Electric car conversion: Project ForkenSwift

[MetroMPG]

MetroMPG The voltage sags pretty low under even light-modest loads. I've read it's best to try to keep the batts above 5.75v (individually) under load, and definitely go no lower than 5.5v. I can't accelerate at "normal" traffic rates and keep the voltage above 5.75, even on a fresh charge.

Crud! I keep mixing this up. So, correction:

5.25v is the conservative lower limit of sag under load for a flooded golf cart type batt, not 5.5v.

(Below 5.25v, you have no guarantee that an individual cell isn't approaching zero, and about to reverse polarity - pretty much wrecking the battery).

So trying to keep sag above 5.75v, while good for range and battery-friendly, isn't strictly necessary.

Which means that, when needed, I can accelerate more rapidly than I have been and not fear for the lives of the old floodies.

Also, using 5.25 as the lower limit effectively extends the car's range. Time for another range test!

[MetroMPG]

Another range test -

OK, just rolled in with 30 km on the clock (about 18.5 miles). Batts sitting at about 6.15v at the end after a 10 minute rest (compare to the previous 22 km run).

For context: coasted up to most stops, didn't exceed 50 km/h. Average speed was probably more like 35 km/h. Accelerated like a normal person (OK, a normal granny) and drove faster for the first 15 km.

But the last 5-8 km were pretty useless. On the final leg, had to leave it in 1st gear on 2 mild/moderate inclines to keep the volts from sagging below 5.25 - that translates to about 25 km/h)

Where did I go? I took some more of the deadest floodies in our collection to the recycler. Seems appropriate to do that using the vehicle that kills them.

And yikes - lead is getting pretty spendy: they gave me $5.60 per battery. Last time I was there I only got $3!

[MetroMPG]

Ben:

Nice job! You should make battery recycling into a business!

Well, I thought about it, but apparently copper recycling is more profitable.

I've read several stories lately about thieves stealing copper. In Halifax harbour, someone cut up an 11 km long copper cable from a dock crane that will cost $100,000 to replace. They were only able to actually make off with about half of it though. Crazy.

Yes, I've seen stuff like that online, that's it's big and all.

Last year when I worked at the shop the new guy would always talk about how people would steal the rain gutters and things for aluminum scrap. Crazy times.

[MetroMPG]

Moved the controller to a more "professional" looking installation.



Before: since April it's been strapped onto the transaxle, sandwiched between a dirty rag and a hunk of styrofoam (great heat dissipating properties, eh?)



Scavenged this aluminum heat sink from a dead 12v cooler. This is one half of the Peltier unit. It's about 8 inches long.





The Cursit's new home, chosen because there's a bit of space around it to potentially accomodate controllers of different sizes, should we decide to upgrade to a juicier unit (Alltrax?), or try out the forklift's EV-1 unit.

Unfortunately, when reconnecting the wires from the pot box to the controller, I shorted one. (Getting to be a bad habit!) Zorched the potentiometer. Fortunately, a replacement is just a couple of bucks at Radio Shack. Man, I'll tell you at that moment I was *very* glad I didn't spring for the $29 Curtis potentiometer! So I have an extra little project for tomorrow.

We're going to try to mount the rest of the hardware (contactors, fuse, shunt) on some kind of platform above the transaxle.

And that bungee cord connected to the top battery rack? It's holding up the forward end of the electrical conduit I put under the car on the weekend. Now that we know where the controller is going to be, it can be cut off at the proper length to run the cables where they need to go.

[MetroMPG]

Ben;

When's the date with the registration peeps?

It would be nice to have it on the road (legally) by the end of the month, but hey, would you look at that, it's nearly the middle of the month already!

You're only about a year behind schedule then! Good job, governor.

[MetroMPG]

To the assembled brain trust following this thread: can you help me come up with a ForkenSwiftish (ie. free or inexpensive) way to make a mechanical disconnect? We should have one in case of controller failure. Something that's activated perhaps by pulling a lever in the cabin. (I saved the hood release cable from the red donor car, or could use bike cable...)

A big red panic button would be good too, but it'd probably cost a bunch to get one...

[MetroMPG]

(duplicate post)

[MetroMPG]

I just read this yesterday, but can't comment on it:

Quote:
DC and AC contacting stuff is radically different and shouldn’t be inter-changed!

But then again, wouldn't a knife switch work on either AC or DC? It's just a simple switch. It would seem to me it's all about the current rating, and that's where you need to be careful. You probably can't apply AC ratings to a DC circuit.

[MetroMPG]

skewbe skools:

Apparently mr sharkey indicates greater arcing potential in DC (though AC is even better at arcing?!?)
http://www.mrsharkey.com/busbarn/electrics/chapt9.htm

But you are at 48 volts, and this breaker regularly sees 170 volts. And you wanted cheap

BigMouse adds:

Hmm, I remember from A&P school that DC switches have to have a higher rating than an AC switch because of the arc caused by turning it on or off. AC is able to sustain an arc, but a DC arc does more damage. This is why TIG welders have an high frequency AC 'starter' circuit, then once an arc is established, it switches over to the high-current DC.

I'm looking forward to seeing how you made your terminal ends. I'm getting to the point where I will need some, and I'm planning on using your method.

[MetroMPG]

Turns out there's a discussion about this on the EVDL this week. The issue is DC arcing, and one of the old hands says:

Quote:
A AC breaker at the same voltage of the DC source, does not have the larger
contact pads and spacing as a DC breaker. The spacing is contacts spacing
is wider in a DC breaker, so when a DC breaker is activated, there will be
less arc over.
He recommends going 3x over the AC rating for DC use:

Quote:
A circuit
breaker design for 3 hp load on AC is only good for 1 hp on DC. So it about
a 3 to 1 factor.
http://www.nabble.com/Clearing-the-a...html#a12646307

Mouse: I'll post a description of the lug making process soon, and come back and add pics later. I haven't made any new ends since last weekend. This weekend will probably be spent figuring out how to mount contactors etc.

I did sneak out and replace my fried potentiometer today though.