Power Supply Voltage

[Mumbles]

I’m going thru some old chargers to try and find a 7.5 volt charger to try and use in my newly acquired Merc O Tronic 98 but while checking the output on some, I noticed the output voltage was much higher than what they are rated at. Has anyone else noticed this and will the voltage come down when a load is applied to the charger? I’d sure hate to fry the workings in the 98. 😕

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[nj-boatbuilder57]

Look at the center picture. It doesn’t simply say 7.5VDC on the label…..it says 7.5VDC while 1.5A is being drawn. You’re taking a reading at "no load"……were you to draw 1.5A, the voltage would fall to the advertised 7.5VDC.

I can’t read the other labels, but I’m sure it’s the same situation: you’re not reading "loaded" voltage, but rather no-load voltage.

The degree to which the advertised loaded voltage goes up during a no-load voltage is called "regulation", and depending on the design of the power supply can vary from perfect regulation where no-load voltage = loaded voltage (best) to absolutely dismal regulation where the NLV skyrockets.(worst).

The follow-up question is, of course, "can these be used in your application?", and to know that, you need to know not only the voltage requirement of your application but also how much current your application will draw. That is a key factor.

[PugetSoundBoater]

Would it be possible to plug the charger into a device like it was designed for, and somehow tap into the wiring of the chargers cord that fits into the device. Attach your meter to the taped into wiring between charger and device.

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

[Mumbles]

OK, so what about something like this one which is posted in another thread? It’s rated at 7.5 VDC and 5.34 Amps. What would the no load voltage be on it and just how much current do the 98’s draw?

https://www.ebay.com/itm/1-X-GS40A07-P1 … SwyXNZ8HdO

viewtopic.php?f=2&t=18181&hilit=power+supply

PSB: Yeah, your idea could be done but the phones and cameras etc. these things powered have been long gone!

[nj-boatbuilder57]

The unit in that eBay link is a switcher powersupply. It has full electronic regulation, so the output voltage will be pretty stable from no-load to full load.

But to your other (more important) question: "what does a 98 draw?" No idea…..but the specs should be on the item near the power supply connection. Is there any sort of labeling that indicates such? Or do you have an owner’s manual that states the power requirements? Don’t buy any power supplies until that is known…

[mercuryman]

On my Mercotonic while testing a Bendix coil the amp meter shows 3 when the rheostat is turned full right. The coils spark jumps the gap around 2 amps.

[nj-boatbuilder57]

…but what it draws from its power source may, in fact, be quite a bit different.

[RICHARD A. WHITE]

I recognize that power supply!!!!… But that one is from England??????

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[dave-bernard]

just get a 7.2V battery and charger for radio controlled toys . works just fine. done many. cost, about $35.00 or less

[mercuryman]

Just did a test with amp meter connected to 7.2 volt battery I am pulling about 6 amps from battery with rheostat full right.

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