Hi. I have a second mppt 250 /70 max input 35 amp. I was ordering panels to suit. Trying to get the max power I could while staying under these figures. According to Ai which is constantly wrong . I need to dereg the 35 amp down to max 28 amp to cope with cloud spikes etc?. I’ve been running my other charger250 /60 very close to max with no issues except getting hot on certain days. However maybe I have been lucky. Looking for advice from seasoned blue solar users on what the max paramiters should be. Interested to hear from any one that has blown a unit which was in the correct paramiters. Cheers rob
Hi @Robbus
No need to use AI. Use the official tool.
The two rules of no overamping the input current limit (ISC not tracking amps) or the voltage (VOC) max at minimum temperatures are basically it for sizing.
I have had exactly two units blow and the installation was nowhere near the limit, but will add they were on the older 250/100 units from 2018 before the PV short relays were added. Nothing since and the replacements are just about to shift out of warranty on the same arrays as before.
Thanks for info . Didn’t know about relays. Do you know why you blow 2 units. Have you had your newer version trip the relays?
I have never used them for more than signal or very low loads.
Don’t go above 60% of their rating. That a decent safe margin
Programmable relay
DPST AC rating: 4A up to 240Vac / DC rating: 4A up to 35Vdc, 1A up to 60Vdc
mppt_calculator_03_09_2026_08_08_59.pdf (779.1 KB)
According to victron calculator these panels are ok.