Hello! This is my first post on the forum so forgive me if its posted in the wrong place, but here's my situation:

Im redoing the electric system in my off-grid summerhouse, where I have built a 24V LiFePO4 battery, will install a 24V fridge, inverter etc. My question is regarding the lights. I have found a bunch of 24V LED bulbs with standard types (E14, E27 etc) of sockets, for example: https://www.lamportillallt.se/sv/en...lagvoltslampa-2700k-450lm-e27-45w-12-24v.html The problem is that the fixture for these kind of bulbs are almost always rated for 220V AC (normal home mains) and I really struggle to find any lamps (meaning the actual thing you screw into the wall, cover, socket etc) that are made for 12V or 24V dc. My question is then, would it be possible to just buy a regular lamp with the matching socket type, e.g. E14, E27 etc, and then wire the live and neutral OR live and ground wires to my positive and negative terminals in the 24VDC system?
What would the hazards be of doing this? What kind of fuse should be used if its possible?

I welcome any tips, also other tips regarding lights in a 24V off grid system.

 

If I understand you correctly, you have lighting fixtures designed for 220V AC with standard sockets for bulbs. You also have 24V bulbs with bases that fit those sockets.

If this is correct, I see no problem with operating it off 24V.

Added: It could be exceeding the DC rating if the switch, but I would not think it would be a problem.

 

If I understand you correctly, you have lighting fixtures designed for 220V AC with standard sockets for bulbs. You also have 24V bulbs with bases that fit those sockets.

If this is correct, I see no problem with operating it off 24V.

Added: It could be exceeding the DC rating if the switch, but I would not think it would be a problem.

Ok thanks for the response! You understood my question correctly. Regarding the wiring, as I understand it most AC loads, like lamps, have 3 wires, live, neutral and ground/earth. Would it be best to connect live to the battery positive and neutral to battery negative? Would I skip the earth cable alltogether or have this connected to the battery negative as well?

 

Hello, and welcome to AAC.

Would it be best to connect live to the battery positive and neutral to battery negative?

Yes. This would keep things clear as to which line is positive and which line is negative.

Would I skip the earth cable alltogether or have this connected to the battery negative as well?

With 24VDC I wouldn't worry about grounding the housing. Low voltage does not present a shock hazard. Just ignore ground in this case.

 

Added: It could be exceeding the DC rating if the switch, but I would not think it would be a problem.

Good points. Switching DC is not the same as switching AC. You would think it is since it's just a make and break switch. However, there's a lot more going on when DC switches off. Draw more current than the switch is rated for on a DC voltage and you'll get an arc that will not extinguish until something burns down. But switching LED's generally doesn't draw much current. So I would think as @BobTPH is thinking there shouldn't be a problem. BUT then again we don't know how much DC current you're going to be switching.

 

Rethinking this. At 24V the switch is handling 10 times the AC current, and as Tony said, switching DC is harder on the switch than switching the same current at AC.

I would consider replacing the switch with one rated to handle the DC current you need.

 

Good points. Switching DC is not the same as switching AC. You would think it is since it's just a make and break switch. However, there's a lot more going on when DC switches off. Draw more current than the switch is rated for on a DC voltage and you'll get an arc that will not extinguish until something burns down. But switching LED's generally doesn't draw much current. So I would think as @BobTPH is thinking there shouldn't be a problem. BUT then again we don't know how much DC current you're going to be switching.

Right, good input from both. The LED bulbs I have in mind draw about 1.5-2.5W, meaning the current would be at max 2.5W/24V=0.1A if I calculate that correctly? Do you think that a regular 220V lamp with a built in switch "should" be able to handle that minimal current? Or am I better off finding a dedicated 24V rated switch?

 

0.1 amp (100mA) is probably not a problem for a standard light switch.

