AC/DC problem

you need a precision rectifier. look that up on the net. you'll find lots of examples. as far as you forcing both - and + to + only, how would you decide on which direction it's going? i guess you could use 2 half wave precision rectifiers..

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Thank you for your time and very good help allready. a few comments to your replies. Yes, agree that the correct name must be "absolute value " Have now looked for precision recifiers,, have simply forgotten to use the web.. happens now and then.. The polarity ; using an opamp with high or open loop as polarity detector. the polarity gives output for count up/down circuits. The final data means, hmm if I understand the question correct then ; In small solar systems, the charge and discharge of the batteries will give much information to the owner on how much there can be used , furthermore, you can decide if more batteries is usefull or you need more solar panels. I'm aware that the voltage level I used, could be a problem but then I got some good ideas from you. :) think I will be able to accept 50mV drop across a shunt , for 20 Ampere This would give a loss of 1 watt ,and the voltage drop will still be without any influence on the system. The presicion is not that important as it will be a problem to know exactly the efficiency in the battery, witch I guess, also varies with temperature, and how big current that is drawn ,and maybe other factors too. but the better the counter works the better result after all. Alex

How many are you making? If it's only a handfull look real hard at hall effect current sensors. Allegro has IC style ones in the current range you are talking about.

Easier output voltages.

Also remember your effirncy error is going to accumulate as you run, probably quite quickly.

Robert

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Want to avoid all these problems ?? I posted a link to a hall effect current sensor that works for AC or DC a few weeks ago, with models rated from 20 to

100 amps .. all of which give a 0-5v output -- stick one on the charging circuit feed to the bank.. stick another on the output side and monitor both currents independently... have your microcontroller ADC the 2 values and compute the difference for net charge/discharge rate

I could dig up the link again if you are interested

Also

Thanks again for new inputs.. thank to John Barret and Robert Adsett for giving me the idea of using hall element sensors.. have asked for samples at Allegro allready.. they seem a good choise for the project, as I can omit the DC/DC supply to the "absolute value amplifier "too. And the currents can be quite high without problems . (the "high end current sensors" from Maxim was considered earlier in the design, but the one that gave out polarity was not to get anymore, and this circuit was not used because of this.) The texas link from GPG is very intersting.. the device checks all about the battery ,too bad its only for LIon batteries.. The efficiency faktor is a problem that I had given some thoughts.. think the Ah monitor have to be reset now and then to get a usefull picture of the charge/discharge. beside an adjustment of discharge / charge is added, so the owner can find a point where the meter will show a usefull result over longer timeinterval. I will return when I have found a solution Thank you all for help. Alex