I have a power supply which is computer controlled to charge car batteries. it connects to the battery via induction sensors. I am trying to build a meter for its out put to see what the output voltage is at the charging battey. Problem im havin is that the induced output power induced into a charging coil, keeps jumping around and is not a steady voltage.
I was thinking of a sample and hold circuit but the AC output voltage at the coil is maybe 0.4 volts peek.
I even tried to just put a capacitor at the output, but all that does is slow down the jumping around.
How can i put a leash on this thing? Any ideas would be appreaciated.

 

AC output voltage at the coil is maybe 0.4 volts peek.

You are not charging any car batteries at that voltage.

Can you post some pictures of this charger and the inductive coils? What you have described us entirely unfamiliar to me.

 

First question: What sort of "car batteries" are being charged??? My guess is not those 50 KWH and larger high voltage electric vehicle batteries, but possibly smaller ones. So just what sort of charging system are you attempting to measure?? And what sort of pickup coil are you using?

First, induction charging of batteries is a dumb idea because it is less efficient than direct connection charging. Second, it is a dumb idea because of the radiated high frequency radiation. Consider the amount of power being delivered to transfer even 50 KWH of energy in one hour. That is 50 KW. And at 99% efficiency that is still 500 watts radiated. That is enough power to talk all around the world. So there will be huge amounts of radiated interference.

 

So there will be huge amounts of radiated interference.

...... which is highly illegal and will be easily detected by the authorities.

 

...... which is highly illegal and will be easily detected by the authorities.

Consider that some people believe that induction charging of EV batteries is a good idea. At a thousand watts charging level and 99% efficiency that leave 10 watts of radiated power.
In the TS instance, if there is no moving around of any of the coils during the measurement time, Then the power transmitted must be varying. That could be caused by insulation breakdown and arcing, or by circuit instability in the system.
In addition, for charging any sort of full sized electric vehicle battery, or even an ordinary 12 volt battery in a fuel powered vehicle, a much greater voltage will be required.
So before any applicable advice can be provided the TS needs to provide quite a bit more details. What we know so far makes no sense at all.