Measuring battery charging voltage

Charging voltage will change on a battery. The load changes as the battery charges. The circuitry of the charger controls over charging of the battery. In doing so will not use the full output being generated.

It would not be a good test if taken on the battery if you looking to record output to wind speed of the generator I would use a fixed load.

Hi Anthony:

The terminal voltage of the battery IS the charging voltage, but it is determined by the characteristics of both the battery and the charger. Those characteristics will be different in an open circuit condition than when they're connected as a system.

They can each be characterized more completely by a series of controlled voltage and current measurements, but that can be quite complex as the state of battery charge varies, particularly if the charger has control features to protect the battery.

Analysis of a series of speed, voltage and current measurements from the operating system may help you develop an adequate "feel" for its capability.

Best regards.

DickL

You say it is 3 phase, assuming that the propeller blades are not of a varying type for different wind speeds, you could measure the frequency to get an indication of wind speed.

Using a fixed resistive load (to remove the variable of the battery/charger), you could measure both voltage and current and plot them on a PC screen together with the frequency with some software package or MS Excel for example.....

With regards to the battery, the state of the charge of the battery will vary the voltage measured.......as current drops as the battery gets more and more charged, the voltage will rise.......assuming a Lead Acid battery.....a little bit more complicated, especially if the battery is also being discharged with usage...

Guys thanks for your help on this.

It sounds like I need to replace the batteries with a load resistor to have a valid test.

The system is 24V and rated at 400W the current varies from 0 to 20A max.

So if I had a 500W, 1ohm resistor connected to the charge controller I should be able to measure the o/p voltage and current.

The wind speed should not be a problem as I have an annemometer and datalogger.

Can you confirm that this is correct and the load resistor should be sufficient.

Thanks again

Anthony

That is a resistor with at least 400 watt rating, you may have a job finding one easily and it will probably need to be oil cooled.......

ever thought about a diode between the battery and test point.

Can you elaborate on this a little.

Is the idea of the diode to stop current flowing from the batteries?

Will this enable me to measure the voltage being o/p to the batteries.

If there is no load connected to the batteries why would there be current flowing?

Thanks

Anthony

this is only a theory but with a diode between the test point and the batteries you should only read the voltage from your source of power transmission.yes stopping flow from your batteries could be done with a diode.Interesting problem let me know how it works out .you would have take your load downline of the diode.hope this helps.

I assume that Physics was not your favorite subject from your last two posts........

Check the controller to see if it has charging voltage monitor. I won't put a resistor on it to test.

From your description, the controller is a constant voltage charger for 24V battery. It'll maintain 24V charging voltage and change charging current according to battery capacity. So in that case you won't see any different in charging voltage. You'll need to check current to see the different.

Connecting a resistor to the charger will result in the charger seeing no voltage (ie high voltage drop) and charger will increase both voltage and current to charge the resistor. You'll destroy the resistor if you're lucky. If you're not, the controller will be smoking.

Connect a flat (output less then 24V) battery to test.

Thanks for your input

The controller monitors the battery voltage and stops charging when it reaches 29V.

Manufacturers data show o/p voltage between 24.6V and 27V so there is a bit of variation. To keep it simple it I could take the voltage to be 26V and just monitor the current.

I would prefer to leave the battery connected but know that when reaches 29V then controller will stop charging.

I can run a couple of lights of it to try and keep below the 29V just leaves it a bit more complicated.

Let me know what you think

Thanks

Anthony

There are resistors made for some of the old style speed controller for Electric Vehicles. One of them should handle the 400w load. Look for Norskog, Club Car, Taylor Dunn or E-Z-Go for the resistor.