(ET) Inverter/Chargers for electric tractors

["Monty McGraw" <mmcgraw74 hotmail com>]

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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