I have a blue solar charger 75/15 mppt installed. I have 2 solar pannels they give me on the moment 27V (not connected). Normaly, if the voltage is 5V higher than the batteryvoktage ( in my case 12,4V) the charger have to charge my battery's. But it doesn't. If i connect the pannels on the charger i have 12,4V on the connectionsrews, not the 27V before. Wath is rong??