OT - Charging circuit on small gas engines

You can run a battery charger from the AC side.

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The one for the other onan engine should likely fit.

16 to 16 volts open circuit would not be a problem if the battery voltage never goes over 14.4. You could always add another diode in series to peel off another 0.7 volts

That is a Clue!

Refer to Clue above. I suspect that the charging circuit is heavily current - limited and would not supply sufficient current into the very low impedance of a properly sized battery to cause harm.

I would borrow a battery from one of my fleet vehicles and place an ammeter in series, between it and the charging circuit. Chances are that the current reading is quite low and that the battery voltage never would get above a safe level.

--Winston

DC circuits have zero impedance

Unfiltered DC, such as coming from a magnet passing a coil, is DC because it never changes direction of flow, but the voltage does change, creating a back EMF and an impedance in inductive circuits. It's DC, but alternating DC, just like a rectifier on the output of a transformer.

No, they have zero _reactance_; the impedance is simply equal to the resistance, which is the real component of impedance, which is a complex number.

Hope This Helps! Rich

Sooo.. you're saying a (non faulty) capacitor has zero reactance at DC?

Best regards, Spehro Pefhany

DC circuits eventually settle to voltage and current values determined by resistance, regardless of their reactance which can be considerable. Impedance is the combination of resistance and reactance, as Rich wrote. For 12V lead-acids the temporary surface charge of about a volt also affects the charging current.

When testing the "45W" HF solar panels I found a bad Hawker Cyclone that I hadn't been charging as the article recommends.

BTW the solar panel rating is misleading, They produced nearly their rated current but the rated voltage to get 45W is 17.5V which they may well reach but not when directly connected to a 12V battery as with the included controller. I saw 32W, still not bad for February in NH. The local store had them at $159 and I got some more off for taking a crushed box. They tested OK for open voltage and shorted current in the parking lot.

I bought a bunch of the cheap HF multimeters for battery and auto work. The 10A range is good enough to check small-engine charging currents and if I fry one I'm out only $3 - $5. I checked two against good lab voltmeters last night and found they were about 5 counts off,

50mV at 10V, which doesn't really matter for 12V lead-acids.

jsw

Of course not, you nincompoop. A capacitor is an open circuit at DC, so the concept of impedance is meaningless.

Hope This Helps! Rich

Rectifying the output of a small engine's alternator and feeding straight to the battery is very common. Nearly all of the smaller Japanese motorcycles are made that way, sometimes with the addition of a switchable resister, wired through the light switch, so that alternator output is reduced a bit for running without the lights.

What I'd is to fire things up and check the voltage at the battery terminals, if the actual battery voltage doesn't get over about 14 volts then I wouldn't worry about it. My guess is that you'll be getting closer to 14 volts with the engine running.

Actually, the _susceptance_ approaches zero as f->0 (susceptance is 1/reactance),

The reactance of an inductor approaches zero as f->0 (susceptance heads for the roof)

Immensely, Rich. WTF are you doing up at 5AM CA time anyway?

Best regards, Spehro Pefhany

Right, but this isn't a 'pure' DC circuit.

By mentioning 'impedance' instead of just ESR, I hoped to remind us that the current waveform into the battery is dependent on it's Equivalent Series Resistance *as well as* how it 'looks' to the pulses of D.C. from the rectifier, in the frequency domain.

See for example, Table 1 of:

Here is a gross example to show the effect.

If you load the following circuit into LTSpice, you can vary the inductance of L1 to change the inductive reactance seen by the generator winding. (The circuit shows the output of the 'battery charge' winding in series with a rectifier, a 1.0 mH inductor and a battery that has an ESR set to 1.2 milliohm. The generator is running at 3600 RPM).

Note that I am *not* saying that the inductive reactance of any healthy battery is *anywhere* near as high as shown in this circuit. I'm just showing that pulsed D.C. faces more 'opposition to flow' than that posed by simple resistance.

Even with the D.C. resistance of the inductor fixed at zero, the peak current into the battery will be inversely proportional to the inductance of L1 (in addition to the ESR of the battery and the effect of the forward drop of the rectifier).

Version 4 SHEET 1 1276 680 WIRE 32 144 -64 144 WIRE 224 144 96 144 WIRE 336 144 304 144 WIRE 336 192 336 144 WIRE -64 256 -64 144 WIRE 336 304 336 272 WIRE -64 368 -64 336 FLAG 336 304 0 FLAG -64 368 0 SYMBOL voltage -64 240 R0 WINDOW 3 13 107 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value SINE(0 22.6 60 0 0 0 5) SYMATTR InstName V1 SYMBOL voltage 336 176 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMATTR SpiceLine Rser=1.2m SYMBOL ind 208 160 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 5 56 VBottom 0 SYMATTR InstName L1 SYMATTR Value 1m SYMATTR SpiceLine Rser=0 SYMBOL diode 32 160 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 TEXT -80 416 Left 0 !.tran 0 .1 0

--Winston 'Z is the word is the word is the word..'

The test I've seen and done for battery impedance is to measure the voltage at a steady low-level current, then pulse on a higher load and capture the voltage and current waveforms on a digital storage scope. The impedance is the slope of the line between the low and high current V and I, at a place on the waveform chosen by the battery engineer. The higher frequency effects which are relevant to PWM motor drivers are easily removed with capacitors. The low frequency impedance (mostly resistance) is a good measure of the condition of the battery.

jsw

(...)

Note how Hawkins and Barling used a one-step process for each frequency of interest with their very low impedance measuring circuit.

forcing a small, levelled, alternating broadband current through the battery, they measured the resulting voltage between 5 milli-Hz to 100 Hz in order to arrive at an impedance reading, calculated by an attached PC. They went on to measure impedance above 10 Hz (to 100 KHz) using current-levelled sinewave excitation.

Impedance scaled directly with the voltage - to - current ratio at any given frequency. Because current was known and held constant, Z was directly proportional to V. Kewl!

Abso-tively.

--Winston

There's no real work for me (I do autocad and geek stuff), so I get to sweep the floors and take out the trash and clean the sinks and toilets, and in exchange they let me sleep in the office rent-free and eat donated food. (I got evicted when I went broke and couldn't pay the rent.)

Occasionally I get some real work, but the company can't afford to pay me money until about next April; they're behind on the rent as well, but the landlord is a freakin' angel or something. :-)

Cheers! Rich

Well, lessee - 0.050 / 10 is, what, a half a percent? That's pretty good for a three dollar meter! ;-)

Cheers! Rich

Did it seem to you that they might have been measuring the response of their test setup in addition to the batteries?

jsw

The Keithley and Fluke agree to +-1mV. Their last calibrations were in

1994 and 95.

jsw

Oh, of course, no question! But you're not going to get a Keithley or Fluke at Harbor Freight for three bucks! ;-)

Cheers! Rich