Converting a miniature excavator to battery power

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HughF

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Jan 1, 2018
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I have a miniature excavator (mini digger, towable back-hoe depending on where you are from) that is powered by a Honda 270cc petrol engine, which has a maximum output power of 5.2Kw at 3600rpm.

I would like to look into converting this to battery electric power. Looking at the power curves, I think a 3kW GoldenMotor BLDC would be suitable - the machine is not underpowered with the current petrol engine and I never run it at maximum throttle, the controls are too fast for that.

I'm trying to think how to minimise motor runtime so that when your hands are off the controls, the motor stops. The hydraulics are open center, when the spools are all sat in the resting position the pump just circulates oil through the valve body. Perhaps something as simple as a foot switch throttle that runs/stops the motor when you press on it?

What would you guys do for battery options? I'd rather not import a 72v 18650 pack from aliexpress, mainly because I don't think they represent great value and the import duty risk is quite high. I could go with leaf modules? I don't need a high C-rate, and I don't need low weight...
 

jdeadman

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Mar 28, 2017
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Have a look for Forklift motors and controllers. they already have enough power to move /use hydraulic. The bigger the Voltage controller the better as you can drop the current down and then get a Large battery out of a car.

As for motor Off does the valving allow for off power holds? ie. hen the motor is off will it hold the arm where you left it? most have some blow by that will just let the arm fall slowly when the engine is off. If that's the cae you will want the motor running the entire time you are at the controls. but even at 3kW motor it would take quite a while to burn up a 30Kwh Leaf pack
 

HughF

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jdeadman said:
Have a look for Forklift motors and controllers. they already have enough power to move /use hydraulic. The bigger the Voltage controller the better as you can drop the current down and then get a Large battery out of a car.

As for motor Off does the valving allow for off power holds? ie. hen the motor is off will it hold the arm where you left it? most have some blow by that will just let the arm fall slowly when the engine is off. If that's the cae you will want the motor running the entire time you are at the controls. but even at 3kW motor it would take quite a while to burn up a 30Kwh Leaf pack
Forklift motors are a terrible idea, they're normally just aseries wound brush motor, like a car starter motor.

The hydraulics are open center, the pump will circulate fluid round the valve body without resistance when all hands are off - hence you can shut off the motor/engine and the boom rams will lock. The spools are spring closed, and yes they weep a tiny amount, which is not of concern. I rest the boom on the gound when leaving it for any length of time and I have transit locks for towing it.
 

Headrc

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Jan 27, 2018
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This is an interesting project, and whatever direction you choose I would like to know about your progress. I have a mini skid steer and find it to be one of the most used tools around our farm. On my to-do list is to build a remote controlled mini skid steer but my approach would be different. In my arsenal I have a diesel powered Greensking mower that is all hydraulic. I purchased it specifically to pull the motor and all the hydraulics off of it to build a RC controlled mini skid steer.I think Iwould keep the diesel motor to drive the hydraulics and use RC controlledactuators to control the little beast. The purpose for the device would be for all those dangerous places on our land that I would like to clean up without doing it by hand. But of course this project so far has been on the wish list and has not been started yet.

If you do build a battery pack and decide to do it with all new batteries, you might consider the Boston Power line of batteries. They are very good batteries and can offer a good cost benefit for what you get. And yes, I do have a good quantity of them and sell them ...but you can source them from others as well. I make the recommendation because I have a good bit of experience on different projects with them and believe that they are an under rated choice. If interested you can PM me and I can put a package together for you....or just look for a source like Queen Battery on Aliexpress. I can supply specs if you want it on the batteries.
 

HughF

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Jan 1, 2018
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To be honest, I'm leaning towards used leaf cells - mainly due to the availability here in the UK.
 

Jon

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Aug 20, 2017
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The power draw of the hydraulic motor circulating oil when the control spools are open will be minimal.
Id just put a easy to get to switch to toggle it on/off.
Is it twin joystick control or multiple levers? If its twin joystick Id do a thumb switch on one of the levers, if its multiple levers then maybe a foot switch.
What about a seat switch?, how often/long are you in it without operating it?
 

HughF

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Jan 1, 2018
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Jon said:
The power draw of the hydraulic motor circulating oil when the control spoils are open will be minimal.
Id just put a easy to get to switch to toggle it on/off.
Is it twin joystick control or multiple levers? If its twin joystick Id do a thumb switch on one of the levers, if its multiple levers then maybe a foot switch.
What about a seat switch?, how often/long are you in it without operating it?
It's a 4 stick machine, and I'm regularly on and off the seat because I'm often working on my own (the powered wheelbarrow I often use with the digger is too madly uncontrollable for my wife to use) so a seat switch makes perfect sense. I had not thought of that. Genius...
 

Korishan

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Here's another option to minimize motor usage:

Use the pressure of the hydraulic to trigger motor so that when it detects a drop in the line, the motor turns on powering the hydraulics back up. As long as there is pressure changes, the motor will continue to run. But when you stop also have a timer on it so that it'll stay running for like 15 seconds or so.
I've seen some electric reach lifts that worked in this manner, tho it was going off the electric trigger instead of a pressure sensor. Once you stopped using it, the motor would continue run for about 5 seconds before spinning down.
 