 

Here's why DC is hard on a switch:

[edit] rectifying and filtering AC results in an increased voltage of 1.414 times higher voltage. Still, shutting DC down does the same thing as the video shows. 220VAC rectified and filtered is 311.08 volts. A little misleading but nevertheless, switching DC is harder than AC. AC has zero voltage crossings 120 times per second, meaning any potential arcing is extinguished at any of those 120 moments.

 

Here's why DC is hard on a switch:

[edit] rectifying and filtering AC results in an increased voltage of 1.414 times higher voltage. Still, shutting DC down does the same thing as the video shows. 220VAC rectified and filtered is 311.08 volts. A little misleading but nevertheless, switching DC is harder than AC. AC has zero voltage crossings 120 times per second, meaning any potential arcing is extinguished at any of those 120 moments.

Haha a frightening example indeed, wouldnt want that going on on a wooden wall. Seems to be bit of a higher amperage draw in the video than 100mA but I will keep this in mind. Thanks

 

Right, good input from both. The LED bulbs I have in mind draw about 1.5-2.5W,

That is mot going to provide much light. A 60W equivalent LED bulb is about 8W.

 

That is mot going to provide much light. A 60W equivalent LED bulb is about 8W.

Its only for reding lights by the beds, I will have something brighter as a ceiling lamp, but go with a 24V DC dimmer for that one.

 

Then I think you are good to go.

 

Before becoming concerned with switches you really need to check and discover how much current the devices you are planning on using actually consume. While there are screw-in base light bulbs around, are they actually LED types, or are they older incandescent bulbs?? Low voltage lighting has been around for quite a while prior to the invention of LEDs. Not usually for home use though.
Revisiting post #1, I see that the replacements are indeed LED types. So the remaining concern will be polarity, because there is no guarantee that every fixture is wired the same. Reversed polarity is often damaging to semiconductor systems.
The 220 volt AC rating describes the insulation and spacing of the fixture and is a maximum value, nothing more. And all of the switches rated for AC operation are intended to handle the tungsten inrush of older lights, so there will be no problems there.

 

I use 11W 12V LED lamps in my caravan & the switches are 240V AC switches & never had any problem with them. On 24V your current draw would be about half.

 

I use 11W 12V LED lamps in my caravan & the switches are 240V AC switches & never had any problem with them. On 24V your current draw would be about half.

The effects are not necessarily immediate. It can cause the switches to wear out early.

 

The effects are not necessarily immediate. It can cause the switches to wear out early.

Certainly possible. The switches may not last more than 15 years, as opposed to the 30+ years when using 120 VAC on switches rated for 240 volts AC. Maybe that short a lifetime..

 

Certainly possible. The switches may not last more than 15 years, as opposed to the 30+ years when using 120 VAC on switches rated for 240 volts AC. Maybe that short a lifetime..

That is "Certainly possible." But we don't know the quality of the switch being used, nor do we know a switch will last 5 years, or 50 years. That's just speculation. But I respect all opinions whether I agree with them or not. I've had switches on 120VAC that were rated for 135VAC that lasted about 18 months. And they were switching LED can lighting. Each can light draws between 8 and 10 watts. Two of them in three years, so the 18 month is an estimate based on the fact that I didn't capture the information on exact time of failure.

 

Really, with switches it is far more important that the current rating be adequate. So the important question is the current rating, and we have no clue as to what that is.
Of the four AC light switches I grabbed off my shelf, two were rated 15 amps and two were rated at 20 amps. An 11 watt LED light at 24 volts will draw less than half an amp. The switches will wear out mechanically before the contacts show any problems.

 

Of the four AC light switches I grabbed off my shelf, two were rated 15 amps and two were rated at 20 amps. An 11 watt LED light at 24 volts will draw less than half an amp. The switches will wear out mechanically before the contacts show any problems.

The original lamp was 220V. Assuming a 60W bulb, that would be 272mA.

If they used a switch rated at say, 500mA AC, the DC rating would be less than that. So no, it is not at all obvious that it can handle the 24V DC current needed for 11W.

But the OP said he would be using a 1.5 to 2W bulb, so it is probably okay.