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Old 13-04-2021, 09:06   #1
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How to calculate DC switch amperage if AC amperage is known ?

On body of rocker switch is stated:
6 A 250 V AC
10 A 125 V AC.
I bought switch as 16 A, 12 DC.

https://www.ebay.co.uk/itm/1X-12V-16...A/383828084794

Any formula to calculate DC amperage?

When i connected switch to 12V DC, it does not illuminate (LED).
It seems to me, it illuminate just if connected to AC ( I did not try)?
Tnx
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Old 13-04-2021, 09:49   #2
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Re: How to calculate DC switch amperage if AC amperage is known ?

There is no simple conversion for converting the amperage rating of an AC switch to DC. It can be dramatically lower because of the difficulty in breaking a DC current especially if connected to an inductive load. Many switches that work well on AC are not recommended at all for DC switching. DC switch amperage ratings are almost NEVER higher than the AC ratings.

If the switch is actually designed and rated for 10A at 120VAC I would bet it will have a very short life switching 16 amps of 12V.

Based on the rating of the switch, I would expect the LED is for AC use only.

Welcome to the world of buying cheap junk from China. Quality, labeling, compliance, and ratings are a total crapshoot.
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Old 13-04-2021, 10:25   #3
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Re: How to calculate DC switch amperage if AC amperage is known ?

BillKny pretty much said it.
A 16A 12VDC rated switch should be so labelled.


"Carling" AC/DC ratings are followed by "V" only, without the letters AC and DC following. For example a 125V rating would be read as 125 volts AC and 125 volts DC.
DC Rule of Thumb

For those switches that list an AC voltage rating only, the "DC Rule of Thumb" can be applied for determining the switch's maximum DC current rating. This "rule" states the highest amperage on the switch should perform satisfactorily up to 30 volts DC. For example, a switch which is rated at 10A 250VAC; 15A 125VAC; 3/4HP 125-250VAC, will be likely to perform satisfactorily at 15 amps up to 30 volts DC (VDC).
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Old 13-04-2021, 10:46   #4
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Re: How to calculate DC switch amperage if AC amperage is known ?

It depends on the design of the switch. Some designs that are suitable for AC aren't suitable for DC, and some are. If there's no DC rating, the prudent thing is to use a different switch, especially for critical circuits.


The two main problems with AC switches being used on DC are that: 1) they may fail closed (on) due to contact welding, and 2) they will tend to have a short life.





Quote:
Originally Posted by GordMay View Post
For those switches that list an AC voltage rating only, the "DC Rule of Thumb" can be applied for determining the switch's maximum DC current rating. This "rule" states the highest amperage on the switch should perform satisfactorily up to 30 volts DC. For example, a switch which is rated at 10A 250VAC; 15A 125VAC; 3/4HP 125-250VAC, will be likely to perform satisfactorily at 15 amps up to 30 volts DC (VDC).


This is dangerous advice because it only applies to snap switches. Snap switches were once common but are now relatively rare.
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Old 13-04-2021, 11:00   #5
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Re: How to calculate DC switch amperage if AC amperage is known ?

Quote:
Originally Posted by BillKny View Post
There is no simple conversion for converting the amperage rating of an AC switch to DC. It can be dramatically lower because of the difficulty in breaking a DC current especially if connected to an inductive load. Many switches that work well on AC are not recommended at all for DC switching. DC switch amperage ratings are almost NEVER higher than the AC ratings.

If the switch is actually designed and rated for 10A at 120VAC I would bet it will have a very short life switching 16 amps of 12V.

Based on the rating of the switch, I would expect the LED is for AC use only.

Welcome to the world of buying cheap junk from China. Quality, labeling, compliance, and ratings are a total crapshoot.
I agree with Bill re the different contact demands when switching DC vs AC.

I will disagree about China... basically just about EVERYTHING is made in China, so the job is to be careful when selecting and purchasing things. I've had good results with most of my ordering - they even resend if something went missing in the post - and I complain if something's wrong. If the switch was alleged to be 16A@12vDC, but the body is just marked "6 A 250 V AC, 10 A 125 V AC" - it's the wrong switch. Complain about it and claim a refund. They will do about anything to avoid a bad review.

