Polarity of DC adapters...can they cause problems?

Cheers Dave.

Frank,

I highly recommend you get a cheap multimeter. Most good hardware stores will have one. That way you can be sure rather than sorry and also it will come in handy all over the place. Most have functions for testing batteries etc. They can be got for as little as 5euro. However looking for one around the 20euro mark might be a better investment.

Frank,

I highly recommend you get a cheap multimeter. Most good hardware stores will have one. That way you can be sure rather than sorry and also it will come in handy all over the place. Most have functions for testing batteries etc. They can be got for as little as 5euro. However looking for one around the 20euro mark might be a better investment.

I agree with Dave, I never trust those weird little +/- symbols on power supply switches and mini-plugs. Even if there were a standard symbol, they're difficult to read and not necessarily logical. I picked up an adequate digital multimeter at peats for about 10 euro.

Since it is so easy to blow expensive electronic devices to heaven with misconfigured powersupplies, you might consider permanently installing a pair of diodes and a fuse at the input terminals of the device:

<--From power supply
[code:1]
fast fuse D2
-

---

~~~~~~~

---

|<

---

> To expensive device +
|
V D1
T
+

---

|

---

>To expensive device -
[/code:1]


The idea is that if you reverse the leads from the power supply, you hope the diode D1 will conduct and blow the fuse. Even if the fuse is slow, diode D2 should prevent any reverse current from getting to the device.

It won't give as much protection as a proper crowbar www.electronics-lab.com/projects/power/034/ circuit, but it's simple and may save your device.

The fact that expensive devices such as laptops, drive computers and digital cameras usually come without this 50 cent circuit says something about planned obsolesence or pennywise accounting or something!
.

Actually, if you just use the "bridge" part of the circuit (the four diodes arranged in a square) it will allow you to safely use whichever polarity is to hand.

So long, of course, that you wire up the output of the bridge correctly...

Actually, if you just use the "bridge" part of the circuit (the four diodes arranged in a square) it will allow you to safely use whichever polarity is to hand.

So long, of course, that you wire up the output of the bridge correctly...

Good point. The diode bridge and the fuse circuit above would both drop the input voltage a tiny bit, but most unregulated power supplies have a tolerance far above the 0.7V drop of a single silicon diode.

In all fairness, how much would it cost Meade to have a diode put into the circuit? Cents probably..... I just can't understand that kind of thinking, thier instruments have enough 'quirks' as it is.