There are so many variables that I personally wouldn't have any idea of
where to start without knowing the exact application, environmental factors,
materials of construction, safety requirements, efficiency, etc., etc., etc., etc..
.
.
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t

on of the series runs was at 3.5A and another was 5.2A

Were both of those the same number of elements?
If so That corresponds to a huge change in resistance.
What is the material used in the heating elements?

 

What I need to really achieve is say 4A plus or minus half an Amp, running at the same voltage e.g 24V, if that makes sense

Nope, it is against the law, Ohm’s law. You cannot control both the current and the voltage on a variable resistance.

Bob

 

The following link might prove useful.

https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/4470.html

 

The power supply I am using is a constant current supply across the elements however due to the resistance differences they get loaded significantly differently.

Use for heating elements material with close to zero temperature resistance coefficient,
such as those, which used in instrument shunt.
For example - manganin (Cu 86%, Mn 12%, Ni 2%), working temperature up to 200°C.

 

Maybe a zoned approach? Have several zones and group your heaters and separate power lanes in these zones. You can have temperature readings from the zone and control the power for each zone to maintain temp in that zone. Probably look at circuitry for large reflow ovens for soldering boards. That, I think, would probably be closest to what you're doing?

 

If you're aiming for even temperature across a matrix of evenly-distributed heaters then you won't want the same power in each heater. The heaters near the centre of the matrix will lose less heat to the environment than those near/at the edge of the matrix. Think Antarctic penguin huddles.

 

Thanks you for all your replies, they are extremely helpful, and @dcbingaman thank you for that piece of reading material, this was along the lines of my initial though process on the matter by using a feedback method and @Danko for the materials input, i will have a look at this

 

the operating temperature wont exceed 100degC

Have you considered oil-filled radiator panels as you heat source? They can be custom-shaped and virtually any size.

 

There are electronic loads which can do constant I, V. power, R etc.

I don;t quite understand what your trying to do, but take a look at battery balancing IC's.

I almost think that you don't have as tight of a handle on the resistive elements and therefor you want to tweak them.

I think I agree with Alex that you may actually want to modify the power of each element and not necessarily make them the same.

 

Have you considered oil-filled radiator panels as you heat source? They can be custom-shaped and virtually any size.

I have considered similar options but the space i have to work with is very limited unfortunately

 

There are electronic loads which can do constant I, V. power, R etc.

I don;t quite understand what your trying to do, but take a look at battery balancing IC's.

I almost think that you don't have as tight of a handle on the resistive elements and therefor you want to tweak them.

I think I agree with Alex that you may actually want to modify the power of each element and not necessarily make them the same.

Thank you, i will have a look at the battery balancing IC's,

in essence you're right with the handle of the elements, as it stands im at the mercy of whatever the elements want to do in terms of their resistance when the temperature changes which then causes an imbalance which worsens as the temperature change increases

with Alex's comment i agree its just then needed to control the elements differently but this will be a ground up approach as i would need thermocouples all the way through to control that to, not against it by any stretch, just a lot more to account for and will need to change the controller out for something more substantial

 

the elements want to do in terms of their resistance when the temperature changes which then causes an imbalance which worsens as the temperature change increases

It should be the opposite. Heating elements increase their resistance as temperature rises, thus less current and less heating.

Edit: Actually I am wrong. If driven with constant voltage that would be true, with constant current it is as you ssid, higher resistance means more power to the element.

Bob

 

the space i have to work with is very limited unfortunately

Can you give us a ball-park figure?

 

Can you give us a ball-park figure?

around less than around 10 - 15mm height to fit a heat source in over a wide area