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#1359910 - 10/28/18 06:12 PM

Dynamo Voltage (possible) Hazard

ConRAD
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Originally Posted By: "ConRAD"

When I was young I remember that I often used to adjust with the right hand the sidewall dynamo connection-wire sometimes accidentally coming loose while cycling.
Making sure to secure at the same time with the left hand the handlebar on a not very well insulated grip I remember also that some perceptible and quite annoying
leakage current was indeed crossing my body.

Well, IEC-International Electrotechnical Commission states that for voltages around 50V human body on a hand-to-hand pattern has an impedance
of about 1500 Ohm or even less, that one significantly depending on actual body mass, skin conditions, contact area, applied voltage, frequency, etc.
Now the point: at 50 km/h at no-load conditions, or on a 1500 Ohm load with no significant difference at all, out of a dynamo without a built-in voltage protection
you may have something like 50V that applied to your body might induce in turn something like 30 mA.
Something definitely unlikely to happen, I agree, but still possible … especially for grounded hub dynamos and spoilt head lamps with exposed/not well protected live parts.
From the point of view of a possible exposure hazard IEC worked out the below Current-vs-Time plot identifying four zones:

Zone 1: represents the limit for current perception estimated to be 0.5 mA

Zone 2: represents the danger threshold generally recognized still to have no dangerous physiological effects

Zone 3: it’s a sort of an “alert” area coming just before any possible atrial fibrillation, mainly characterized by yet reversible physiological effects
such as muscular contraction (tetanization), difficult respiration and cardiac disturbances. As you can see 30 mA for one sec may already have some annoying effect.

Zone 4:is characterized by permanent effects, such as fibrillation, depending, beyond current and time, also on specific health conditions.
Contact times as low as 10 ms may be lethal but fortunately these current values seem to be much higher than those ones actually supplied by a dynamo at 50 km/h !!

Prendendo il largo
Bike in the night
oKKio al Watt

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#1359964 - 10/28/18 09:03 PM

Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]

derSammy
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Hi ConRAD,

I'm not sure, if your assumptions apply. A bike dynamo is a constant current source, with a current of about 500mA.
You are right, unloaded the voltage can be extremely high, I remember something like ~1V per km/h? But the voltage drops significantly with the presence of a load. To the best of my knowledge it is almost impossible to get more than 10W from a bike dynamo. Are these circumstances suficient to get a significant hazzard for the human body?

Moreover I want to point out two aspects:
(1) The danger to harm your fingers or even to do a front spin with the bike seems to be much more likely than electrical issues, when you perform ajustments like you descriped.
(2) When you cycle faster than -let's say 20 km/h- it is a realy good idea to keep both hands at the bars. People doing dynamo adjustments at 50km/h apply for the Darwin Award. Not because of electrical issues, but because of general safety rules.

And, last but not least, I highly recommend the use of a dynamo hub, which avoids a lot of the drawbacks of the old-fashioned bike dynamos.

Komm wir grillen Opa. Es gibt Koch und Suppenfleisch!
Satzzeichen können Leben retten.

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#1360013 - 10/29/18 08:25 AM

Re: Dynamo Voltage (possible) Hazard [Re: derSammy]

ConRAD
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Hi derSammy, thanks for your reply.
Yes I agree with you, at 50 km/h is definitely much better to keep both the hands on the handlebar !!
Here below nevertheless some of my points:
A bike dynamo is a constant current source till the load is a prevalent resistive load and its value is negligible compared to the internal reactance of the dynamo; 500-600 mA is the maximum output you can get from a dynamo, even at 100 km/h on a dead short-circuit load !!
Yes I confirm: no-load voltage is something like ~1V per km/h.
A 6V-3W hub dynamo is capable of delivering 6W at 20 km/h, 10 W at 50 km/h.
Output voltage of a dynamo of course is likely to drop with load but the typical 1500 Ohm of a human body will not affect substantially this value at all.
... sometimes just a few mA can kill and that's why worldwide households electrical protection, at least against "indirect contacts", has been generally specified to be put in place through the installation of a good grounding system in combination with a 30 mA RCD-Residual Current Device.
The IEC

plot below shows that 100 mA for 1 sec might be lethal.
Cheers

Prendendo il largo
Bike in the night
oKKio al Watt

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#1360263 - 10/29/18 08:26 PM

Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]

derSammy
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I don't know where the diagram is from and I need to admit, that I did not think about the deadly hazzard limits of electricity yet.
But I nowhere found an indication, wheather the values hold for DC or also AC (and what is more dangereous)?

