Questions about fuses, key switches and relays

[Abe]

Hello Alan,
I would like to find out a number of issues related to the battery connection (Motor Magic Pi 4 750W The Battery is  48v 15a):
1. I would like to add a fuse between the battery and the motor, what size fuse and what kind (Slow blow)?
2. I can use UNIVERSAL KEY IGNITION SWITCH without relay?
3. It is better to add a relay capable of 40a flow?
** What are your recommendations from your experience.
Thank you,
Ave

[Bikemad]

1. I would like to add a fuse between the battery and the motor, what size fuse and what kind (Slow blow)?

I use automotive miniature blade type fuses on my battery packs, but you need to be careful not to overload the fuse holder as this can lead to arcing of the fuse contact pins which generates a lot of heat and can melt the plastic casing of the fuse:



This happened because I was regularly using between 40 and 50 Amps for short bursts through this fuse holder (which I later found out was only rated for 30 Amps):



I solved the contact problem (and the occasional fuse blowing) by making up an 80 Amp fuse (2 x 40 Amp fuses in parallel with soldered connections):



This has been working nicely since it was fitted with no further problem whatsoever.
The 80 Amp fuse is really a bit too large for the 50 Amps maximum that I and currently using, but it's got to be a lot better than no fuse. A 60 Amp fuse (2 x 30 Amp fuses in parallel) would have been more than sufficient but I basically used the 40 Amp fuses because I already had them.

2. I can use UNIVERSAL KEY IGNITION SWITCH without relay?

If the switch is the same as the GM key switch it should cope with the 30 Amps maximum that your Magic Pie requires and will be OK to use without a relay, but if it is rated a lot less than 30 Amps it will probably burn the switch contacts without a relay.

3. It is better to add a relay capable of 40a flow?

If you use a relay it will ensure that the key switch will not be overloaded, but you would need a 48V relay and the relay coil will then draw a small (but continual) amount of current from the battery all the time it is energised.

Trying to find a cheap 48V relay that can handle enough current for the Magic Pie may not be easy, this is why I came up with this easy solution for a DIY 48V relay that could handle very high current:



Other options include the use of a heavy duty battery isolator key switch or a latching relay which won't consume any power while turned on or off, although the latching relay still requires a short pulse of power to switch from one state to the other.

Alan
 

[Lewis Balentine]

FYI:
http://www.texasindustrialelectric.com/relays.asp
T9APD52-48-01 5-1419102-8
48 Volt 30 Amp
$11.50

Also check out relays for golf carts/ Club cars. They work on 48 volts but I have not found anything regarding the current ratings.
Example:
part :  1018070-01
http://beavergolfcartparts.com/solenoid48volt4terminal.aspx

Starter solenoids have to handle making and breaking the circuit under load. That is EXTREMELY punishing. People have been known to make emergency welds using 12 volt batteries and jumper cables. Making and breaking the circuit without a load and then carrying the current is not nearly so destructive elsewise those little 10 and 12 gauge wires would vaporize.

[Hastings]

regarding fuses I have switched to maxi automotive fuses  because the holder is rated at 60-90 A  as I had the same experience with overheating  of the fuse connectors without blowing the fuse =30 A

[Abe]

Hello Alan,
I took myself a little time to study the issue of the fuse, I think I found a solution and I wanted to hear what you think?
1. Car Audio Waterproof Mini ANL 60A Fuse (see attachment).
2. ** Such fuse can hold up to 2500 Watt.
3. Soild State Relay SSR-40 DD DC To DC 3-32V 40A 5-80V (see attachment).
4. ** Is 40 amp relay can keep the flow of 48v 750w motors?.

Thank you,
Abe

[Bikemad]

Hi Abe,

Solid state relays generate heat during use and will also continually draw a small amount of current from the battery when switched off.
Although 2mA is not very much, it will still drain 1.5Ah per month out of your battery if left connected but unused over the winter months etc.

I suggest you read this post about solid state relays before you purchase one.

The advert on Amazon for that relay clearly states:

Note: A heatsink must be used or it will get burned out.

The required heatsink is very large in comparison to the compact relay and would also require adequate ventilation and probably a cooling fan if constant high current is likely to be used.

The T9APD52-48-01 5-1419102-8 48 Volt 30 Amp relay that Lewis mentioned in his earlier post would be a much more sensible option. The 1 Watt coil would only consume about 0.020 Amp (20mA) which is not too bad for a standard relay, and it might even be less than the solid state relay.

Alan
 

[Abe]

Hello Alan,
I'm usual happy to hear their opinion, usually your tips always help.

** I hope that you have knowledge of mechanical, recently I purchased Avid BB7 Mechanical Disc Brake, I having a problem, unfortunately, is not indicated on the set which belongs to the rear wheel and which to the front wheel.
However there is marking the one sets IS 20MM, and other IS 0MM, what does it mean?

Thanks,
Avi

[Bikemad]

If you have 160mm diameter discs front and rear the IS 0MM should be for the front brake and the IS 20MM for the rear.


Alan