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Yes, my intention would be to replace only the motor and hydraulic pump. I'd select the new pump based on the ideal operating range (in rpm) of the new motor. I'd select a pump with the right displacement to give me the flow rate I want at that rpm. There is only a single pump, delivering flow to both the drive motors, lifting and tipping rams, as well as the auxiliary hydraulic circuit.
Your machine may be different, but in this video @~4:18 there are 2 pumps driven in tandem off the end of the engine. They are in the long black cylinder, center lower picture frame. The one on the right, with the larger oil feed hose, is the drive pump. The one on the left, with the smaller feed hose, is the cylinders and aux pump(usually). The size of the feed hoses and the lengths of the pump sections correspond to the oil flow rates of the 2 pumps. The longer drive pump has a higher flow rate and needs more power to do this. This is a typical set-up:
. Coincidentally, even in a modern mini ex (Kubota KX040 is what I have the most time in), I've never operated at full throttle. I only notice more speed over the ground when driving around, but no more digging power.
All right, we're getting close here. Now, envision your mini ex moving forward and back at travel speed as the boom, arm, and bucket are being operated. In reality, this would never happen as the machine operates in a semi-fixed position. But, this is how a skid steer operates.
 

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Yes, my intention would be to replace only the motor and hydraulic pump. I'd select the new pump based on the ideal operating range (in rpm) of the new motor. I'd select a pump with the right displacement to give me the flow rate I want at that rpm. There is only a single pump, delivering flow to both the drive motors, lifting and tipping rams, as well as the auxiliary hydraulic circuit.
That works, but wouldn't the original pump work, too? With the original pump, a gearbox would help to match the pump speed to the (higher) motor speed; with a new pump, you could choose it to work at the best speed for the motor.

Drive motors are a nightmare. I wouldn't dare try to swap them for direct electric motors. These use a pair of motors with an oil bath chain mechanism between the wheels. Not trying to re-engineer that :)
I assume that a conversion eliminating hydraulics from the wheel drive would keep that chain system, and replace only the hydraulic motors with electric motors. It still wouldn't be trivial, largely because a new control system would be needed.
 

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Are we coming to the conclusion that this particular motor (AC 9) is underpowered for my application?
Yes, I think so, but that depends on how much power you actually need on average.

It seems a bit dishonest by the seller and manufacturer. Why sell a motor with a 600 A controller if it will set itself on fire with less than 1/3 that amount of current through it?
The controller is spec'd to meet peak motor demand, and the motor can do that briefly. If they packaged the same motor with a 200 amp controller they would be accused of providing inadequate equipment for applications that briefly use the peak power.

The key is to understand that when a motor is listed as producing "up to 27 kW", there's a reason that it isn't listed as simply "27 kW".

The DC motors all seem capable of running at their rated current without issue (again, the ME1004 is rated at 200 amps, and will run 200 amps all day).
Not really. Many DC motors are sold with output specs that they can only meet momentarily. Given the information that I've seen from Motenergy, I would be wary of any of their specs, but for the ME1004 specifically they say:
Capable of 200 amps continuous, and 400 amps for 30 seconds.
... so 200 amps is the continuous rating, and they do claim higher.

Can we squeeze more current with active cooling???
Better cooling is certainly the way to enable continuous operation at a higher power level. Retrofitting cooling might be practical, but generally doesn't work well. The AC 9 is designed to be cooled by its fan; there are other motor models from HPEVS which are available with liquid cooling, but only in larger sizes of motors intended for higher voltage (than 48 V).
 

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Discussion Starter · #24 ·
I was able to dig into the machine a bit, and as mentioned above, it may well be a tandem pump (why JCB oriented things with the pump buried all the way forward toward that cab I'll never understand). I have a service manual, but I'm on the lookout for a parts book ($90 on ebay right now...haha I'll wait). I'm having a hard time figuring what the specs (displacement) are for the stock pump without any part number.

This brings up a new consideration of splitting the system into two motor/pump combinations, one for the drive wheels and one for the lifting circuit. This would allow smaller motors, which might work with my self-imposed voltage limitation.

I guess some of the benefits of the above mentioned AC-9 setup might be lost on my application. The motor control for AC motor is much more expensive than dc motor. I don't need regenerative braking, or any kinds of acceleration control. The pump basically just needs to run at a constant RPM. Can I use a DC motor without motor control at all??? Voltage being the determinant of speed? I could use less expensive motors in multiples. Could even drive each drive motor with a separate pump. Decent quality gear pumps are relatively inexpensive in the context of AC motors, controllers and batteries.
 

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In a second look at the frame from the JCB video, the gray part of the pump set-up, to the far right, might be a variable displacement pump driving the wheels. In this case, there would be 3 pumps in tandem. Maybe, the auxiliary attachment pump is one of the black pumps.
A large DC shunt( preferably a sepex) motor from a larger forklift run with minimal speed control (constant speed) might work in this application. A series motor may not have sufficient load to prevent a runaway condition. I'm just not sure what size the motor needs to be. It maybe in the end you'll have to do some experimentation with motor sizes. Do some research on other conversions or talk to forklift people for their opinions. The nice thing about the existing tandem pump set-up is that there would be just one splined coupling(or possible a flange) needed to attach the motor to the pumps. You probably should be prepared to over-volt(to 60-72V?) the motor the have sufficient power. You may have to limit the RPM( and voltage) for motor safety/durability and possibly to prevent pump cavitation.
 

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About four years ago I converted a 1983 Thomas skidsteer to electric drive.
The smokey old diesel engine (28.2 hp @ 2800 RPM) was replaced with a
Netgain WarP 9 72-156V 500amp motor 32 HP
Curtis 350 amp motor controller
Battery is 6-12V deep cycle
Onboard Quick charge battery charger
and a separate 72V solar charge controller with one 260 watt solar panel
The Netgain motor is connected to the 3 inline hydraulic pumps with a splined u-joint
I usually run about 30 min-small jobs around the property-enough for me
 

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The pump basically just needs to run at a constant RPM. Can I use a DC motor without motor control at all??? Voltage being the determinant of speed?
A motor's speed is not simply determined by voltage. If you supply constant voltage to a motor, it will run at the no-load speed determined by that voltage and back-EMF (which is turn depends on motor design), but will slow down as load is added. If the supplied constant voltage is high enough to keep the speed adequately high under high load, the speed without load may be excessive. Since the load when driving a hydraulic pump will vary greatly, my guess is that running without a controller wouldn't work well, but someone may have experience trying this.
 
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