an electrically assisted bike conversion......
Replies: 8
Views: 16720

I just made an electrically assisted bike conversion......

Basically just using up RC gear I had lying around from other projects. I'll post a couple of pictures on the off-chance that someone might find some useful ideas among the insanity.... I've only run it with a small battery pack, but it actually behaved perfectly, straight out of the box - ran for a...
by bobc
Mon Jan 24, 2011 11:11 pm
Forum: All things battery related
Topic: Li-poly batteries - incendiary device look out!!
Replies: 8
Views: 9271

Re: Li-poly batteries - incendiary device look out!!

I ordered another twist grip - I did actually dismantle the first one to see what was in it, which might explain if its performance is not as originally designed! I've also ordered one of the $14 8S lipo voltage monitors from hobby city - it has an alarm output which I can use to kill the drive. I'l...
by bobc
Sun Jan 23, 2011 4:16 pm
Forum: All things battery related
Topic: Li-poly batteries - incendiary device look out!!
Replies: 8
Views: 9271

Re: Li-poly batteries - incendiary device look out!!

yeah an audio warning could be practical - still needs the driver to react appropriately though - & its an easy job to have the controller cut the demand on the servo output. Also something that looks at every cell sounds good (anything just looking at total volts won't do that) The twist grip t...
by bobc
Sun Jan 23, 2011 12:59 pm
Forum: All things battery related
Topic: Li-poly batteries - incendiary device look out!!
Replies: 8
Views: 9271

Re: Li-poly batteries - incendiary device look out!!

I was keen to give a battery some serious abuse because I'm going to have a LOT of them in the landspeed record car & I need to know the risks/hazards and develop suitable strategies. I do feel somewhat less worried about the battery/fireball issue now but will carry on with the tests ;^) We had...
by bobc
Sat Jan 22, 2011 10:12 pm
Forum: All things battery related
Topic: Li-poly batteries - incendiary device look out!!
Replies: 8
Views: 9271

Li-poly batteries - incendiary device look out!!

OK the actual post is nothing like so inflammatory as the title... I got my ebike project mobile today http://i543.photobucket.com/albums/gg471/bobc0/bikebits/bike004.jpg The cheap 40A ESC turned out NOT to have undervoltage protection & I discharged a 3S lipoly to 6.5V. Oops The side was quite ...

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