Mechanical timer switch with 2 loads, load 1 constantly "on" until the timer is activated to turn on 2nd load

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WAGuy58

Member
Location
Edmonds, WA
Occupation
Contractor
I have a client that wants to add a solar powered light inside a shed 200+ feet from his house. He doesn't want to run a line to the shed. The shed doesn't have any windows and it is fairly dark during the day time which makes it difficult to locate smallish items on the shelves. He wants to be able to put a mechanical spring timer (15 min) inside the shed so he can turn the light on during the day and have it turn off automatically so it doesn't run down the batteries and leave the unit in an uncharged state.

Most solar outdoor/shed lights are motion activated and also have a photoelectric switch (PE) so that the light only comes on when it is dark outside. These units mount the PE switch on the solar collector unit which is mounted outside of the shed -- allowing it only to be operable at night. They incorporate the PE switch because they use 18650 lithium batteries which can get damaged if they are being charged and discharged at the same time. This is another reason why they put the PE switch outside.

Is there any such thing as a mechanical timer with two load terminals. with load 1 being continuous continuity (ie. in the battery charge state) until the timer is activated which switches the continuity to load 2 (the light)? The two loads must be mutually exclusive - essentially a SPDT switch.
 
This is borderline DIY, but also low voltage so the mods may allow it.

To answer the question you actually asked, the switch you are asking about exists as a catalog number. I've never actually bought one. The device is the intermatic FD32HW. But don't do this! (See below)
page 70,71. There are other part numbers with different maximum time amounts.
1753977791594.png

To answer the question you didn't ask:

It is physically impossible to simultaneously charge and discharge a 2 terminal device. This is not a question of possibly damaging the device, this is a question of physics. The electricity can't flow in two directions at once. If you have a light connected to a battery as well as a charger connected to that battery, when you turn on the light then some of the charge current will go to run the light, reducing the charge current going to the battery.

However if you have a light powered by a battery and a charger connected to that battery, then turning on the light might confuse the charger, and then the charger could damage the battery.

You don't need a switch to disconnect the charger from the battery when you want to use the light (in fact, that might also confuse the charger and damage the battery). Instead you need a battery and charge controller that is designed to handle the light getting turned on and off. Unfortunately that is the limit of my knowledge on the subject, so I can't recommend hardware.
 
winnie said:
This is borderline DIY, but also low voltage so the mods may allow it.

To answer the question you actually asked, the switch you are asking about exists as a catalog number. I've never actually bought one. The device is the intermatic FD32HW. But don't do this! (See below)
page 70,71. There are other part numbers with different maximum time amounts.
View attachment 2578875

To answer the question you didn't ask:

It is physically impossible to simultaneously charge and discharge a 2 terminal device. This is not a question of possibly damaging the device, this is a question of physics. The electricity can't flow in two directions at once. If you have a light connected to a battery as well as a charger connected to that battery, when you turn on the light then some of the charge current will go to run the light, reducing the charge current going to the battery.

However if you have a light powered by a battery and a charger connected to that battery, then turning on the light might confuse the charger, and then the charger could damage the battery.

You don't need a switch to disconnect the charger from the battery when you want to use the light (in fact, that might also confuse the charger and damage the battery). Instead you need a battery and charge controller that is designed to handle the light getting turned on and off. Unfortunately that is the limit of my knowledge on the subject, so I can't recommend hardware.
Click to expand...
Thank you for the quick response. I think I'll recommend that he keep a regular flashlight out there. ;^)
 
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