# Odd Volt/Ohmeter readings



## DonR (Oct 18, 2012)

I was testing the new 300 LED strip recently
received...knew it needed 12 V DC...

Had 15 V dc available...using the rule;
a volt drop per 50 ohms needed 150 ohm apprx resistor
to get 12 V. Didn't have it so subbed a 470...

But I still got 15 v on the meter

Tried a 1,000 ohm...still 15 volts.

I've used these meters for decades, never saw
this situation...checked the meter against
other known voltages...worked OK.

So I opened the over 40 year old Varney Mark III
power pack and found the variable resistor used
as the speed (voltage) control was damaged...
even so, it was putting out 15 v dc.

Anybody got any ideas about this unusual kettle 
of fish?

And how could that damaged variable resistor, in effect,
null the resistors I was using?

Don


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## NIMT (Jan 6, 2011)

A long electrial explanation would be needed to answer you compleately!
Simple answer the resistor will not dorp any voltage if there is no load.
Check the drop with a load on it.


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## gunrunnerjohn (Nov 10, 2010)

Ohms law.  Your meter didn't provide the load as Sean says, so it was for all intent, invisible.


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## DonR (Oct 18, 2012)

Sean

Thank Yew...it works when done right.

I abandoned the Varney and got a wall wart that 
claims to put out 9 vdc...with the resistors and
the LEDs soldered in...7.50 vdc...and the LEDs
are just the right brightness for building lighting.

They're self adhesive...so will be a snap to install...
hard part...blacking out the see thru plastic walls...

Don


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