However, 1s seems to be quite long in my perspective. 54km/h is 20m/s or about 10 roations of the wheel per second. In other words the current will have changed direction about 130 times in 1s.

Komm wir grillen Opa. Es gibt Koch und Suppenfleisch!
Satzzeichen können Leben retten.

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#1360362 - 10/30/18 08:15 AM

Re: Dynamo Voltage (possible) Hazard [Re: derSammy]

ConRAD
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The above diagrams are based on IEC electrical safety related standards and in my case more specifically on publications of Prof. V.Carrescia teaching “Electrical Safety” at the Polytechnic of Turin, Italy.
Considering the very low currents involved I don't think there are big differences between DC and AC, except for body resistances/impedances varying according to specific frequency.
However here below some actual measurable numbers:

50 km/h is 13.9 m/s (50000m/3600s)
13.9 m/s is approx 6.3 rps (rotations per second based on a 28” wheel)
6.3 rps is approx 82 Hz based on a 26-poles hub dynamo

Prendendo il largo
Bike in the night
oKKio al Watt

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#1360374 - 10/30/18 08:44 AM

Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]

derSammy
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Your calculation is correct, 54/3,6=15, not 20 as I claimed. And I probably mixed up the number of magnets and the number of poles.

Komm wir grillen Opa. Es gibt Koch und Suppenfleisch!
Satzzeichen können Leben retten.

Edited by derSammy (10/30/18 08:44 AM)

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#1403724 - 10/23/19 09:50 AM Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]
kangaroo Member Offline Posts: 1,373	i dont know whats the point. You cant have the Current and the Voltage so high that its getting dangerous. You can maybe reach one but not both. 50VAC or 120VDC
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#1415209 - 02/10/20 10:57 AM

Re: Dynamo Voltage (possible) Hazard [Re: kangaroo]

ConRAD
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Originally Posted By: kangaroo

... you cant have the Current and the Voltage so high that its getting dangerous. You can maybe reach one but not both ...

Well, according to IEC-International Eletrotechnical Commission, 30 mA should be regarded as a sort of an "alert borderline", AC or Dc it doesn' matter.
At 50 km/h in case of an accidental contact with live parts, considering a body impedance of approx 1500 Ohm, you might be interested by a direct contact with 50 V exposed parts sufficient to produce in turn a current of 30 mA, or even more.

Prendendo il largo
Bike in the night
oKKio al Watt

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#1431864 - 05/14/20 09:43 AM Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]
kangaroo Member Offline Posts: 1,373	half right half wrong 30mA ist the Current, where it doesnt matter if AC or DC But for the Voltage side the limits are as i wrote above and you will not have 50V if you have a body connected, the voltage will imidialy drop. This dynamos just produce 50V with nothing connected. Importend for the harmfullnes is also the time the body is exposed to it.
	Edited by kangaroo (05/14/20 09:47 AM)
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#1431926 - 05/14/20 10:21 PM Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]
AndreMQ Unregistered	As far as I know: A bike dynamo has by nature a significant internal inductance. In case of any external load (including human body) this leads with increasing speed and frequency also to an increasing voltage drop in the dynamo. This limits the terminal voltage and the current although bike speed an internal EMF increase. For decades this feature allows to operate classical 6V-bulbs without any control electronics and brings also intrinsic safety. State-of-the art LED-light-electronics are designed to be supplied with this limited power, variable frequency AC-source. For systems like Forumslader this is not sufficient. Therefore at first Forumslader has to compensate the internal inductance with an external capacitor (for a certain frequency/speed range) followed by the rectifier diodes.
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#1432167 - 05/16/20 05:19 PM

Re: Dynamo Voltage (possible) Hazard [Re: ]

ConRAD
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"Classical" filament lights are 6V/2.4W/50 Ohm and 6V/0.6W/15 Ohm (front and rear light respectfully). When connected in parallel they account as an equivalent 12 Ohm resistor.
As a 12 Ohm resistor they draw 500 mA approx and that why the voltage drops to a nominal value of 6V (at 20 km/h).
Human body has a much higher impedance and the voltage will not drop at all!!!

