I have started working on a wireless meter for my solar system. You can read about it here:
http://osaether.wordpress.com/

I just had a look at the datasheet for the nRF24LE1, and it seems like a very interesting unit. The USB dongle is very tiny as well. Im looking forward to see how this project goes.

BTW, Doesnt the morning star already make a remote meter for the sunsaver mppt?
Also, how are you going to read the data from the serial line? do you know the baud rates, syntax etc...??

TonyB wrote:I just had a look at the datasheet for the nRF24LE1, and it seems like a very interesting unit. The USB dongle is very tiny as well. Im looking forward to see how this project goes.

BTW, Doesnt the morning star already make a remote meter for the sunsaver mppt?
Also, how are you going to read the data from the serial line? do you know the baud rates, syntax etc...??

Yes morningstar already make a remote meter but it is wired and does not give the total current in and out of the batteries. The serial line protocol used as well as baud rate and so on is described in detail in these documents: SunSaver MPPT MODBUS Document and PC Meterbus Instructions available on the Morningstar web site.

Regards,
Ole

Hi OS,

You shouldn't need any more than 12bits resolution. With 12 bits you can measure up to 40 amps with 10mA resolution. the important thing is that you need a good current amplifier. Please have a look at this thread: current-sensing-t107.html i just updated it.

Sensing current on the low side is even easier, but it breaks the ground line. If you want to do that, look at the low side current sensing document.

cheers.

TonyB wrote:Hi OS,

You shouldn't need any more than 12bits resolution. With 12 bits you can measure up to 40 amps with 10mA resolution. the important thing is that you need a good current amplifier. Please have a look at this thread: current-sensing-t107.html i just updated it.

Sensing current on the low side is even easier, but it breaks the ground line. If you want to do that, look at the low side current sensing document.

cheers.

Hi Tony,

Thanks for pointing me in the right direction. The Trimetric shunt is in series with the minus terminal of my battey so I guess the low side method is the way to go. Can this method be used to measure both positive and negative currents? The Trimetric shunt is 1mV per ampere and I want to measure as much as +/- 100A in steps of 10mA so maybe I need another method?

I also see that the method used requires a +/- voltage supply. Does this mean I need some kind of DC/DC converter to generate the +/- supply from my 12V batteries?

Regards,
Ole

Hello OS,

To measure current in both forward and reverse, you will need a +/- supply.
You can easily use a reverse voltage charge pump to supply your negative rail.

If your measuring current in the forward direction only, all you need is an amplifier with with a common mode input ranging to ground, similar to the lt1013, or the lt2050.

To measure current in reverse, all you need is another amplifier, with inputs connected the other way around.

This way, you will have one amplifier with an output voltage proportional to the forward current, and another amplifier output with a voltage proportional to the reverse current.

Thanks.