Is your DC load going to be close to 16A? If it's actually under 10A, and not inductive (eg not a motorized thing), that particular switch might be OK.
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Old 13-04-2021, 11:26   #6
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Re: How to calculate DC switch amperage if AC amperage is known ?

My previous post quoted Carling Technologies’ “Switch Learn More Pages”.
Specifically, “Amp Ratings, HP, Volts”
https://www.carlingtech.com/amp-hp-volts
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Old 13-04-2021, 12:02   #7
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Re: How to calculate DC switch amperage if AC amperage is known ?

Another boat here in the anchorage has had consistent problems with 12v illuminated rocker switches. They are "rated" a 10A, but fail annually when used to switch a propane solenoid which draws less than 1 amp. A good 10A DC switch is a whole different thing than an 10A AC switch.
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Old 14-04-2021, 08:12   #8
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Re: How to calculate DC switch amperage if AC amperage is known ?

Quote:
Originally Posted by squaw999 View Post
On body of rocker switch is stated:
6 A 250 V AC
10 A 125 V AC.
I bought switch as 16 A, 12 DC.

https://www.ebay.co.uk/itm/1X-12V-16...A/383828084794

Any formula to calculate DC amperage?

When i connected switch to 12V DC, it does not illuminate (LED).
It seems to me, it illuminate just if connected to AC ( I did not try)?
Tnx
I believe it is apples and oranges similar to relays. The shape of the contact surfaces are different since DC arcs where as AC is self quenching.
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Old 14-04-2021, 08:24   #9
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Re: How to calculate DC switch amperage if AC amperage is known ?

Looking at the ad, I think you were sent the wrong switch. This is very explicitly advertised as a 12V switch. Current rating aside, you should not expect an LED in a 120V switch to work at 12V.
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Old 14-04-2021, 08:31   #10
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Re: How to calculate DC switch amperage if AC amperage is known ?

With this switch, I was planning to turn off/on 2 solar panels (2 x 100 W).
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Old 14-04-2021, 09:46   #11
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Re: How to calculate DC switch amperage if AC amperage is known ?

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Originally Posted by squaw999 View Post
With this switch, I was planning to turn off/on 2 solar panels (2 x 100 W).
Use a DC circuit breaker of the appropriate rating - 20 or 25 amp.
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Old 14-04-2021, 09:55   #12
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Re: How to calculate DC switch amperage if AC amperage is known ?

The lower the voltage, the higher the amperage draw.
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Old 14-04-2021, 10:04   #13
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Re: How to calculate DC switch amperage if AC amperage is known ?

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Originally Posted by MV Caroline View Post
The lower the voltage, the higher the amperage draw.
Yes, for the same wattage. Not so for switches. Since the resistance of a closed switch is ideally near zero it all comes down to current.

Just like a 10 amp 120 volt fuse is still 10 amps at 12 volts, not 100 amps.
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Old 14-04-2021, 10:24   #14
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Re: How to calculate DC switch amperage if AC amperage is known ?

Lets make it simple. You have the wrong switch for your application. Write it off and buy the correct switch.
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Old 14-04-2021, 10:42   #15
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Re: How to calculate DC switch amperage if AC amperage is known ?

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Originally Posted by MV Carolin,e View Post
The lower the voltage, the higher the amperage draw.
Not really sure as to what you are eluding to.
Basic electricity formulas are set in gold:
I = current in amps is equal to Voltage E divided by Resistance in Ohms.


I = E/R more commonly expressed as E = IR



After some thought. I believe that the the common idea that Lower voltage raises current is due to inductive motor theory (a very complex inductive magnetic function) where a stalled motor draws maximum current and an unloaded running motor draws little current and in many applications the motor stalls due to overloading. Causing voltage input at the motor to decrease and causing the stall to get worse, which in some cases will blow breakers or burn out the motor.

BUT in basic DC electronics theory 1 Volt with a 1 Ohm load would be a 1 Amp current. So 2 V with a 1 Ohm load would be 2 Amps of Current therefor Current is directly proportional to Voltage.
I have been in electronics since my 1959 Junior High days where I finally discovered why my flash light produced a light from a Carbon Zinc device.

Slow day around here.
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