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Converting a miniature excavator to battery power
#1
Tongue 
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...
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#2
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
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#3
(08-28-2019, 12:42 PM)jdeadman Wrote: 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 a series 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.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#4
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 I would keep the diesel motor to drive the hydraulics and use RC controlled actuators 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. 
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#5
To be honest, I'm leaning towards used leaf cells - mainly due to the availability here in the UK.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#6
That could be a solution of course.
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#7
The power draw of the hydraulic motor circulating oil when the control spools are open will be minimal.
I’d just put a easy to get to switch to toggle it on/off.
Is it twin joystick control or multiple levers? If it’s twin joystick I’d do a thumb switch on one of the levers, if it’s multiple levers then maybe a foot switch.
What about a seat switch?, how often/long are you in it without operating it?
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#8
(08-28-2019, 07:33 PM)Jon Wrote: The power draw of the hydraulic motor circulating oil when the control spoils are open will be minimal.
I’d just put a easy to get to switch to toggle it on/off.
Is it twin joystick control or multiple levers? If it’s twin joystick I’d do a thumb switch on one of the levers, if it’s 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...
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#9
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.
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#10
(08-28-2019, 10:18 PM)Korishan Wrote: 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.
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