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(ET) Inverter/Chargers for electric tractors



I agree with Dan on the inverter. After much searching, I picked the Trace DR1524 1500W AC inverter and 35Amp 24 volt battery charger. I really would have liked a 1548, but they don't make it.

I am still going to use 48volts (six T-875 Trojan 8V deep cycle batteries used in the newer 48V Club Car golf carts - and the same batteries I put in my 144V 1988 Pontiac Fiero GT conversion!).

I am going to use a reversing contactor to switch the batteries from series to two banks of 24V in parallel when I plug the AC charging cord into the Trace inverter. During tractor operation, I will allow one of the banks to power the inverter for 'small' loads while driving, such as really inexpensive AC powered halogen work lights, etc. When parked, I can throw a switch on the dash to bank switch the batteries to 24volts parallel to get maximum AC inverter power (but the tractor power will be totally off). The secondary benefit of the contactor will be for tractor power disconnect in the event of a problem.

This inverter is a modified square wave inverter rated for 1500W continous and up to 4500 watts for one minute or 3000 watts for two minutes overload! The efficiency is 94% max and the unit only weighs 35 pounds. The charger is a three stage charger with algorithms for deep cycle lead acid, Gel cells, Nicads and even Lead Calcium telephone batteries. It has switch positions to allow manual equalization charges for regular deep cycle lead acid batteries, say once a month. There are adjustments for battery Amp-hour capacity and battery charge rate in bulk mode. This inverter/charger is typically used in the solar energy business to convert the stored solar energy into AC power, while the charger is used to top off the batteries when AC is available.

The three modes of the charger are bulk, absorption and float. Bulk charge (at the adjustable bulk charge rate up to 35A) is constant current, until the battery pack reaches the bulk charge voltage (they have tables for two different settings for deep cycle lead acid batteries). At this point the charger automatically switches to absorption mode where the bulk voltage is maintained constant and the current begins to drop as the batteries increase their state of charge. Stage two charge is terminated either by the charge current dropping to battery bank capacity/40 OR within 12 hours. Stage three charging is maintain the battery pack at the float volts setting continuously.

I have a similar automatic three stage charger in my Fiero (Zivan) and it does a great job of keeping the batteries well charged with minimal water loss. I got the Trace cheaper than a 48V Zivan charger and separate 24volt inverter with the above specs. The inverter will be mounted under the front hood, above the batteries.

Because of the corrosive fumes during battery charging, I will be plastic welding polyethylene enclosed battery boxes for front and rear with blowers powered by AC when charging, exhausting the air through the holes in the bottom of the boxes and main tractor chassis. This has been done in full size EVs.

BTW, I am completely replacing the original wiring (some relays and components were 'borrowed', some of the wiring looks like it has been chewed on). I am using a 4QD 300A 48V solid state controller that has full regenerative braking capability and reverse operation without using contactors! I will be using a smaller 1QD 70A 48V controller to drop the 48volts to 36 for standard PTO use (I'm concerned about overvoltage for permanent magnet motors). I am using a surplus 48V to 12V DC-DC converter for the dash light and maybe the headlights if I decide to keep them 12V, and some 12V cooling fans for the controllers. Hopefully this will keep the battery packs more even, with the only 'tap' at 24V to the inverter, but the idle current on the inverter is only 30mA.

Right now I'm still working on the electrical design, I have the controllers and inverter and will be benchtesting some of my concepts by next week.

Monty McGraw
restoring an E20

From: Daystar Energy Services <daniel laser net>

A word of caution. Twenty or thirty year old inverter technology, in my opinion, will be ineffiecient and potentially very hard on devices that you run. Many newer, especially larger, inverters are also three stage, programmable, smart chargers. That would allow you to dump that bogus ET
bulk charger and timer. The problem that I had was finding one that
would take 36vdc. That's why I made a 24v tractor. Try Heart Interface
or Exceltech.

Dan


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