Project: The Electric Booger (budget EV conversion - '92 Mazda MX-3)

[mechman600]

Originally Posted by MetroMPG

Also, FYI, I operated under the assumption that 5000 RPM was the redline, but I rarely if ever got that high.

Ha ha...I got it that high in neutral in my garage yesterday!
Is the 5000 RPM figure something that you got from somewhere or was that a number you came up with?

I love the sound of this motor. It has a Jetsons vibe. Sometimes I drop a gear to enjoy it. (Just like I do when I drive my Ferarri through tunnels & underpasses.)

LOL. You are right - this motor sounds really cool when the revs are up. Jetsons with a touch of cooling fan.

[MetroMPG]

If I recall, 5k came from an email discussion with Jim Husted - expert motor rebuilder of EVDL fame. And from reading about someone who detonated their similar sized series motor at around 6k in a Civic wagon conversion.

[mechman600]

Today I wired my ex-low oil pressure light to turn on when my brake vacuum pump turns on. The vacuum switch was already grounding the vacuum pump relay coil, so why not use it to also ground the unused idiot light? This will give me a nice bright indication that the pump is on when I am driving at such speeds that the road noise is to noisy to hear it.

However, much to my delight, I killed two birds with one stone. With the vacuum switch now carrying the current of the added light bulb to ground, the relay chatter that occurs when the pump turns off is for some reason completely gone now. I thought the chatter was some sort of vacuum pulsation/incorrect placement of the vacuum line to the switch issue, but it turns out that it was some sort of electrical inductive issue, probably caused by the coil in the relay.

Weird.

[russatt]

Hi

I have just finished reading this whole thread. It has been very informative, thank you. I am a first time EV'er. Still in the planning phase. I have also been considering 12 x 12v 100a Lead Crystal Batteries. Sorry to go off where this thread is now, but I have a question about your array of volt meters. When the contactor is closed for your series of batteries, do you have some diodes inline with the voltmeters for each independant battery. Shouldn't they cause a dead short in series and parallel at the same time.

[mechman600]

Welcome, russatt.

No diodes required. Remember that a voltmeter has an incredibly high internal resistance. Otherwise even checking the voltage of a battery between the posts would cause a massive short circuit.

Chargers are another issue. Only isolated chargers can be used in the way I am or else there will be a massive short circuit through the AC side.

[russatt]

Ok thanks.
I was also considering a high power 12v charger, and then charging the batteries in parallel, so that they can equalize, but I am not sure if it will be safe with the batteries in series as well, contactor open, and what diodes and components would also be required.

This charger is 12v 320 amps max. Adjustable.
Would it work, or is this a bad idea.

[mechman600]

Originally Posted by russatt

I was also considering a high power 12v charger, and then charging the batteries in parallel, so that they can equalize, but I am not sure if it will be safe with the batteries in series as well, contactor open, and what diodes and components would also be required.

This charger is 12v 320 amps max. Adjustable.
Would it work, or is this a bad idea.

In theory it will work. However, you need contactors or disconnects between each battery so nothing is connected in series while charging in parallel and a way to disconnect all charging wires so nothing is connected in parallel while driving the car with the batteries in series. Diodes will not work.

For a 72V system, this would require a minimum of five contactors/disconnects to open all series connections and 12 separate switches for charging circuitry. Everything would have to be well protected (fuses) in case even one component failed, causing smoke to be let out of something.

[russatt]

Ok Thanks for your help.
It definately leans more towards the bad idea side.

[mechman600]

Today I completed my new fangled battery monitoring system. No pictures yet, but maybe I will do a video tomorrow. I am very happy with the end results - it works pretty slick.

I went for another rip around the block today. This time I got it up to a higher speed, and wow...this motor has a LOT more torque than the old motor. It also seems to maintain the torque up to the same RPM as the old motor, which is weird. I thought it would be torquier but slower. A welcome surprise.

I am very interested to see how the car's efficiency will change. I suspect it should get better, since I am now controlling a proper motor for my controller. Once I start commuting I will know for sure.

[MetroMPG]

Once you start commutating?