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Old 03-26-12, 08:32 PM   #11
dh1
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Quote:
Originally Posted by Daox View Post
Here is my break down:

~$1235 total

(3) Batteries = $295
Pulleys = $35
Battery rack material = $35
Misc. hardware = $15
Rest = Free (freecycle.org and buddies at the local EV club)
Snowblower attachment (9/9/09) - $100
Two new batteries = $265 (6/4/10) (blew one up & upgraded to 48V)
Chargers = $195 (8/14/10)
Mars ME0708 Motor = $295 (10/22/10)

More info:
Tim Fulton's Simplicity Broadmoor 728


I could have saved a lot of money by buying more used parts (brand new batteries were almost 1/2 the total cost of the project). However, I didn't have a lawn mower at the time and needed something working to cut the grass! Now that its all together I wouldn't ever want anything else. I really do love it.
You got your motor for a good price, my slightly used Etek cost me $400.
Batteries I figure are going to cost $400. to $700. +???
I'll need a 48volt contactor and a 1 or 2 meters.
Everything else I have or can make.
So I figure this conversion will cost $1000. to $1500. ???

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Old 03-27-12, 06:58 AM   #12
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Yeah, I found a great deal on my motor on ebay. Just got lucky. It was used, but it was just bench spun. The brushes weren't even worn in yet.

I just run my contactor off one of my 12V batteries. It only pulls 1A and I have individual chargers for each battery so they all get topped off once plugged in. If you're interested, I have a couple extra laying around. I got a small bin of them from the local EV club.
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Last edited by Daox; 03-27-12 at 07:08 AM..
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Old 03-27-12, 07:34 AM   #13
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Thanks Daox.
I have some 24volt contactors and was thinking of using 2 of them.
They are 4 terminal, 2 small terminals for the coil, and 2 large terminals for the load.
I was going to wire the 2 coils in series so I go across 48volts, the whole pack.
Wire the load terminals in parallel, so that only 1/2 the motor current goes through each contactor.
Think it will work?
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Old 03-27-12, 09:30 AM   #14
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That will work, but you need to be careful about how you wire up your power switch(s). You'll need individual circuits to power each of the contactor's coils otherwise you will run into problems.

So, you'll want something like this:




Also, you won't be able to switch on both contactors at the exact same time. So, for however long that delay is, that first contactor is going to be transferring all the amps, and these are startup amps so it'll be pulling more than normal operation.

It would be much simpler to just use one contactor. If you have individual chargers you don't have to worry about the batteries being unbalanced.
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Old 03-27-12, 11:17 AM   #15
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That's the idea but just 1 switch. I don't know how to draw pic on the computer.
Batt+ 48volts to 1 coil A small terminal.
other small terminal coil A to 1 small terminal coil B
other small terminal coil B to Batt-
If both coils the same voltage drop across them should be the same, 24volts.
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Old 03-27-12, 11:26 AM   #16
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Yeah, that sounds like it should work fine.
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Old 04-05-12, 09:21 AM   #17
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Quote:
Originally Posted by dh1 View Post
That's the idea but just 1 switch. I don't know how to draw pic on the computer.
Batt+ 48volts to 1 coil A small terminal.
other small terminal coil A to 1 small terminal coil B
other small terminal coil B to Batt-
If both coils the same voltage drop across them should be the same, 24volts.
It's much easier/straightforward to drop the voltage with a resistor rather than using a second contactor coil if you want to keep the load spread across all the batteries: Measure the current through the contactor coil at the rated voltage (i.e. 24V in this case), say it's 0.150A. Divide the voltage by the current to get the coil resistance (24V/.15A = 160 ohm). So add a 160 ohm resistor (anything between 140 and 180 ohm would be fine) in series with the coil (i.e. - bat to one side of coil, other side of coil to one end of the resistor, the other end of the resistor to your on/off toggle switch, the other side of your switch to 48V) and you have a balanced load across the whole string, but the coil running at half the string voltage. Note that the resistor needs the appropriate power rating: 0.15A*24V=3.6W, so use a 5 watt resistor, or three 50-ish ohm two watt resistors in series, or three 480-ish ohm two watt resistors in parallel.

If you already have the second contactor and don't want to make a trip to the resistor store, using the second coil to drop the voltage is also fine, but there is no need to run the power through it's contacts... just wire up the two coils in series and run the motor power through one contactor and you're done (assuming it's rated for the motor current).

Dang it... an electric mower wasn't even on my list of things to do until I read this thread!

-Pete
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Old 04-19-12, 01:29 PM   #18
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Any updates on this project?
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Old 04-19-12, 08:44 PM   #19
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Any updates on this project?
Nothing really to report, I have a piece of 1/4" steel plate for the motor mount, just need to cut to fit and drill some holes in it. Also I have the steel for Battery racks.
The hold up right now is batteries, it's a toss up between a cheapy set from Wallmart or a good set of Trojans, 1275s. Oh and the $$$ for them.
Lately I've being working on my gas ones, I have 5, I want to sell this yr. Going to just keep the really good ones that I need for myself. No Electric tractors will be sold, I like that stuff.

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