Current amplifier for variable speed motor?

[hotponyshoes]

You might want to put an ameter in line because the sort of current you mentioned seams very high !
I work on kit that uses a lot of 24v dc peristaltic pumps and they are each fuse protected by a 630ma fuse!

There is a 2a glass fuse for the existing pump.
I'm not sure if that just protects the pump or the whole pcb (that runs some led lights as well)

The machine chucks the error code before the fuse blows.

The bigger pump might not be as much as I think but it's more than the machine will handle.
It might well be engineered like this deliberately as they want an awful lot of money to set it up for a bigger pump...

 

[mike 109444]

With the pumps we use they have either a fixed ruin time (adjustable in settings) to dose a set amound of detergent or disinfectant or they pump wash fluid through the channels of an endoscope and have pressure sensors to turn off or on the individual pumps as they sens a certian pressure point. The pumps are either on or off not speed controlled.
Why do you need to control the speed ?

 

[hotponyshoes]

With the pumps we use they have either a fixed ruin time (adjustable in settings) to dose a set amound of detergent or disinfectant or they pump wash fluid through the channels of an endoscope and have pressure sensors to turn off or on the individual pumps as they sens a certian pressure point. The pumps are either on or off not speed controlled.
Why do you need to control the speed ?

This is on an arthroscope (basically the same thing as an endoscope)

Fluid is pumped down the channel to flush a joint. The speed is variable so you can control the flushing, open the joint, reduce for a clearer view, etc. You can also control the orifice shape/size to change from flushing to cutting.
This machine came out of a small animal (dogs/cats) practice and has had the working end changed to an equine version.
That's quite a bit bigger and the flow rate is not good enough hence the need to add the correct/matching pump for the hand piece

 

[mike 109444]

The way we check the output of an individual channel on our washers is by measuring the volume of liquid output into a measuring cylinder over a minute. the two speeds of channel pump we use output 50ml for slow pump and 440ml for fast pump. This can be changed a bit by chaning the size of the pump tube (3.2 to 4.8 id). The speed of the pump motor stays the same between a slow pump and a fast pump, it's the gearbox of the pump assembly that differs. 48rpm ver 310rpm.
It might be worth measuring the quantity that the current pumpS outputs then try changing the pump tube for a larger bore pipe. Unsure if this would increase your flow rate enough.

 

[hotponyshoes]

The varying flow rate is a quite necessary part of the operating on this

 

[sako243]

The circuit @voipio drew will work but most MOSFETs won't allow a gate voltage above say 20V typically so you'll need a voltage divider on the input.

This MOSFET would do. A 2:1 or similar voltage divider would work so say a 20k and a 10k resistor connected in series between your controller output and ground with the MOSFET fed from the centre tap.

Infineon HEXFET N-Channel MOSFET, 100 A, 40 V TO-220AB IRF1104PBF | RS

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