I am building a new 12V DC switch panel for my boat and have a load of
switches rated at 10A@125V or 8A@240V. Although they have 12V
illumination there is not a DC rating in the datasheet. Does anyone have
any idea what sort of rating can I assume for low DC voltage or are they
totally unsuitable?

The switches are Cherry RRA22H3BBRHN rocker switches.

Thanks in advance,

Steve

On Mon, 06 Sep 2004 20:04:20 +1200, Steve wrote:

I am building a new 12V DC switch panel for my boat and have a load of
switches rated at 10A@125V or 8A@240V. Although they have 12V
illumination there is not a DC rating in the datasheet. Does anyone have
any idea what sort of rating can I assume for low DC voltage or are they
totally unsuitable?

The switches are Cherry RRA22H3BBRHN rocker switches.

Thanks in advance,

Steve

I've always been told to use DC switches and breakers on DC.
The arc is harder to break because there isn't a null period in DC
like there is in AC.
I wouldn't use them unless they are rated for Direct Current.
Mark E. Williams

Went around on this on some microswitches a while back. Basically it
appeared that low voltage DC (less than 28 volts) had higher ratings than
AC. I think that is the general rule. It is pretty well safe if it is a
snap action switch. At higher DC voltage it is a nono. Too much arc. Take
one load it up twice max current and run it a couple of hundred times. Then
bust it open and look at the contacts. You will know if it is OK.

Jim



"Steve" wrote in message
news
I am building a new 12V DC switch panel for my boat and have a load of
switches rated at 10A@125V or 8A@240V. Although they have 12V
illumination there is not a DC rating in the datasheet. Does anyone have
any idea what sort of rating can I assume for low DC voltage or are they
totally unsuitable?

The switches are Cherry RRA22H3BBRHN rocker switches.

Thanks in advance,

Steve

Maynard G. Krebbs wrote:

On Mon, 06 Sep 2004 20:04:20 +1200, Steve wrote:


I am building a new 12V DC switch panel for my boat and have a load of
switches rated at 10A@125V or 8A@240V. Although they have 12V
illumination there is not a DC rating in the datasheet. Does anyone have
any idea what sort of rating can I assume for low DC voltage or are they
totally unsuitable?

The switches are Cherry RRA22H3BBRHN rocker switches.

Thanks in advance,

Steve


I've always been told to use DC switches and breakers on DC.
The arc is harder to break because there isn't a null period in DC
like there is in AC.
I wouldn't use them unless they are rated for Direct Current.
Mark E. Williams

One way to help switches in DC circuits is to connect a capacitor
across the switch. It sucks up the last bit of current as the
switch opens, helping to prevent the formation of an arc. Fast
acting 'snap' switches last better in DC. A few microfarads,
properly polarised (positive towards the positive battery) can work
wonders. I would try your switches, make them changeable and carry
a spare for critical applications. They may survive the duty and
conditions you throw at them, if not, go upscale. Try one. Work it
to death. The rating is only intended to indicate safe working
current, not indicative of arc tolerance, which usually means
beefier contact and actuator design, heavier case, toggle, etc.

A shorted arc suppression capacitor becomes a stuck 'on' switch in
circuit.

DC and inductors like solenoids are a bitch on switches. A starter
switch comes to mind as possibly the most critical. But, remote
switching is only a luxury, non? There is always the modified hammer
tool for jumping starter solenoids.

A few wire nuts aboard, or even electrical tape can save an
electrically challenging day.

Terry K

I had thought about the capacitor but wasn't sure if it would help much
with the really big current loads which are all motors (bilge, toilet,
fresh water, gray discharge etc.). Would a 100uF cap actually be enough
to cope with such a large inductive load?

The steady state load for all the inductive loads is around 7 amps with
obviously a initially high startup load (around 10+ amps). From the
postings I get the impression that it is breaking the circuit that is
the issue with current rating and in these cases the norm current will
be well below the 125V AC rated current.

The mainly resistive loads (halogen lighting) has a high startup current
also when cold. A cap could help here I guess.

I guess I will try them and see how it goes. The only real reason I want
to use these is that they are round and therefore easy to mount in a panel.

Thanks for you help everyone.


Steve

"Steve" wrote in message
...
I had thought about the capacitor but wasn't sure if it would help much
with the really big current loads which are all motors (bilge, toilet,
fresh water, gray discharge etc.). Would a 100uF cap actually be enough
to cope with such a large inductive load?

That is way to high. Use 1uF at most, together with a series resistor of 10
ohm or so. Having a large capacitor will kill the switch when closing. The
loaded cap gets shorted....

In a DC system, you can also put a diode across the switch, in reverse. It
blocks the current from the battery TO the load, but any induction which
creates the opposite voltage across the switch, opens the diode and prevents
any arcing.

Meindert

I may be a little late with this reply but you know you can conduct 10amps
in the switch. The switching of DC is the issue. In the olden days when caps
were added across ignition points to keep the points from arcing and eating
the energy that is supposed to make sparks. They used a 0.22 uf cap to keep
8 amps or so from causing a the slow moving points from arcing. To be safe
I would suggest using a 100v minimum ceramic is best but an electrolytic
will do. The value should be about 1 to 2 uf and to be super safe a series
diode 2 amps average is ok in series with the cap. The anode of the diode
should be at the + end of the switch and the cathode connected to the + end
of the cap. Also a resistor must be added across the diode of 10 to 330 ohms
at 1/2 watt for lead strength. This series string of cap and diode and
resistor in parallel are across the switch terminals. This should protect
the switch.

Good luck Ray





"Terry Spragg" wrote in message
...
Maynard G. Krebbs wrote:

On Mon, 06 Sep 2004 20:04:20 +1200, Steve wrote:


I am building a new 12V DC switch panel for my boat and have a load of
switches rated at 10A@125V or 8A@240V. Although they have 12V
illumination there is not a DC rating in the datasheet. Does anyone have
any idea what sort of rating can I assume for low DC voltage or are they
totally unsuitable?

The switches are Cherry RRA22H3BBRHN rocker switches.

Thanks in advance,

Steve


I've always been told to use DC switches and breakers on DC.
The arc is harder to break because there isn't a null period in DC
like there is in AC.
I wouldn't use them unless they are rated for Direct Current.
Mark E. Williams

One way to help switches in DC circuits is to connect a capacitor
across the switch. It sucks up the last bit of current as the
switch opens, helping to prevent the formation of an arc. Fast
acting 'snap' switches last better in DC. A few microfarads,
properly polarised (positive towards the positive battery) can work
wonders. I would try your switches, make them changeable and carry
a spare for critical applications. They may survive the duty and
conditions you throw at them, if not, go upscale. Try one. Work it
to death. The rating is only intended to indicate safe working
current, not indicative of arc tolerance, which usually means
beefier contact and actuator design, heavier case, toggle, etc.

A shorted arc suppression capacitor becomes a stuck 'on' switch in
circuit.

DC and inductors like solenoids are a bitch on switches. A starter
switch comes to mind as possibly the most critical. But, remote
switching is only a luxury, non? There is always the modified hammer
tool for jumping starter solenoids.

A few wire nuts aboard, or even electrical tape can save an
electrically challenging day.

Terry K