Sargent 328 advice

1 have a 100w solar panel ,the current reading on my control panel are very  erratic, changing a couple of time's a second is this normal .would it be possible to fit an mppt controller in place of the built in controller or would it have to be re wired by passing the Sargent unit  

There is a discrete 2 channel solar controller located within the EC328 (and 325) Sargent box. It works well and doesn't need to be replaced unless faulty.

The current monitor in the 328 needs to be calibrated whenever the unit has been reset by changing battery, blown fuse, disconnecting controller, etc. Its best done in the dark with no solar activity (or you can throw a blanket over the panel) - instructions in the handbook.

This time of year, with just solar charging, it is not at all unusual to see erratic readings. If you switch a few lights on you should see a nice steady indication of discharge current.

I have almost exactly the same setup electrically - different vehicle and model but essentially the same components - and in weak sunlight conditions I see a similar pattern. It's almost certainly happening because the solar panel output is varying. This can lead to quite large changes in current if the voltage happens to be crossing the threshold for charging the battery.

I tend to ignore the current meter reading on the EC328 panel - firstly because it shows an aggregate of inputs and outputs, and secondly because it drifts a lot!

If you want a more accurate view of what the panel is doing, it is possible to fit an external display to the built-in solar controller like this:

https://www.ebay.co.uk/itm/222196123931/

But note that this requires physical access inside the EC328 - so fitting one is a little more than just "plug and play".

Thanks for replies,  very helpful