Direct Power 4, Self Powered PV SSR Control For Direct Connect Water Heater Element

This circuit will power the control of direct connect PV water heater using a solid state relay, a 5V cell phone charger and an 18650 lithium battery. Most arrays will be above 60V and that is enough to power most cell phone chargers. The 4.2V battery is enough to power the 3-32V SSR and prevent it from entering the 2V region in the early morning which will destroy it from overheating. Most relays draw from 5 to 10ma, a minimal load for the battery. Cell phone chargers are about 5.2V and that voltage must be lowered not to exceed 4.2V on the battery. Two diodes in series drop the voltage approximately 1.4V. That ensures the battery won't drop below 3.7V. A 27 ohm resistor across one of the diodes provides a little extra current to get the battery voltage above 4V. Old 18650 batteries are easy to find in old battery packs and everyone has an old cell phone charger. This makes an easy power source for a solid state relay.

[@opera5714]

This circuit will power the control of direct connect PV water heater using a solid state relay, a 5V cell phone charger and an 18650 lithium battery. Most arrays will be above 60V and that is enough to power most cell phone chargers. The 4.2V battery is enough to power the 3-32V SSR and prevent it from entering the 2V region in the early morning which will destroy it from overheating. Most relays draw from 5 to 10ma, a minimal load for the battery. Cell phone chargers are about 5.2V and that voltage must be lowered not to exceed 4.2V on the battery. Two diodes in series drop the voltage approximately 1.4V. That ensures the battery won't drop below 3.7V. A 27 ohm resistor across one of the diodes provides a little extra current to get the battery voltage above 4V. Old 18650 batteries are easy to find in old battery packs and everyone has an old cell phone charger. This makes an easy power source for a solid state relay.

[@cgmarch2359]

For better protection of that battery.. maybe add 1s bms on the cell? I am thinking in case the 5v supply fails and puts 10v . Anyway keep posting videos , I enjoy them:)

[@opera5714]

The solar community is technically challenged. Two diodes and a resistor may be a bridge too far. I tried to keep this cheap and simple with a linear thought process, wall wart > battery > SSR. Having a delta with wall wart and battery both feeding SSR thru diodes would be too confusing. I run dual Li for years with no balancing to keep power meters alive with low voltage on PV.

[@cgmarch2359]

I understand
I really like your videos because it shows outside the box thinking. Btw.. do you have a Makita wall charger like DC18SD ? Can you fivure how to power it with say 24V? I think it would be a good thing to figure that ..