Need Safety tips for large motors/batteries/capacitors

At 32 amps draw, 210,000 uf will do nothing for you. As a point of information, when using caps like those you always want to use a voltage _lower_ than the cap is rated. Exposing them to a voltage higher than their rating is something to avoid.

Regarding using diodes to isolate the batteries - bridges are not required. I would use the diodes, regardless of which type of batteries you use. You can use a single diode for each series battery setup, like this:

+--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+ | | +--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+---> + | +-------------------------------------------------------> -

You need a different charging algorithm depending on battery chemistry - you don't want to charge NiMh, Lead Acid and Lithium with the same charger, unless it is programmable for those types. Otherwise, you need a separate charger for each chemistry.

Ed

I just looked at some battery management ICs on websites for TI, Linear Technology, and Maxim. They are a little pricey but may be worthwhile for a high end application. The big picture seems to be Li-Ion, but they have multichemistry chargers and some that are programmable and integrate a "fuel gage". They have switching type chargers up to about 4 amps in single IC packages. I have decided to try to roll my own using a PIC.

Energy storage for the capacitors is based on 1/2*C*V^2, so your 210,000 uF

25 V bank will store 65 J (watt-seconds). If you have 800 watts of motors (1 HP), the energy will power the vehicle for less than 0.1 seconds. They are most useful for quick energy dumps from dynamic braking, but you will need more than that to absorb the kinetic energy of a fast stop. Supercapacitors are available, such as Maxwell BPAP1200 ? E270, which are 1200 F at 2.7 V. Ten in series gives you 120 F at 27 volts, and energy storage of 43,000 W-Sec, or 50 seconds run time at 800 watts. They cost about $46 each.

You might do best with two independent systems so you don't need to parallel the batteries. You should be able to connect the controllers so they synchronize motor speed, and you probably want to have a speed differential for turning.

For any high power circuitry, it is a good idea to have it enclosed in a rugged electrical box, and wear eye protection when testing. Judicious use of fuses and other current limiting devices is also advised.

Good luck,

Paul

Hope my well what? :)

Seriously, have a look at this

and Yahoo groups for relevant interests. The power assist group is knowledgeable about batteries controllers and motors for bicycles. Then there are scooter parts houses for cheap Chinese motors, controllers and batteries. There is one in Australia called Oatley Electronics at

jack

Thats awesome, thanks for the advice. Ok, so when I get around to buying li-poly batteries, I was really planning on buying a nice charger for it, cause they have expensive and I dont want to screw them up, so the multi chemistry charger is not really an issue, thanks for the advice tho.

For the lead acid batteries they are fairly simple to charge from what ive seen, so I want to whip up a charger for them. I see the wisdom of seperating the circuits to keep the batteries seperate, Ground from the 2 circuits should be tied together tho, correct?

Now the motors I have a geared down to 260 or so RPM's, with a worm gear reduction. This does not allow for free wheeling, so energy storage from braking is not such an issue, as the mechanical segment has to soak up any excess energy during braking.

The super caps are interesting, especially since I have been reading about these fantastical claims from eestor in texas, do you have any resources on charging them? I was just under the impression that all motor driver circuits require big caps in parallel with the motors, for acceleration from a dead start, should I not put them in the circuit? What would be the optimal capacitor arrangement for gearmotors?

As for fuses and current limiting devices, what sort of thing would be best? I am most concerned with shorts, so a fuse for about 40 amps would probably do the trick. Gotta check for DC breakers, hmmm.

Do you happen to know the code for 15 amp diodes? Are those still of the 1N4*** series? Also, I think in the end I am going to put all teh motor circuitry in an enclosed oil filled box for extra robustness and heat dissipitation, so I dont need to massively over design all the parameters, when i was in school I saw a 1N4002 take 8 amps for over

20 minutes by being enclosed in a barrel of oil.

Sorry for all the annoying questions, just with the last motorized vehicle I attempted to build I blew all sorts of hip4080's and the busbar for all my caps melted and a variety of other silly mishaps that I would like to avoid this time.

Thanks a ton

-Coleston

at

Thanks alot man, that first link is extremely helpful. Learned a ton. :)

[snip]

Probably a good idea, and should be bonded to chassis.

You need to look at the surge current requirements for the motors and the capacity of the batteries. The capacitors can help reduce high current surges through the batteries, as well as a lower ESR to keep voltage steady.

Many AC breakers are also rated for DC use, but inductive loads can be a real problem if snubbers or freewheeling diodes are not installed (or are defective). Sometimes two or three poles are hooked in series to get higher DC rating. Fuses are ultimately more fail-safe, but expensive and cumbersome to replace. Fast blow and even high speed semiconductor fuses are probably best for DC. It's probably a good idea to put a fuse on the positive terminal of each large capacitor if they are in parallel. Ordinary

250 volt or 600 volt fuses at 40 amps should not be too expensive. I bought a lot of DC rated high current breakers surplus on eBay for a couple bucks each. If you need a few I'll get more details on them if it's worthwhile to ship some (from 21030). My company designs and builds breaker test sets, so I can check them out.

I think the oil filled box would be more trouble than it's worth, and possibly dangerous. Just a strong steel NEMA type enclosure should be fine for blast containment. If anything, you might consider filling it with very clean sand.

Sounds like my kind of fun!

Paul