Electric Go Kart Conversion

[Webie1]

Hey guys,

I'm part of a Queen's University team attempting a go kart conversion as a MVP for a full scale conversion down the road.

We're currently getting stuck on our charge/discharge relay systems: we're using the Orion Jr. 2 BMS and AEV-250M contacts. The BMS is rated for a max of 175mA of current, but after preliminary testing we applied 8.75V to our relay to close the contact and had a current of 175mA.

I guess I'm wondering if we would be able to connect directly to the BMS or if we need to use an additional relay.

I've attached the wiring diagram for our BMS and the datasheet for our contacts, as well as a wiring diagram I've sketched.

All help is super appreciated!

 

[bwilson4web]

As a general rule of thumb, tapping inside a battery cell series is a poor technique because the cell balancing circuit will have to work much harder trying to get both banks equalized.

A better design would use a switching regulator to step part of the full pack voltage down to operate the relay. This will make cell balancing work easily and avoid asymmetric charge/discharge of the string. Suboptimal, cheaper, a current limiting resistor or cheap, linear regulator and resistor in series across the pack keeps the cell loads more consistent. But I am not happy with simple relay power contacts.

Given the potential for contact welding and arc aging, I would recommend a snubber circuit, a series RC circuit across the contacts. This will significantly reduce the current and voltage spikes on the relay contacts.

Bob Wilson

 

[bwilson4web]

Minor updates:

• buck regulator - get a small, single board, switching power supply as a single part
• snubber - a small RC board

This is the furnace pressure switch that failed Friday before Christmas. This original part has notoriously weak contacts that operate an inductive 'spark generator' load, the combustion fan, activation relay. To get a single furnace cycle, I used a jumper to fake the switch, 4-5 times each day over Christmas holiday.

The replacement switch assembly, $75, came in after Christmas and the snubber(s) the next day. The jumper was cut in the middle and soldered where the former screw-down terminal was located. Taped inside the static bag, it rests safely in the furnace.

Also, parts can be ordered from eBay for a reasonable price. Show the parts by closest to get them as quickly and cheaply as possible.

GOOD LUCK!

Bob Wilson

ps. For extra credit, describe an alternate snubber made with two Zener diodes and a resistor.

pps. Try to get an apprentice job with a small electrical business. It may take a year and won't pay well but the real value is learning practical electrical practices. With an electrician license, you will have guaranteed, alternate employment.

 

[Webie1]

Minor updates:

• buck regulator - get a small, single board, switching power supply as a single part
• snubber - a small RC board

View attachment 19656
This is the furnace pressure switch that failed Friday before Christmas. This original part has notoriously weak contacts that operate an inductive 'spark generator' load, the combustion fan, activation relay. To get a single furnace cycle, I used a jumper to fake the switch, 4-5 times each day over Christmas holiday.

The replacement switch assembly, $75, came in after Christmas and the snubber(s) the next day. The jumper was cut in the middle and soldered where the former screw-down terminal was located. Taped inside the static bag, it rests safely in the furnace.

Also, parts can be ordered from eBay for a reasonable price. Show the parts by closest to get them as quickly and cheaply as possible.

GOOD LUCK!

Bob Wilson

ps. For extra credit, describe an alternate snubber made with two Zener diodes and a resistor.

pps. Try to get an apprentice job with a small electrical business. It may take a year and won't pay well but the real value is learning practical electrical practices. With an electrician license, you will have guaranteed, alternate employment.

Hi Bob, thanks for all your help!

In terms of the electrician apprenticeship: do you think there are companies out there willing to do a 4 month apprenticeship (as that's all the time of between years I have)?

 

[bwilson4web]

Hi Bob, thanks for all your help!

In terms of the electrician apprenticeship: do you think there are companies out there willing to do a 4 month apprenticeship (as that's all the time of between years I have)?

One of the hardest engineering tasks I learned was to negotiate. I was hoping to go to the engineering lab and lock the door for a week.

My recommendation is to ask and be creative. Ask everyone.

Bob Wilson