If there's no voltage there and the batteries are connected
that sounds like a short circuit (~0 volts).
I’m unsure if it needs to be connected to the battery before it will output the correct voltage.
Nicad chargers are generally pretty simple things. Examining photos of it, I see that there needs to be a single voltage selection screw in the correct spot, but otherwise, you should be seeing a lot more than 0.4 volts under no-load conditions.
That's apparently not the case.
0V is quite not the same as a short circuit and indeed, a charger outputting 0V (or rather, close to zero but not quite) is in all likelihood not shorted at the output.
Leonhard Stiny, Grundwissen Elektrotechnik und Elektronik. Eine leicht verständliche Einführung, 7. Aufl. 2018, Springer VerlagIf a voltage source is short-circuited (e.g., with a thick wire), its terminal voltage is 0 volts. The total source voltage drops across the internal resistance
If there's no voltage there and the batteries are connected, that sounds like a short circuit (~0 volts).
I'm assuming that the charger delivers the 14.4 volts
Therefore, the charger's open circuit voltage should be measured to determine where the fault lies.
Yeah, so that's the assumption that we're checking here and which seems to be not the case. He asks if it's normal if his charger actually doesn't output 14.4V, but instead outputs 0.4V without batteries connected to the output. I.e. the open loop voltage is close to zero. This doesn't imply a short circuit. A short circuit can be involved somewhere, but there's no evidence for it presently.
That's what he did! Read post #1!
but I wanted to ask anyone with this charger if they read the correct voltage without out the charger connected to the battery
So, if anyone has this charger and you have a meter, I would be grateful if you could plug it in and measure the voltage on the two pins. View attachment 399065
Wowza, that's a half-watt charger. Trickling with a vengeance. That's a very dumb charger, designed to be disconnected after 6 hours, but not damage the cells if you do leave it connected. OP, has it worked in the past? Has it worked recently? Or is it new to you? I'd probably remove and reinsert the voltage selection screw just to make sure there's no corrosion on that side of things. There is a "built-in safety device" (i.e., fuse) which can be replaced by a service center, so I'd probably have a peep inside to check the fuse which is almost certainly OK, then check the voltage before it gets to the charger cord.
Equivalent circuit
View attachment 399022
The 14.4 volts remain at the voltage source. At its output, you measure close to 0 volts due to the short.
- Voltage source: 14.4 Volts DC
- Load: 0 ohms (short)
- Internal resistance of the voltage source: 2 ohms (or higher/lower)
- Load (resistance of the copper cable/0.5 mm, 10 cm length): 8,55 milliohms
- Voltage drop on the line: 61.4 mV
As an example, I just pulled a transformer-type DC adapter out of my box of such junk (used once upon a time to charge an old bicycle light, before Li-ion batteries). It's rated 9 VDC and 300 mA output. Connecting a DVM across it with no load, it reads 10.7 VDC. This is not as extreme as your example, but this one has a higher output current rating so it would get pulled down less.
What could be causing my charger to have double the output voltage?
The fact that your charger's output current rating is so low means it has a high internal resistance and connecting a load will pull its voltage down.
Regarding your copy of the charger, I think these types of dumb chargers for NiCd and the like usually have a fairly high no-load voltage and drop closer to the rated voltage when the load is connected - meaning, the internal resistance of the charger source is comparable to the internal resistance of the battery. The fact that your charger's output current rating is so low means it has a high internal resistance and connecting a load will pull its voltage down.
What could be causing my charger to have double the output voltage? I suspect it's a transformer, a rectifier, electrolytic capacitors, and a voltage regulator.
I'm not sure there is a voltage regulator in a transformer based dc adapter of this vintage.
**Current matching** in power supplies refers to ensuring that the power supply can provide at least as much current (amperage) as the connected device requires. The output current rating of the power supply must match or exceed the device's needs—using a supply with a higher current rating is safe, but the voltage must match exactly[4][8].
In practice, "current matching" is less about adjusting the supply to a precise current and more about selecting a supply that meets or exceeds the device's current demand. The device will only draw the current it needs, provided the supply can deliver it[4][8].
If a power supply offers current limit adjustment, it can be set to restrict the maximum output current to protect the device, but this is typically called "current limit adjustment" or "current setting," not "current matching"[3][4].
Quellen
[1] Power Supply Basics: Function and Operation Explained https://www.actpower.com/blog/what-is-a-power-supply-and-how-does-it-work/
[2] POWER SUPPLY BASICS - Wavelength Electronics https://www.teamwavelength.com/power-supply-basics/
[3] Glossary of Power Supply Terms - Bel Fuse https://www.belfuse.com/resource-library/tech-paper/glossary-of-power-supply-terms
[4] Can I Use a Charger With the Same Voltage but Different Amperage ... https://askleo.com/same-voltage-but-different-amperage/
[5] How to Choose a Power Supply? AC to DC Power Supply Introduction https://www.fsp-group.com/en/knowledge-tec-26.html
[6] Power supply - Wikipedia https://en.wikipedia.org/wiki/Power_supply
[7] Understanding DC Power Supplies – ITP Physical Computing - NYU https://itp.nyu.edu/physcomp/lessons/electronics/understanding-dc-power-supplies/
[8] Choosing power supply, how to get the voltage and current ratings? https://electronics.stackexchange.c...ly-how-to-get-the-voltage-and-current-ratings
A case for Perplexity
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