I've just plugged in my wife's bike to charge and got a small shock from her pannier rack, got the meter out and I'm getting up to 2v coming though the rack near the battery when charging!? The battery is a metal case, I'm guessing the charge leads have managed to ground to the case. Could this become dangerous over time?
Strange potentially dangerous grounding issue
- Thread starter anon4
- Start date
Some chargers are not fitted with an earth connection and seem to leak a small amount 220v into the output. I think this is caused by 'stray' or parasitic capacitance in the charger. I have also come across this with cheap replacement laptop chargers.
https://en.wikipedia.org/wiki/Parasitic_capacitance
PS Modern chargers switch at high speeds and generate high frequency voltages that can get through small stray capacitance e.g. between the motor coils and the hub frame etc.
https://en.wikipedia.org/wiki/Parasitic_capacitance
PS Modern chargers switch at high speeds and generate high frequency voltages that can get through small stray capacitance e.g. between the motor coils and the hub frame etc.
Last edited:
Two or three wire mains lead?
Plastic or metal charger case?
If metal, is the mains ground wire connected to the case?
Did you measure using AC or DC scale/setting on the voltmeter, the 2 volts to the rack?
I see this mainly on things like Satellite receivers? But that is not saying that its right.
Is the positive or the negative side of the bike battery,connected to the bike frame internally?
it could be possible that the socket you are using is not correctly wired into the mains supply.
Are you yourself an electrician?
You might want to add an extra ELCB/RCD to the circuit for the bike. See here:-
Residual-current device - Wikipedia
en.wikipedia.org
Earth-leakage circuit breaker - Wikipedia
en.wikipedia.org
I personally would not live in a house without one...
I can tell you from personal experience, that getting a shock even with a fully working and tested RCD in circuit is still painful, but not life threatening.
Andy
It is quite common for switched mode power supplies to have a small capacitor between the live input and the low voltage output. This is done to reduce electrical interference and is allowed by the approval authorities. There is a small ac current back to the low voltage side but too low to affect an earth leakage trip or be dangerous. If you measure the voltage to earth with on AC volts range you will probably see 110 v.
Having said that we never used that technique on our PSUs
Having said that we never used that technique on our PSUs
We have a circuit breaker, saying that it could be the socket, I have the chargers on one of those double plugs, could that be the problem? The charger case is plastic, pretty sure I measured using the DC setting. The battery case is metal and does have direct contact with metal parts of the frame, I don't believe there are any shorts happening that shouldn't be, everything appears correct on the battery and bike. The charger has 3 pins, inside the battery only 2 are wired up, is that right? Or should the third be used for an earth? I'm no electrician but can fix things with instructionsTwo or three wire mains lead?
Plastic or metal charger case?
If metal, is the mains ground wire connected to the case?
Did you measure using AC or DC scale/setting on the voltmeter, the 2 volts to the rack?
I see this mainly on things like Satellite receivers? But that is not saying that its right.
Is the positive or the negative side of the bike battery,connected to the bike frame internally?
it could be possible that the socket you are using is not correctly wired into the mains supply.
Are you yourself an electrician?
You might want to add an extra ELCB/RCD to the circuit for the bike. See here:-
These are older style ones, better than noting!:-Residual-current device - Wikipedia
Especially if your house mains does not have one installed.Earth-leakage circuit breaker - Wikipedia
I personally would not live in a house without one...
I can tell you from personal experience, that getting a shock even with a fully working and tested RCD in circuit is still painful, but not life threatening.
Andy
Exactly what type of circuit breaker? They all look much the same, but there are important differences. Please identify it exactly. A normal type of circuit breaker has no safety for living things....
Everyone should have one per phase, so as most household mains is a single phase in the UK, there should be one as the main breaker. The trouble with that is that a single failure and the hose is all off!
If each circuit has one, then that does not happen...but costs are higher, but a dead family member.......Is something else!
Did you measure the leaking voltage using an AC setting? I would guess that its a lot higher than 2 volts, as few people will even feel 30 volts or less....
Provide the circuit is on an RCD or similar, the level of danger is reduced dramatically....
Maybe a good idea is to earth the bike frame while charging, then there should be no more sensing of a voltage.
I suspect that the problem lies with the charger insternal design, and should be within allowed limits, but earthing the frame and adding an RCD will simply make its safer.
regards
Andy
D
Deleted member 25121
Guest
If you touch the metal case of an appliance that's not using the mains earth connection you will often get a static like tingle, it's down stray capacitance inside the power supply. There's miniscule current available so there's no danger to yourself.
Your DVM will have a very high input impedance and will only draw a miniscule current, the 2V it indicates is of no consequence.
Your DVM will have a very high input impedance and will only draw a miniscule current, the 2V it indicates is of no consequence.
I agree with that completely, but I still recommend an RCD as well.
It depends on whether he was measuring on AC or DC.
Remember, 2 volts will not be felt by anyone, unless you are using their tongue or something else very sensitive!! Not fingers....
It should be measured using the AC voltage range. That might tell a very different story, a voltage high enough that a human might actually feel. say 50 VAC or higher.
Have a great day.
Andy
D
Deleted member 25121
Guest
2V is being measured against the input impedance of the DVM. The input impedance of a human could be higher in which case the perceived voltage will be higher. It's basically ohm's law.
I have actually seen this phenomena many times on different equipment, and I have measured with a DVM on an AC range each time, always for safety reasons, and when I have "felt it", it has always been over 100 VAC.
Naturally, an older or even a defective meter with a very low impedance might measure a lower voltage that a good high impedance DVM will, it is as you say only Ohm's Law.
