LPL/Saunders 4550XLG Enlarger power supply sparks

**scott jones** · 3-Jan-2004, 10:57

Hi Yall,

For the last three years that I have owned my Saunders 4550 XLG enlarger (which I love) I notice that sometimes the switch for the power supply emits a big blue spark when I turn it off. The power supply is also connectec to the Saunders ET500 timer. I notice that often if I turn off the timer first and wait awhile, then when I turn off the power supply, there is no spark.

The manufacturer of the power supply tells me he has not heard of this problem before, but the LPL did change the design of the power supply some time ago by putting a capacitor somehwere in the circuit, but he wasn't sure why. The US distributors of this enlarger have no knowledge of any of this.

So anyway, has anybody had a similar sparking problem with the switch to this power supply?

Thanks and Happy New Year

ScottJonesPhoto.com

**bob moulton** · 3-Jan-2004, 11:55

Scott: We bought the same enlarger at my school about two-three years ago. I have experienced identical problems with the power supply switch. The electrical spark is intermittent but still there. I have been unsuccessful in getting help from the distributor. That said, the unit works fine. I have the older model enlarger at home and love both. I guess one should just be grounded when turning the power supply off!

Bob

**Bob._3483** · 3-Jan-2004, 18:44

Can't really help with a solution as each case requires looking at individually, but it may (or may not....) be of interest to note that a spark when switching something off is caused by switching an inductive load (i.e. something with a coil in it). The sudden break in power through the coil causes a high voltage spike to flow through the circuit - too high for the switch to handle properly, hence the flashover as it switches.

Bob M's jest perpetrates a common (and dangerous) myth: the last thing you want to do is ground yourself! All you do then is provide the spike with a nice low resistance path to flow through YOU instead of the circuit! As a general point: never earth yourself around electricity - ever. The whole point of an earth (or "ground") is to supply a low resistance to the flow of current - so great a current flows that it trips the fuses or circuit breakers, hence cutting off the power. You do not want that current flow to be through you - you want it to be through the earthing of the equipment casing or the metal worktop etc.

A new switch will work for a while but unless you can find one that fits that is designed for inductive loads, the new one will soon start arcing over too.

Cheers,

**Ron Spencer** · 16-Mar-2004, 09:34

In addition to the second Bob's (not Bob M.) comment:

Bob is absolutely right!!! You should never be grounded around electrical circuits. Quite the opposite is true. It's best to be isolated by standing some on sort of insulating material such as a rubber mat. In a darkroom environment especially - since you're working with water and electricity in close proximity to one another, it's a good idea to install "GROUND FAULT CIRCUIT BREAKERS" to replace the regular ones in your breaker panel. Alternatively, if this is not possible, then replace your receptacles with "GROUND FAULT" receptacles. What a ground fault breaker or ground fault receptacle does is monitor any current flowing to ground (which indicates a short circuit in something that is plugged into that particular circuit) and will break or cut off the electricty to that circuit typically around 50 milliamps (if I recall correctly), which is not going to hurt you. Ground fault breakers or ground fault receptacles have a TEST button on them so you can periodically test them for proper operation.

Also, make sure that anything electrical in the darkroom is grounded. They should all have 3 prong plugs plugged into grounded receptacles (preferably ground fault units).

By the way, for those not familiar with ground fault receptacles - you can buy them at pretty much any hardware store.

Consult an electrician if you don't know how to do this yourself. If you incorrectly install either the ground fault breaker or ground fault receptacle it won't protect you!