Hydraulics

I've decided to tackle converting the hydraulics to electric drive first. First thing to work out is how big a unit is required. That means taking a few measurements:

Flow

First thing to work out is the bore and stroke of the main ram. With the boom fully extended I measured this:

And came up with a stroke of 480mm and a rod diameter of 60mm. I'm not sure how the rod diameter relates to the internal cylinder diameter, but I'm going to guess it's maybe 65mm. That means the volume used to extend the cylinder fully is about 1.6 litres.It does this in about 9 seconds, so that's a flow rate of 10.7 litres per minute.

Pressure

To work out how much power is needed to lift the boom, I need to know the pressure required. If I knew the mass of the boom I could probably work it out theoretically, but I decided to go the direct route. This is the supply into the base of the ram:

The brass bit between the hose and the entry to the ram looks to be a flow restrictor - I assume it's there to limit the speed of the boom so it doesn't drop like a stone if the hydraulic hose bursts.

A quick trip to the hydraulic shop and:

With the gauge in place I was able to determine that the unladen operating pressure of the ram was 35bar, and with my 86kg on the operator's platform it goes up to 70bar, or 1,000psi, which is pretty low pressure for hydraulics.

Power

So knowing this info (flow and pressure) it seems there's a neato formula for determining the input power required. It's simply 

(flow x pressure) / (600 x eff)

The eff. term is the efficiency of the system and the answer is in kW. That gives me:

(10.7 x 70) / (600 x 0.7) = 1.8kW or 2.4hp

My term for system efficiency is totally made up. I assume hydraulic pumps are about 85% efficient and electric motors maybe 80%, that gives 70% total efficiency.

A bit of snuffling around Ebay turned up a 24v 2.2kW hydraulic power pack from a stock picker (a kind of forklift). I'm hoping it'll do the job - if the boom lift is a bit slower that's not a huge issue, as it's probably quicker than it needs to be at the moment.