Especially problematic are appliances that try to control their heat
or have protection mechanisms (for example against overheating) that you
need to
be able to rely  on, such as an overheat protection switch or fuse,
or a simple thermostat contact.
Those were all designed for AC. Run them on DC and you will get into

I witnessed this problem early on when using a soldering iron that was
designed to
be run on a 24V transformer and has a built-in thremostat. Think the
popular Weller
soldering stations.
I had installed a 24V solar panel and wanted to show off that I could
solder powered by the sun.

It worked, I could easily solder the thick wires that I was using for
the installation of more
solar panels.
But I also noticed that a few seconds after I did some soldering, there
was a hiss from the iron.
I listened more closely and hear the familiar faint click - clack from
the iron's thermostat,
followed by a hiss that lasted almost a second.
So - even at 24V (open circuit Voltage around 35V) this thermostat was
not able to reliably
open its contacts on DC current.
I quickly disconnected the iron after that first use and only ran it on
AC from then on.

If you *need* to run an AC appliance on DC, make sure that *all*
possible ways the circuit can be
interrupted are done so in a way that was designed for DC or uses very
low current.
For example, if you have a hand switch as well as a thermostat and an
over-heating protection that 
all need to be able to switch off an appliance, then use a single DC
rated contactor (relay)
and place the switch, thermostat and over-heating protection all in
series in the *coil* circuit
of the contactor (relay) with appropriate surge protection (Zener
When the appliance needs to turn off, its tiny coil current is
interrupted, which turns the contactor off
and that interrupts the DC current to the appliance without a destroying
The coil is best run on AC or low voltage - even a PWM (50% duty cycle)
DC signal will allow turn off of
any arc that happens on the coil side of the contactor.

NOTE that a fuse should *not* be moved to the coil circuit, as it
depends on the current through the
appliance to turn off to protect from a fire through short circuit or
You must convert an in-circuit fuse to DC rating, that is the only way
to keep this safety feature.
Hope this gives some ideas.

-----Original Message-----
From: EV [] On Behalf Of Bill Dube via
Sent: Sunday, July 09, 2017 10:16 AM
Subject: Re: [EVDL] 120 volts items powered by pack voltage

Even though you can run these devices on DC, the switches on these
appliances are not suitable for DC, only AC. You risk a fire.
You can close the switch just fine on, say, your hairdryer, but when you
attempt to turn it "off", the DC will often simply arc across the
switch, and current will continue to flow. This arc will start a fire.

AC turns off and switches polarity 120 times per second, which
extinguishes the arc when switches and fuses open. DC is steady with not
breaks or reversals.

You get a small warning when this happens. The switch will make a small
"hiss" and the appliance only partially shuts off. Turn the switch back
on and pull the plug. There will be an arc at the plug and you may avert
a fire. The switch is typically toast, however.

DIY EV conversions often ran into this problem. Folks would (attempt to)
use a hairdryer for heat and defrost. They would get more heat than they
bargained for when they tried to switch it off. :-)

Bill D.

On 7/9/2017 5:27 AM, ken via EV wrote:
>   I have 2 scooter s 22 and 24 cells. I hocked onto the pack with 120 
> volt plug in . I was very please to find out I could run 120 led 
> bulbs, 120 volt motors with cumutators, like drill, skill saw, jig 
> saw, hair dryer, etc... !!
> Caution! watch your pack voltage and use the power tools LIGHTLY as 
> the voltage is lower and could burn out motors. this count be a great 
> emerency helper!!  and a led bulb could run for weeks . Even the old 
> compack flouresnt bulbs ran fine.
> _______________________________________________
> Read EVAngel's EV News at Please discuss EV drag

> racing at NEDRA (

Read EVAngel's EV News at Please discuss EV drag
racing at NEDRA (

Read EVAngel's EV News at
Please discuss EV drag racing at NEDRA (

Reply via email to