Hi there,
I want to connect 10 panels. Two sets in serie, en those two sets then in parrallel.
Is the smartsolar MMTP 250/70 tr the best choice ?
Or should i install two smaller chargers ?
Many thanks
asked
One 250/70 or two smaller units ?
@Kris Goubert Sure why not, 5 series x 2 parallel fits comfortably within the 250-70 specs.
A 5 series string has a Voc of 221v @ -15c.
The Isc from the 2 strings is 22.62a, under the Max. PV short circuit current limit of 35a.
Array power of 3550w is under the mppt's nominal 4000w limit, for a 48v battery.
2 strings paralleled wont require string fusing (unless local regulations require it).
I agree with @klim8skeptic that a single 250/70 sounds like the best plan for all the reasons given above. For contrast though, I'm in a slightly different situation because I'm installing 16 panels of 425w each. My panels have a Voc of 49.9V (higher at low temps) and Isc of 10.74A.
So, 16 panels can only be divided up into 8 x 2 or 4 x 4. If I went with 8 series, 2 parallel then my voltage would be over 400V and if I went with 4 series and 4 parallel then my short circuit current would be too high and would require string fusing and combiner boxes etc. So I've decided to buy two 250/60 MPPTs and split my array into two 4 series, 2 parallel arrays. That way I don't need string fusing and I'm well within all the other limits. It also means I have some resiliency in case of failure of one half of my array. I could have gone with an RS 450/100 for slightly less cost but the 100A charge limit is a bit lower than 2 x 60A, and I would not have the resiliency of two independent arrays.
In your case, 10 panels can only divide into 2 x 5 or 5 x 2 and the obvious way to go is 5 series, 2 parallel to avoid string fusing and fit nicely within the 250V Voc limit.
I have been running this exact arrangement for a week. 5 in series and two strings parallel to a 250/70. Works great!
