ajforsberg avatar image
ajforsberg asked

How to connect Smart solar MPPT 75/15 to an Argofet 100-3?

How to connect Smart solar MPPT 75/15 to an Argofet 100-3?

I have installed an Argofet to the 3 different batteries and would now like to install the Smart solar on the input of Argofet, is that possible or do I need to add some other device in between? If I only connect it to the input then will the MPPT be turned off.

MPPT ControllersArgo FET
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
einar avatar image
einar answered ·

The following method is tested and works for three battery banks, two AGM and one lithium bank. I’m not sure if this method will work if all battery banks are of the same type, but I don’t see why not.

My assumption is that the input of the Argofet when charging the batteries will have a voltage that is a little higher than the voltage of the battery bank with the lowest voltage.

To the battery bank that normally has the lowest voltage connect a timer with relay-function. This is important. Do not connect it to a lithium battery unless all battery banks are lithium. The timer must be possible to be programmed to second or minute on-time.

In addition to power for the timer connect 12V to one side of the relay and between the other side of the relay and the Argofet input, connect a resistor of 50-100 ohm / 0.25W in series with a diode. The diode oriented so that current can go only in direction of Argofet input.

The timer must be set to a minimum of 20 seconds to start Argofet and the solar charge controller. Start time should be when you think your solar panel will be able to generate enough to supply the Argofet and the solar charge unit. I used a minute timer and did set it to close the relay at 9:00 and open again at 9:01. The timer I used is called Cn101a (sold under different brands like Sinotimer / Oktimer / Baomain). Do not try the seconds timer Cn101s, it opens and closes the 0V line. Not the 12V line as described in the manual.

The timer is installed because it uses less energy than the Argofet and the solar charge controller. Also, if my other AGM battery should have a little lower voltage than the one supporting the Argofet input, current will only go to that that battery for 20 second per day. The rest of the day it will be disconnected, or the solar charge controller will supply power to the batteries.

If the battery supporting the Argofet input gets a voltage lower than about 10V it will not start the Argofet. If this happens the battery is defect, but nothing will happen with the other batteries. The diode prevents current to bypass the Argofet and go into the battery.

If another battery gets a voltage lower than 7V when using a 100-ohm resistor (or 9V for a 50 ohm resistor) the only thing that happens is that the resistor will burn, and the defect battery and the resistor must be replaced. ( 0.25W = U*U / R, if R=100 ohm then U = 5V and 12V – 5V = 7V).

To get hold of a resistor and a diode could be difficult unless you know someone working with electronics or there is a radio / TV repair shop in the neighbourhood. These are not sold in units of one, more likely 10 or 100.

NB! The resistor should not be made for more than 0.25W, because then you will empty the battery if another battery is defect.

NB! Make sure the diode is oriented correctly. If not the Argofet will not be turned on (just reverse it if this happens)

I couldn’t upload a wiring diagram, but if you need one you can contact me at

PS! Make sure you set the timer in Auto after programming it.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.