Ben Nelson's Electro-Metro Build thread

[TheSGC]

Originally Posted by bennelson

Yep, I've got the BC-20.
I have a manual for it to....um..here...somewhere.

I did try using a Potentiometer in place of the resistor to make an "adjustable" for it. But that didn't work at all!

Please forward me any info you can on making your own resistor setup for it.

For anyone without the manual, Mr Sharkey has a copy on his web page.
http://www.mrsharkey.com/SCT/bc20.pdf

The BC-20 needs 1% resistors to function properly, and a normal Potentiometer is 5-10% tolerance, really really crappy.

I used a 1% 62K Ohm resistor in series with a 1% 20K Ohm Trimpot. This allows me to make small adjustments if needed. That, and I couldn't find a 76.whatever k ohm resistor to do the job, so I raided the schools supply room and found a way to make do and its been working fine for almost a year.

[bennelson]

I am trying to get ready for winter.

Temperatures have been dropping the last two weeks, and I can already feel that my batteries don't like it.

Today, at the EV Build Day, I built an under-battery warmer.

This consists of electric heat tape - which is used for keeping pipes from freezing, or snow turning to ice on the edge of your roof - stuck into some carved-down foam insulation.

I measured my back seat battery box, and cut a piece of 1" thick foam to 35.5" inches long and 15" wide.

Then I used a router to cut a groove 1/2" deep, back and forth, in the foam to make a serpentine path for the heat tape, and pushed that in.

This insulated heating mat will go under my rear batteries. The batteries will sit directly on the foam, and more foam insulation will go around the sides of the batteries.

When I wired up the "gas plug" in the car, I wired the other end, inside the spare tire well, with a standard electric outlet box. That way, one cable going to the gas cap charging plug can run the main charger, 12V charger, battery heaters, or anything else AC I need to run in the car.

Now the next step is to take out all the batteries to put the heating mat in, and then the batteries back on top of it!

[Christopher Jordan]

Some of my neighbours are pretty angry about my charging. Another neighbour wanted to put an electric blanket over his Harley motorcycle and the #$$^ really hit the fan. He gave up and moved. So far they can be angry at me for charging -but if I dare to add a heater they might stop letting me charge at all! You are more than welcome to experiment for me!! Good looking platform.

[Christ]

Ben, that looks pretty good!

Is the heater wire glued in to the foam?

[bennelson]

No, the heater isn't glued into the foam.

I cut the foam freehand with the router, and the non-straight lines make the heat tape stick into the slot very well. It certainly isn't going to fall out, but it does have just a little wiggle room, so when batteries are set on top of it, they aren't going to gouge the heat tape or anything.

[bones007]

Originally Posted by bennelson

I am trying to get ready for winter.

Temperatures have been dropping the last two weeks, and I can already feel that my batteries don't like it.

I don't have an EV but I am in the planning stages. I was also planning on having a battery warming system. I found this heating wire that is available at stores like Home Depot for not too much money:



I worry though that the system you are making may have hot spots directly above the wire that could damage the plastic covering of the batteries. I would suggest - and this is what I was planning too - to put a thin piece of sheet metal like this:

below the batteries to spread out the heat and avoid hot spots.


The wire can be fixed to the underside of the sheet metal using thermal putty like this from McMaster Carr (part number 3568K1)

it costs 30 bucks for a gallon. This is the cheapest stuff I found.


I would also suggest to put a thermostat inline with the heating wire. Thermostats like this one use a bi-metal contact that automatically switches off at a given temperature and back on at a given temperature. You simply put it in series with the wire - it can take the current of the heating element without a problem.



The device I have chosen is the 3455RC-100-222. It closes the circuit below 55 degF and opens the circuit at 85 degF:



Just fix it with the thermal putty to the sheet metal and it will automatically keep the plate below the batteries between the temperatures set by the particular thermostat chosen.

I hope this helps.

[MetroMPG]

Ben: glad to see you're addressing battery heat this winter. I thought of the electro-Metro last week when temps here dropped below normal, and I could really feel the effects in the little bit of driving I did in the uninsulated ForkenSwift.

No plans to address this issue with the ForkenSwift though - it probably won't be driven in the winter anyway, partly to preserve the car's body from more winter salt corrosion.

Originally Posted by Christopher Jordan

Some of my neighbours are pretty angry about my charging.

Why's that? Do you use a communal plug for power?

[bennelson]

Bones007 -

Thanks for the thoughts.

The heat tape that I am using has a built-in thermostat. You can see where there is a thick spot where the black tape becomes an orange cord. The thicker spot has the built-in thermostat in it.

I did talk about a heat-spreader plate with the guys. The thing is that this heat tape just does NOT get hot enough to actually make any hot spots. We tried some energy calculations, and found that just the heat tape by itself, in a perfect energy transfer, would take an entire week to raise the battery temperature 20 degrees.

No, this is only going to be something to help a little bit. I have another section of heat tape I am going to wrap around the sides of the batteries. Still, that's only 180 watts of electricity total!

Insulation is mandatory for this to work at all!

The talk of a heat spreader was for if I used the waterbed mattress heater I had. That would have been as much to protect the heater as to spread the heat. I went to a potluck farm party in a pole barn a couple weeks ago, and brought the waterbed heater to keep my casserole warm. Somebody else set a crockpot on the heater, and the pointly little feet wrecked the heater!

[bennelson]

The one thing limiting my upgrade to a higher than 72V system has been the charger. Specifically a little tiny resistor to change the output voltage of the charger.

At the last EV Build Day, I picked up a couple resistors, which rigged in series to each other, should get me the right resistance for the charger.
(Since then a friend of mine has also put in an order to a large electronics dealer, and I got in on his order for a set of resistors for the charger.)

This morning, I was able to upgrade the resistor, and I added three more batteries to the back of the car.

Of course, this takes up my trunk space, and I did love how "Normal" the car looked with just the rear battery box.



Now at 108V, my 0-100V analog voltmeter is pretty much useless.



I took the car out to run an errand, and test its performance.
I went up the BIG hill in my area, and the car seemed to zip right up it. Overall speed performance didn't seem like it was that much greater.

Coming back home, I was surprised that I couldn't get the car over 55 mph. It took me a while to figure out that it was because I was only in third gear! I needed to upshift to increase amps and speed. After that, I got the car just past 60, but by that time my pack was really getting run down and I had to get off the freeway.



A while back, I upgraded the rear springs of the car to some off the front of a Ford Ranger. These springs were really designed for holding 144V of batteries, which I HAVEN'T been running since then, so the back of the car has been riding high.

With three more batteries in back, the height of the back of the car seems to level out.



I am also trying to figure out the best way to keep my batteries warm this winter. Since I only have one traction battery under the hood right now, I might move it to the back of the car, just so all the batteries stay the same temperature. This would also drop the back of the car just enough to level it out.

The car is now charging in my driveway, but I am sure I will have to top off a few of the batteries with an individual charger to get them all even.

[Nevyn]

Put covers over the headlight buckets, and a small Kammback, and I bet your top speed and range will go up, and consumption will go down.