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simple PV low-power relay

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Alby_K

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Hi guys, I am new to all of this, in fact I started digging yesterday, so forgive my poor diagram :meh:.
Mission: I want to built a small solar powered light arrangement, that turns on automatically after dusk.
Currenctly I have battery packs (BP) hooked up to a solar pad (SP) via USB and there is a USB lamp that somebody can plug-in. Now I want to 'automate that', based on the following requirements:
1) everything is connected and no manual switching or pluggin-in has to be performed
2) the battery packs cannot be charged while being connected to a load
3) minimal power consumption of components

So I thought about connecting the 5Vout of the BP to a 5V relay (Photodiode is the signal) and then to a buck converter to finally power the usually 1.2V-battery-powered LED string lights. The relay runs NC mode and opens the circuit once it's sunny outside. However, the relay also has to close the SP-BP connected circuit once it's sunny and this is were my diagram has problems. I think I cannot connect both the SP and BP to the common terminal (can I?o_O).
The relay I found eats roughly 150mA, which is ok because I will use a 20.000mAh battery pack. But I really don't want to use 2 relays - one for the BP-circuit and the other for the SP circuit, since it will eat 300mA*5V=1.5W which is too much for my effectively 13W DC SP. I don't want to use over 10% of the generated Power just to maintain relays...
Is there something like selector switch relay with 4 connections, that can switch back and forth between 1-2 and 3-4? Ideally even a latching type?
Thanks guys! :woot:
 

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spec

Well-Known Member
Most Helpful Member
Hi guys, I am new to all of this, in fact I started digging yesterday, so forgive my diagram :meh:.
Mission: I want to built a small solar powered light arrangement, that turns on automatically after dusk.
Currenctly I have battery packs (BP) hooked up to a solar pad (SP) via USB and there is a USB lamp that somebody can plug-in. Now I want to 'automate that', based on the following requirements:
1) everything is connected and no manual switching or pluggin-in has to be performed
2) the battery packs cannot be charged while being connected to a load
3) minimal power consumption of components

So I thought about connecting the 5Vout of the BP to a 5V relay (Photodiode is the signal) and then to a buck converter to finally power the usually 1.2V-battery-powered LED string lights. The relay runs NC mode and opens the circuit once it's sunny outside. However, the relay also has to close the SP-BP connected circuit once it's sunny and this is were my diagram has problems. I think I cannot connect both the SP and BP to the common terminal (can I?o_O).
The relay I found eats roughly 150mA, which is ok because I will use a 20.000mAh battery pack. But I really don't want to use 2 relays - one for the BP-circuit and the other for the SP circuit, since it will eat 300mA*5V=1.5W which is too much for my effectively 13W DC SP. I don't want to use over 10% of the generated Power just to maintain relays...
Is there something like selector switch relay with 4 connections, that can switch back and forth between 1-2 and 3-4? Ideally even a latching type?
Thanks guys! :woot:
Hi Alby,

If I understand your requirement correctly, it would not be necessary to use a mechanical relay. Instead a MOSFET would be an ideal switch and would consume virtually no current. A MOSFET approach would probably cost less than a relay and a MOSFET would never wear out like a relay.

spec
 
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