12 to 24 vdc onboard battery charging - high current load

[jas165]

I am developing an electromechanical system for a class 8 tractor/trailer rig that requires a large 24 vdc motor to provide hydraulic power to trailer equipment. There is also ancillary equipment such as transducers, valves, and a controller that will consume a small amount of power relative to the motor.

The tractor has available 12 vdc. Due to the high inertia of the pump/motor group, the proposed motor current draw is 53 Amps at no load. During normal operation the motor will consume between 92 and 125 Amps, depending on external load. The peak load for extraordinary conditions is 166 Amps. Would like to continuously run the motor at vehicle speeds<30 mph for the purpose of quick control response. For speeds>30 mph the motor would be off.

As usual, weight, space, and cost are constraints for which to design around. I am currently looking at a power system consisting of qty (2) independent 24 vdc battery banks. Each battery bank would have an independent booster/charger such as the digital mobile charger from onboard solutions.

Desire to continuously charge both systems when vehicle engine is on. Propose to power the motor from qty (1) of the battery banks while the other is charging. When the loaded power bank drops to a pre-set voltage level, I desire to seamlessly switch to the other bank. In this way I hope supply power to the motor by alternating the battery banks.

It might also be desirable to always have the controller and other devices on the opposite bank that is powering the motor.

Anyone have comments, opinions, or better ideas?

 

[itsmoked]

Comments...

You should re-think this. Look around. Do you see this system on other trucks/mobile systems? If you don't it's because a century of engineering has shown that the most effective method is not this one.

Random thoughts.

Your power requirements exceed typical vehicular alternators by about 2X.

You don't want separate battery banks use one. Charge it while using it.

Use an engine driven hydraulic pack instead.

Consider using a hydraulic pump on the prime-mover and running quick connects back to provide the trailer hydraulics. Doing this electrically is going to be vastly more expensive, heavy, and troublesome.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

You're asking for literally, a truckload of batteries. Assuming 80 Ah batteries want draws of abour 4 A, you'd need 42 batteries to handle the peak draw. Even the "typical" draw requires 30 batteries.

Obviously, charging these batteries are going to be problematic as well.

TTFN

FAQ731-376

 

[jas165]

Thanks for the input. Agree with itsmoked about not being most effective method. Pony motor will be a provided option as well as prime mover pump. Unfortunately, many customers want the electric solution mentioned above.

Systems of this type have been around in Europe for decades. In fact, one reliable and well engineered system uses a 5.5 kW, 24 vdc motor and qty (2) 190 A-hr batteries in series.

The crux of the issue is duty cycle. Unfortunately, duty cycle is a function of driver inputs, external inputs, road conditions and so forth.

Say the duty cycle is such that the motor draws 120 amps for 30 seconds and the next 70 seconds there is no current draw. I wish to use the batteries to provide the 30 seconds worth of current and then hope to have enough charge current to replenish the batteries during the off time.

Readily available commercial solutions include a 20 A 3-stage charger or a 55 A DC-DC converter. Looking for tips regarding a charging system for duty cycle above.

 

[IRstuff]

The current draw you describe isn't that far from the starting current on a large vehicle, but the duty cycle is a bit short for charging at a reasonable rate.

But, since this configuration could allow you to use only a single, heavy-duty battery, or two of them stacked, your customers might tolerate a short operating life, with the rapid charging cycle imposed. Your duty cycle would require charging at 52 amps, which is less than 30% of rated capacity, assuming 190Ah.

TTFN

FAQ731-376

 

[itsmoked]

Consider using a much, much smaller system with a hydraulic accumulator. This allows an 'average' pump pack to run nearly continuously while allowing large momentary load demands. This could nix the need for ANY batteries and their cycle life, and charge profile issues.

Keith Cress
kcress -

http://www.flaminsystems.com