Need info about protection diode across keyed switch.

[Frostypepper]

Hi everyone, Im new to the forums and new to ebikes in general. Certainly glad I found this forum.

Long story short I'm converting a 3 wheel bike to a electric bike with a MagicPie3 for my ailing mother. I am going with a 48 volt system and have most of the parts and things hammered out.

What I would like to do is add a heavy diode (directed from mp3 to battery) basically across the switch and possibly fuse to prevent damage to the motor if the fuse popped or switch failed and regenerative braking took place over a distance. I have a 48 volt common keyed switch used for golf carts, and a standard inline fuse holder that I would install as close to the battery as possible.

Would this stud diode http://www.amazon.com/Amp-Volt-Stud-Blocking-Diode/dp/B0056RH3P2/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1405800008&sr=1-1-catcorr&keywords=40+amp+diode serve my purpose? I am simply trying to add some protection to the motor.

Are there any other components that I can possibly add to add to the protection and longevity of the Magic Pie 3?

The mp3 will be front mounted with cantilever brakes, the battery pack is 4 x 12volt 10.5Ah sealed glass mat batteries. The 3 wheeled bike is a modified trail master.

Thanks for the help.

-Pat

[Frostypepper]

Nobody has used or made any sort of back flow protection for their motor? Any information or pointing me in the right direction would be appreciated.

[Frostypepper]

bump

[Morgen 3Eman]

Hi Pat,

Since you seem to want some reply, here goes.

Why do it?

Read C) first... I'm too lazy to change the list..

A)  If the fuse is going to blow, it will be under a high current condition, which implies hard acceleration, which implies low speed.  At low speed the regen voltage would be low, and probably not damaging to the motor.   

B)  Unless your Mom is a crazy old bu!*ar like me, she won't be going terribly fast anyway.  Again, low regen voltage  would be generated.  By the way, does she know how easy it is to tip over a trike while turning?   You should warn her....

C)  Fuse values are generally picked to protect the circuitry from failure mode current levels.  If the fuse blows, it implies there has been a failure already.  The diode will be in the circuit to protect what?  The failed motor/controller/wiring/what ever caused the fuse to blow?

You should not put a 30 amp fuse in a circuit you expect to draw 30 amps during normal operation.

D)  Tell her to have fun.

Sincerely,
Dennis

[Bikemad]

Hi Pat andto the forum.

I don't think you need to worry too much about a diode across the battery switch as the controller seems to sink all the regen braking energy through itself at low speeds and does not actually send anything back into the battery until you're travelling faster than ~10mph.

I recently fitted a larger 50 tooth chainwheel on my bike and tested it down the road without putting a battery pack on the bike, just to see how much higher the gearing was. It seems that the later GM controllers have a different Regenerative/Electronic Braking System to the earlier ones, as the motor's strong braking effect actually cut in when I braked from a high speed, even without a battery being connected!

I went for a 3.5 mile ride yesterday with the dog and connected a pair of watt meters so I could monitor the current flow in both directions.
I was rather disappointed to find out just how low the regen measurements were on the watt meter. I had actually used 2.162Ah from the battery, but regenerative braking had only put back 0.010Ah (0.46%) after I had ridden down a long steep hill using only regen to maintain ~7mph because the dog simply refused to go any faster.

I must therefore assume that the majority of the low speed braking energy is simply being wasted, as the maximum regen current was only 3.67 amps (98.1 watts) and this included braking to a standstill from at least 15mph at the end of the trip.

The dynamic braking effect with the later controller seems to remain more effective down to a much lower speed than it did with the earlier controllers, but this appears to be very inefficient as it is wasting a great deal of the available kinetic energy.

Are there any other components that I can possibly add to add to the protection and longevity of the Magic Pie III?

The only thing that I can suggest is to make sure you use torque arms on the front axle to prevent the axle from spinning inside the fork dropouts. If the axle spins, the motor wiring harness will become damaged and the front wheel can also come detached from the forks.

Alan

[Frostypepper]

Thanks for the advice guys, I was going to use the diode to prevent the motor from burning its controller out if the switch failed or was turned off during use and regenerative breaking caused a build up. But I guess perhaps I may be over complicating things.

Morgen Eman (love the name), I do plan on using at least 1.5 times the normal usage amperage for my fuse. Thanks for the advice.

Bikemad, I believe I may just forgo the diode. Again I think I may be over complicating the issue. I just wanted to make sure my mother got out and about and got stuck somewhere.

Thanks so much for the help!

[Bikemad]

I just wanted to make sure my mother got out and about and got stuck somewhere.

That's really cruel, mean and spiteful! I can't understand how anyone could do such an awful thing to their own mother, it just makes me so angry even thinking about it.


I am so disappointed in you.

   

Alan
 

[Frostypepper]

I just wanted to make sure my mother got out and about and got stuck somewhere.

DIDNT, I meant so she didnt get stuck somewhere!

Typing is hard.