# Electric power for Hydraulic power pack



## madderscience (Jun 28, 2008)

I know that forklifts have hydraulic pump motors on them but I doubt any of them are rated for 16hp continuous. Maybe something really big.

In the DC car conversion realm, an 8" or 9" DC motor like an advanced DC or warp would have the continuous horsepower capacity to do what you need. 

However, give your situation you might go for more of the industrial equipment route. Find an appropriate VFD (variable frequency drive, look on ebay, plenty of them in the horsepower range you need) and a compatible (inverter rated) 3 phase industrial motor with the right ratings and use them. Many industrial VFDs can be hooked straight up to a DC power source (e.g. batteries) instead of AC, and they all can with some hacking.

You will need to do some math to properly size your batteries. 20HP * 746 watts is appoximately 15KW. Multiply that by the number of hours of run time you want between charges and multiply that by a factor of two (at least) to give safe margin and account for inefficiencies in the system. For example, if you expect a 20 minute run time between charges to go that 200 feet, you will want a battery pack of 15KW * 1/3 * 2 or a 10KWh pack. Assuming the nominal DC supply voltage of 300V to your VFD that works out to about a 33AH battery. This is well within the same scale of things as your typical roadgoing EV has (actually, smaller). 

If this system is used very infrequently then battery maintenance may be an issue. Some battery chemistries (e.g. flooded lead) need a certain amount of cycling for maximul life. Batteries intended for standby usage, like UPS batteries or AGMs would be best in the lead acid realm, and prismatic lithiums would probably do quite well also. In any case, a 10KwH battery pack is going to weigh well under 1000lbs with lead, and only a couple hundred pounds with lithium so space won't be a issue.

Good luck.


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## JRP3 (Mar 7, 2008)

Since the motors will run at a constant speed VFD's and AC motors sound like an expensive way to go. Why not just use shunt wound motors and contactors?


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## Mark Sharin (May 22, 2011)

Thank you for your quick replys. I would most likely stay with a DC traction motor for this project as I only need two maybe three speeds at the most and then doing any speed changes with the hydraulics. One to run the motor at maybe half power, one to run at full and one for a short burst at peak only in an emergency. As for run time it would be up to 2 or 3 hours at the most at any one time and the system would probably have less than 80 hours total run time all year.

If it is run by contacts for just the 3 speeds is that done by drawing from only a few of the batteries then adding banks as additional contacts are made or can you draw from all banks for all settings. (That is the one area where the VFD seems to be a big advantage.) For batteries we would most likely be using 12 volt 8D batteries like those that are used on heavy equipment. Although the 6 volt golf cart batteries have not been ruled out. 

What voltage would you recommend using for the system. Would 96 be enough or would I be better looking for something higher? I do understand the the higher the voltage the lower the amps that would be needed for the same total output.

As far as cable runs are concerned they could be made very short and would be made out of welding cable.

We will most likely be keeping 2 systems (at the 15-20 constant to 40 peak) because I didn't think it would be practical to have one motor to do 30-40 and up to 80 peak. Plus we have the pumps already and would just have to mount the new electric motors to them.

We originally thought of going with the electric system based on our usage with the Citicar which has been in the family since the '70's. It seemed to be a similar load with just a few speeds but we would need more then the 3.5 HP its motor produced at 48 volts. If I get the time to build an EV I would definetly go the AC with a VFD route.


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## JRP3 (Mar 7, 2008)

When I suggested contactors I was considering a single motor speed setup. Yes you could use multiple contactors to engage more batteries to increase speed but you'd be better off using a controller instead if you want to modulate power. An Alltrax 72 volt 450 amp controller might do it, you'd have to check the continuous power rating. 
http://www.evdrives.com/alltrax_axe7245.html 
Higher than that you're looking at a Curtis or Soliton Jr.


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