But generally speaking a good modern DVM will have a much higher "Ohms per volt" and will therefore actually be far higher resistance than an average human.
So the human being having a lower resistance, will actually drop the voltage far more, than a halfway decent meter....
Only a really old, low "Ohms per volt" meter will be around a human's body resistance.
I measured myself on a digital meter, and I got a value of under 6 Meg Ohms (dry skin), between my left and right hands....
The meter I used (a mid price range DVM), has 10 meg ohms per volt!
Some more expensive DVMs can go up to 1 Gig Ohm per volt! See here:-
Voltmeter - Wikipedia
en.wikipedia.org
For instance on the 200 volts range of an average DVM, we are talking about 10,000,000 x 200 = 1,000,000,000 Ohms!!
I actually believe, as I mentioned before, that the apparent error might simply be that the OP measured using a DC range (or a DC only Meter) on the meter, but guessing only!
Maybe he will let us know!
Andy
PS. A younger person than I, would also usually have an even lower skin resistance than I do....My skin is very dry!
D
Deleted member 25121
Guest
Rest your fingers on your DVM probes and I doubt it will even register a resistance, the contact resistance is much higher than the resistance through your body. Try it. When you feel a tingle caused by stray capacitance in a power supply it's when you brush against the case, not when you grab hold of it (in which situation the body resistance and hence voltage will be much lower).I have actually seen this phenomena many times on different equipment, and I have measured with a DVM on an AC range each time, always for safety reasons, and when I have "felt it", it has always been over 100 VAC.
Naturally, an older or even a defective meter with a very low impedance might measure a lower voltage that a good high impedance DVM will, it is as you say only Ohm's Law.
But generally speaking a good modern DVM will have a much higher "Ohms per volt" and will therefore actually be far higher resistance than an average human.
So the human being having a lower resistance, will actually drop the voltage far more, than a halfway decent meter....
Only a really old, low "Ohms per volt" meter will be around a human's body resistance.
I measured myself on a digital meter, and I got a value of under 6 Meg Ohms (dry skin), between my left and right hands....
The meter I used (a mid price range DVM), has 10 meg ohms per volt!
Some more expensive DVMs can go up to 1 Gig Ohm per volt! See here:-
The higher the input resistance, the higher the voltage measured (Ohm's Law as you mentioned), due to the meter NOT loading up the voltage as much.Voltmeter - Wikipedia
For instance on the 200 volts range of an average DVM, we are talking about 10,000,000 x 200 = 1,000,000,000 Ohms!!
I actually believe, as I mentioned before, that the apparent error might simply be that the OP measured using a DC range (or a DC only Meter) on the meter, but guessing only!
Maybe he will let us know!
Andy
PS. A younger person than I, would also usually have an even lower skin resistance than I do....My skin is very dry!
Did you realise that the voltage on a statically charged balloon can easily be over 1,000V?
By the way, the input impedance of a voltmeter is measured in ohms, not ohms per volt. Ohms per volt is a measure of the sensitivity of the instrument, a totally different parameter. Typical input impedance of a modern DVM is in the 10-100Mohm range.
It's a crabtree starbreaker, no idea what kind it is. Reassuring to know that this is a normal phenomenon, as someone mentioned it is more like static as it's felt when brushing rather than holding. How would I go about earthing the bike frame?
You do need to hold the probes as only light touching will give a very variable reading, hence resistance. The human body is variable enough in resistance, from person to person from day to day, from sweating to not sweating!
Furthermore, I have noticed over a great many years, on many 2 wire mains devices, particularly those that are grounded in service, for instance SAT receivers, that when the coax cables are not connected, the frame floats and there is a high resistance mains signal on the case, if metal, and on the antenna connection earths.
Very easily seen on a scope or a DVM...or felt!
As I worked for many years for several large American computer companies, and part of my job was to eradicate static on such things as very large printers (some jokingly called them "van der Graaf machines" in fun!), I am sure that I actually know a lot about static! See:-
Van de Graaff generator - Wikipedia
en.wikipedia.org
I was often working on equipment, that if not set up correctly, could produce thick blue sparks 2 inches long, every 10 seconds or so! They could even cause the main computer to error, as well as stopping the printer in its tracks! I had to manage that the buildup of the charge did not happen at all! Not difficult really!
Meters are ALWAYS quoted in Ohms Per Volt sensitivity, simply because changing the range changes the internal circuitry and the actual resistance across the probes. This changes the accuracy of the reading shown. Many forget it nowadays as the internal resistances have got so high, but one should not completely forget it!!
Read this, link is underneath!!:-
Ohms Per Volt
Sensitivity rating for measuring instruments, obtained by dividing the resistance of the instrument in ohms at a particular range by the full-scale voltage value at that range.
See here:-
ohms per volt
Encyclopedia article about ohms per volt by The Free Dictionary
encyclopedia2.thefreedictionary.com
I hope that this helps you further.
Andy
D
Deleted member 25121
Guest
Yes, that's the phenomenon I'm referring to and the one that the OP is seeing.
The OP has nothing to be concerned about.
D
Deleted member 25121
Guest
Related Articles
-
MTF Enterprises announces acquisition of EMU Electric Bikes- Started by: Pedelecs
-
Wisper 806T folding bike wins Which? ‘Best Buy’- Started by: Pedelecs
-
Sustrans calls for protected cycle lanes- Started by: Pedelecs
-
Amazon launch their first UK e-cargo micromobility hub- Started by: Pedelecs