Prendendo il largo
Bike in the night
oKKio al Watt

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#1432180 - 05/16/20 07:17 PM Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]
AndreMQ Unregistered	Let us assume that the internal voltage drop is not relevant any more then we see 46,2Vrms/1500ohm = 31mArms which is not a safety problem. Normal RCCB (Fehlerstromschutzschalter) are rated for 30mArms. This means: There is no dynamo voltage hazard same as with older ignition systems for gasoline cars which produce around 10.000V but with very high internal resistance so that no significant current flow can occur. Modern ignition system are more powerful but still are only dangerous for people with cardiac pacemaker. There must be a current flow and especially during vulnerable period of the heart. Outside this period even lightning flashes can be survived.
	Edited by AndreMQ (05/16/20 07:27 PM)
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#1432687 - 05/20/20 07:49 PM

Re: Dynamo Voltage (possible) Hazard [Re: ]

ConRAD
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Originally Posted By: AndreMQ

... normal RCCB (Fehlerstromschutzschalter) are rated for 30mArms...

... yes that's true, but 30mArms are to be regarded as a sort of an "alert borderline" ... and NOT as a "trustable no-exitation safetyline"

IEC-International Electrotechnical Commission states that for voltages around 50V human body on a hand-to-hand pattern has an impedance of about 1500 Ohm or even less, that one significantly depending on actual body mass, skin conditions, contact area, applied voltage, frequency, etc.
Now the point: at 50 km/h at no-load conditions, or on a 1500 Ohm load with no significant difference at all, out of a dynamo without a built-in voltage protection you may have something like 50V that applied to your body might induce in turn something like 30 mA. Something definitely unlikely to happen, I agree, but still possible … especially for grounded hub dynamos and spoilt head lamps with exposed/not well protected live parts.
From the point of view of a possible exposure hazard IEC worked out the below Current-vs-Time plot identifying four zones:

Zone 1: represents the limit for current perception estimated to be 0.5 mA

Zone 2: represents the danger threshold generally recognized still to have no dangerous physiological effects

Zone 3: it’s a sort of an “alert” area coming just before any possible atrial fibrillation, mainly characterized by yet reversible physiological effects such as muscular contraction (tetanization), difficult respiration and cardiac disturbances. As you can see 30 mA for one sec may already have some annoying effect.

Zone 4:is characterized by permanent effects, such as fibrillation, depending, beyond current and time, also on specific health conditions. Contact times as low as 10 ms may be lethal but fortunately these current values seem to be much higher than those ones actually supplied by a dynamo at 50 km/h !!

Prendendo il largo
Bike in the night
oKKio al Watt

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#1432698 - 05/21/20 05:33 AM Re: Dynamo Voltage (possible) Hazard [Re: ConRAD]
AndreMQ Unregistered	Originally Posted By: ConRAD ... yes that's true, but 30mArms are to be regarded as a sort of an "alert borderline" ... and NOT as a "trustable no-exitation safetyline"[/b]... This IEC-diagram is only a little part of the electrical safety issue and cannot be taken out alone. The hugh amount of data for this issue is based on animal tests and on recalculation of fatal accidents and started around 100 years ago. At first all these values are based on probability calculations, furthermore there are attentuation factors for the current path relativ to the standard left hand - left foot. The body resistance is between 500 and 1300ohm but the skin resistance can be around 10kohm - especially for low voltage applications. Therefore IEC defines "extra low voltage" below 50V (ACrms) and below 120V (DC). This is regarded as safe and non-lethal for permanent touch by normal adults. A bicycle dynamo cannot exceed around 3 - 5W if operated with resistive load (intended use) due to the (high) internal inductance. This can be easily calculted with a AC-circuit ("komplexe Wechselstromrechnung"). Forumslader is not an intended use of a bicycle dynamo because it compensates this internal inductance by an external non-resistive load (a capacitor). But still the voltage limit 50V (ACrms) is normally kept and there is no safety issue. If you plug this dynamo with two needles around the heart area like a cardiac pacemaker then you will have an effect. I would not recommend to do this.
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