Jon

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Korishan said:
Here's another option to minimize motor usage:

Use the pressure of the hydraulic to trigger motor so that when it detects a drop in the line, the motor turns on powering the hydraulics back up. As long as there is pressure changes, the motor will continue to run. But when you stop also have a timer on it so that it'll stay running for like 15 seconds or so.
I've seen some electric reach lifts that worked in this manner, tho it was going off the electric trigger instead of a pressure sensor. Once you stopped using it, the motor would continue run for about 5 seconds before spinning down.

You need closed centre rather than open centre hydraulics to run that style of system.
 

HughF

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Right.... Orion Jr BMS, eltek flatpack charger, leaf cells... All I need now is to decide on a motor/controller combination. Does anyone have experience with the golden motor 3kW (5kW peak) motor and controller?
 

Korishan

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Jon said:
You need closed centre rather than open centre hydraulics to run that style of system.

Had to look up the differences :p

Couldn't you just put a sensor on each outflow port? Sure it would require more sensors, but would it work?
 

HughF

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Korishan said:
Jon said:
You need closed centre rather than open centre hydraulics to run that style of system.

Had to look up the differences :p

Couldn't you just put a sensor on each outflow port? Sure it would require more sensors, but would it work?
Yes, or put microswitches on the levers so when you go to move a lever, the pump starts.

I've just realised, I need a motor controller that has a cruise control mode - it needs to maintain a governed speed independent of motor load. Can't have the motor slowing down when the hydraulic pump loads up.

GoldenMotor controller definitely has this, I'm also looking at the Shinegle 5Kw motor kit (might be cheaper), not sure if this controller has a constant speed capability.

For some reason I can't attach the power curve .jpg for the 5Kw motor :(

View attachment 6
 

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  • 5kw AC motor and controller specification .pdf
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Jon

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Korishan said:
Jon said:
You need closed centre rather than open centre hydraulics to run that style of system.

Had to look up the differences :p

Couldn't you just put a sensor on each outflow port? Sure it would require more sensors, but would it work?

Technically yes, if you were going to go to that sort of extent you could probably put strain gauges on the levers to sense control input. That would happen before the system pressures changed at all. Most machines dont have operators in the seat without them doing something for extended periods of time. The hydraulic system cycling fluid without any load will draw very little energy as a percentage of daily use.
 

HughF

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Jon, are you in the UK bychance?
 

HughF

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Shinegle controller manual attached, for reference. Has anyone used this motor/controller combo?

View attachment 7
 

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  • SG Controller 12X2.pdf
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Jon

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HughF said:
Jon, are you in the UK bychance?

Hi Hugh
No, a bit north of Brisbane, Queensland, Australia.
A cool project you have going :) I hope you share progress
 

HughF

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Jon said:
HughF said:
Jon, are you in the UK bychance?

Hi Hugh
No, a bit north of Brisbane, Queensland, Australia.
A cool project you have going :) I hope you share progress
I will keep the group informed of my progress... I'll probably convert my powered wheelbarrow to electric power too...


image_wswpel.jpg
 

completelycharged

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Interesting project...

The 3kW motor will more than likely out perform the 5kW petrol on torque. The motor will need to be geared down quite a bit. Find out the model and efficiency chart for the primary hydraulic pump and then match the rpm output from the motor.

Is the primary pump a single or multiple unit ? Does the flow divide up between boom and turn/motion or is it multiple output ?

"Yes, or put microswitches on the levers so when you go to move a lever, the pump starts." - this might have an issue with starting torque if the system has a load.

Does the pump have a centrifugal clutch between engine and pump ? This is the default and easiest way to unload or gradualy load the pump, I have done this approach on 3 hydrostatic machines I built (1 x 10hp diesle and 2 x 20ph v-twin petrol).

I am looking to build a hybrid electric/hydrostatic or all electric off road unit but the motors are the main issue (waterproofing on bearings for submergence) hence hydrostatic hybrid so the hydralic motors can sit underwater when traversing a river.

The wheelbarrow could be quite interesting, could use a geared stepper for the lift. Depends on how heavy or much weight you have to play with for the electrics.
https://www.omc-stepperonline.com/n...12-nm-1699-68oz-in-6-0a-110x116mm-4-fili.html
Stepper driver and separate CNC style controller (use stop limits and start/stop).
 

HughF

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Jan 1, 2018
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The gas motor runs at 3600 maximum, j usually run it around 2800-3000 for smoothness of operation. I think the 3kW golden motor has an ideal power curve for direct coupling to the pump.

The pump is a simple, single pump, no clutch. It is a walking digger (like a towable backhoe) so has a slewing ram but does not have traverse motors.

I'm just pricing up battery options at the moment. Aiming for 4 ish kWh at 48v, if I can
 
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