Powerdynamo, voltage output of PD regulator

Powerdynamo brings new ignition & light
to your vintage motorcycle



Technical Help



Checking voltage output of Powerdynamo DC regulator

we are sometimes confronted by customers with such statements as
  • my battery is not getting charged as your regulator delivers not enough
  • your regulator burns my light bulbs
  • your regulator makes my battery boil

In this context we are asked what the charge current is our regulator delivers to the battery. Now, all our regulator are tension regulator and not current regulating (as most classical regulator). In other words, they try to keep voltage at the norm level, irrespective of current (in ampere) flowing.

You will  remember Ohms law from your school days.

As the regulator keeps its voltage (V) about stable, the current (I) depends in the resistance (R) - in  this case of the battery. Is this resistance too low, in some cases of plate shorting near zero, current rises. At times so significantly that the magneto can not keep the voltage supply to the regulator which in turn can not keep voltage. After all P=U*I (power is voltage * current) and the  power produced by the magneto is limited.

Unfortunately there are very many (cheap) batteries on the market which are bad from start and have a very low resistance as plates ans shielding betwen them has been kept to a bare minimum.

Also, a battery has only a limited lifespan (and needs care which it more often than not does not get). The result very often are sulphated plates which can no longer convert the energy offered by the generator into chemical energy, but just change it to heat, therby drawing a lot of current. See our info here.

If you find that your lighting voltage suddenly is too low, it is well worth for a test to disconnect the battery (suspected to burn a lot of it) and test lighting without. Sure you will have to rev the engine a bit, at idling it will not be enough.

Now, the battery is not the only element in a bike´s electrical system. There are numerous consumers, notably the headlight, flasher bulbs, stoplight etc. Please know that even as our name is Powerdynamo, the systems we sell are for small, older motorcycles and do not produce endless lighting energy.
You may see the output diagrams and some explanation here.

Also it can be that you do not use a battery at all, which most of our systems permit. See however our info on this

If the 9522 is used without battery than there are certain issues to observe as the frequency of the produced voltage changes considerably with engine speed and may produce ceratin negative effects:
# side indicators may not work properly
# horn may sound strange or even not work at all
# bulbs may blow if light is switched on with engine already reving

Those effects may be cured by installing a smooting capacitor. BUT, (without battery and with this condenser)  there is not a small consumer of at least 2 watts present (e.g. indicator lamp) voltage of the regulator may rise over 20V, possibly up to 50V, but go back to normal 14.4 when a consumer (a light) is switched on.

Regulator 7300 has none of those negative effects, but this regulator does not have a terminal for a charge control  light considered by many as essential.

All the above mentioned has to be taken into consideration when you read the below table of average voltage values.

no regulator
no load
AC output 
of stator
regulator 7300 
output in volt,
no load
regulator 7300
output in volt,
50W load
regulator 9522
output in volt,
50w load
no battery
regulator 9522
output in volt,
50w load
no battery
with condenser
regulator 9522
output in volt,
50w load
with battery 12v
V_bat = 14.4
with 50W = 11.9V
500 6.3 7.4 3.2 2.2 2.2 11.8
1000 10.2 13.9 6.4 5.9 5.9 11.8
1500 15.1 13.9 10.8 9.3 9.3 12.0
2000 19.8 13.9 13.6 11.8 12.6 12.4
2500 25.7 13.9 13.8 10.3* 14.4 13.0
3000 30.8 13.9 13.8 8.5* 14.4 13.4
3500 36.9 13.9 13.8 8.2* 14.4 14.1
4000 40.1 13.9 13.8 7.4* 14.4 14.3
4500 46.8 13.9 13.8 7.1* 14.4 14.3
5000 50.3 13.9 13.8 6.4* 14.4 14.3
5500 55.8 13.9 13.8 6.2* 14.4 14.3
6000 61.9 13.9 13.8 6.0* 14.4 14.3

For the strange voltage readings marked here with an asterix (*) see explanation here

Please see also our other battery / regulator related entries
For taillights or rear flasher keeping burning consider vibration as a reason. 
try to fit them differently and/or afix some small mass (some larger screw or so) nearby to shift vibration there
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