Chief Delphi - possibility to use charger and battery at the same time

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Re: possibility to use charger and battery at the same time

Quote:

Originally Posted by MrForbes (Post 1449304)

You read my mind. Although I was just going to do it with a volt meter, since my scope probe got lost on the movie set, and I haven't replaced it. Maybe an analog voltmeter, because it would be so neat to show the students some old technlogy. And I was wondering last night where I put my dad's voltmeter...I found it around 1 AM. Won't see the little transients, but will give us an idea of what the charging voltage is.

You could film it.

Re: possibility to use charger and battery at the same time

Quote:

Originally Posted by MrForbes (Post 1449290)

How good of a filter is the battery?

Most batteries are good low-frequency filters, but they don't do much to reduce high-frequency noise or transient spikes -- or the kind of intentional pulses one gets from a "smart" charger.

I'm going to modify my earlier advice. Don't use a battery charger to power a circuit unless 1) the charger is designed for it, and 2) the circuit is designed for it.

Re: possibility to use charger and battery at the same time

I did a little poking around with a couple battery chargers. I have a modern charger

http://www.amazon.com/Schumacher-XC6.../dp/B004EIBX00

which I used to charge a battery that had been sitting for a while. It started charging at about 14v and after several seconds the voltage increased gradually to about 16v, then slowly went down to around 14 as the battery charged. I found an old probe and connected my scope, and did not see anything resembling pulsing, transients, etc. The analog voltmeter also didn't show anything to get concerned about.

I also visited the robot room today, and brought my analog volt meter. We have old KOP chargers, which do pulse the battery, as indicated on the "charging" light changing color from green to orange. Video

http://youtu.be/Vf4AfdQVWRo

Maybe it's not as bad as we might think?

Re: possibility to use charger and battery at the same time

If a battery charger is a quality unit it won't provide pulse voltage unless it has a de-sulfite mode. As noted though some will provide a fairly high equalize charge voltage.

Re: possibility to use charger and battery at the same time

We have checked battery chargers here at work over many years and several battery technologies. If one just checks the charger connected to a battery, you will find a fairly steady voltage with little transients when the impedance of the connection is low and the battery is almost charged. (Remember that battery internal impedance varies with state of charge) However, the smart chargers are designed to sense battery delta voltage and will regularly switch from charge to sense. If there is any impedance in the line, there will be significant "noise" generated in high impedance paths as they exist. Lead/acid technologies generally perform "constant voltage" charging which by definition is not a low impedance path. The KOP chargers and most of what has been discussed, has #16 or #18 wire which compared to the battery adds significant impedance as well. The addition of a scope probe also grounds the circuit through the scope so that noise that is present may be removed by the method used in examining the noise. Differential scope methods should be used when examining this circuit.