Relay between solar panel and buck converter

Account cancelled 2019-02-19 03:49:13 5319 Views4 Replies
I have a large extra solar panel (300W, 44V, 9A) that we will use to power a solar attic fan. But the fan is is rated at up to 38V, and to get the right fanspeed needs about 20V; it pulls about 3A, max. Since the panel provides 44V during the day I need to adjust the voltage. But since there is no battery the power supplied is unsteady at sunrise and sunset, which I believe will cause the buck to cycle on and off until the sun rises enough. Probably good to prevent that so am thinking of using a Raspberry Pi to control a relay that would connect the buck to the solar panel once there was enough light, and disconnect before sunset.

The Digital 16A Relay Module SKU:DFR0251 looks like it can easily handle the current and voltage (assuming I understand the spec: Maximum switching voltage: 400VAC(NO)). But seems like overkill for a 3A, 44V system.

The MOSFET Power Controller SKU:DFR0457 looks more appealing, but voltage rating looks insufficient:
VIN Operating Voltage: 5V-36V DC
VIN Operating Current: 0A-20A

Suggestions? Are there MOSFET conrollers that might work?

Thanks! {I note here that the fan is fine with power directly from a PV panel--its been doing that for years. I just want to feed it more power than the current 10W panel provides]

2019-02-20 17:39:14

robert.chen wrote: ↑
Wed Feb 20, 2019 8:08 am
Normally if using DC, 36V is enough, if you have 40V solar panel, you can consider to use the recommended module, it is enough to charge or power the system.

Thanks again, Robert! I appreciate your help. andromedag

2019-02-20 16:08:34 Normally if using DC, 36V is enough, if you have 40V solar panel, you can consider to use the recommended module, it is enough to charge or power the system. robert.chen

2019-02-20 15:47:30

robert.chen wrote: ↑
Tue Feb 19, 2019 2:54 am
44V DC is large DC current for open source hardware area, normally the max current for DC we use is 36V, you can consider to use a buck convert first before the relay, unfortunately, the max input buck module we have is 40V which is this one: https://edubirdie.com/research-proposal-writing-service may not be able to handle 44V.

Thanks for the suggestion. Because I've been trying to find a solution to this matter, and I wasn't able to find it. So you suggest using 44V or better 40V? andromedag

2019-02-19 10:54:21 44V DC is large DC current for open source hardware area, normally the max current for DC we use is 36V, you can consider to use a buck convert first before the relay, unfortunately, the max input buck module we have is 40V which is this one: https://www.dfrobot.com/product-1552.html may not be able to handle 44V. robert.chen