ac voltage before rectified

[jmk]

 Now that I am getting my SW 24/40 inverter figured out I can have it display battery bank voltage on the display. Being so, I decided to switch my multi meter to ac and put it on two of the phase legs at the rectifiers. I am using three 35 amp bridge rectifiers. I know the battery bank is supposed to hold the voltage down to battery voltage. Shouldn't this be about 7 volts per phase, 14 volts two phases, and 21 volts three phases to reach cut at a 24 volt dc battery bank? I have on two legs  hitting about 25-26 volts ac when I can see the amp gage start to move, and with amps coming in like 10 or so it holds strong at 27 volts. This what my battery reads in dc, 27.2. Shouldn't it hold strong at about 14-15?      

[jmk]

 Now watching it hit 20 amps it goes to 30 volts.

[Flux]

At cut in the ac volts across a pair of ac leads of the rectifier will be about 17V to reach 24v dc. With the battery above 24v and with diode drop then likely 20v at cut in.

At cut in the dc current will be very small, in the mA region.

Once the diodes are well into conduction the ac volts are chopped to a square wave with the peaks clamped to the + and - dc rails.

What an ac meter will read depends on the severity of the clipping and on the type of meter. A true rms meter will read very differently from one calibrated mean and scaled rms.

The real truth is that it is totally meaningless and best avoided.

Measuring ac is only useful without the rectifier to decide your cut in speed.

With no rectifier connected, a star circuit will have phase volts from any line to neutral. The line volts between a pair of output leads will be 1.7 x phase volts.

These relationships will hold with resistive load ( within waveform error limitations) but when you connect a rectifier just forget ac volts.

Flux

[jmk]

 My turbine is out of view from the battery bank and I thought it would be nice to see how close it is to cut in by the ac side. Then It alarmed me to the thought of what its doing. I just wanted to make sure I have it hooked up right, and it,s doing what it is suposed to. I was just thinking that it wasn't suposed to get that high, and seeing that is I thought something might be wrong. Thanks for the reply. I do notice the inverters reading in dc is a couple volts lower than the dc on the multi meter. I tend to beleave the inverter on the basis of the saying ( You get what you pay for.) thery.