Same chargers?

Wan wrote:


Irish for idiot.

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Hey Six_O'Clock_High You hit the nail right on the head. The Auto charger will fry the hobby charger. Also the warning isn't that clear, some boneheads use a auto charger as a transformer to convert house current to the 12 vdc but the charger dc voltage is too high for the hobby charger.

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It's less to do with voltage and more to do with how steady/clean the current is. Battery chargers are notorious for ripply/noisy outputs that *approximate* true DC.
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The Raven
http://www.80scartoons.co.uk/batfinkquote.mp3
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The Raven wrote:

Nonetheless I tried my Astro on a 90% screwed truck battery with a permanent charger attached to it. It worked as long as the packs didn't demand more current then the charger could deliver. Ther was just enough batteryness left in the truck battery to hold voltage between rectifier peaks I reckon :-) On its own the battery self discharged in a couple of hours off load, or in a couple of minutes with the charger.
Not the way to go permanently - I bought an ex CB PSU on Ebay - but its certainly a way to go in an emergency.
But without the battery nothing got damaged, it just didn't work at all - rectified DC with no smoothing. I didn't have a smoothing capacitor to try...
Both my chargers - AStro 109 and a RipMax Pro Peak - were pants on just the charger. Neither got damaged - it was really cheap nasty DIY motor store charger.
Not recommending it, merely reporting some actual facts.
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Just a guess -- a lot of automotive battery chargers have only a transformer to drop the 110 or 220V AC into approximately 14V AC, and then a gizmo called a bridge rectifier that changes the AC into pulsed (very dirty) DC, which is going from 0V to 14V 50 to 60 times per second. To get clean DC, most power supplies designed for such have a couple of big capacitors after the bridge rectifier that smooth out these voltage fluctuations. However, when a battery is hooked up to one of these cheapo chargers, it functions as a capacitor, and you get fairly clean DC your NiCd/NiMh/LiPo charger needs. Am I correct?
Morris
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| Just a guess -- a lot of automotive battery chargers have only a | transformer to drop the 110 or 220V AC into approximately 14V AC, | and then a gizmo called a bridge rectifier that changes the AC into | pulsed (very dirty) DC, which is going from 0V to 14V 50 to 60 times | per second.
Actually, after a 60 hz AC signal goes through a bridge rectifier, the main component of the signal that comes out is 120 hz, not 60 hz (with lots of other harmonics -- as you said, it's dirty.)
(A minor nit, I know.)
| To get clean DC, most power supplies designed for such have a couple | of big capacitors after the bridge rectifier that smooth out these | voltage fluctuations.
I'm guessing that automotive chargers use some capacitators as well, because the charging only happens when the voltage is higher than the battery's current voltage, and they don't want a charger that only charges 10% of the time.
(And they don't want the voltage to ever go higher than 14.7 volts, because that burns off the electrolyte of Pb batteries. The very cheapest chargers (especially the wall-warts) do go higher, and will burn off your electrolyte if left on, but that's only the very cheapest ones.)
There's probably also a voltage regulator in there, just to make sure that they don't cook your battery with too much voltage. At least in all but the very cheapest chargers.
It also doesn't have to be a capaciator. A coil (or choke, same thing) in series with the signal will have the same effect.
| However, when a battery is hooked up to one of these cheapo | chargers, it functions as a capacitor, and you get fairly clean DC | your NiCd/NiMh/LiPo charger needs. Am I correct?
I suspect you are mostly correct.
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Doug McLaren wrote:

They do if its cheap nasty and used only occasionally.

There is usually a resistor and/or transformer saturation built in to limit the peaks. Basically they limit the current to - say - 3-4A - and given that all car batteries will themsleves accept 10 times higher charge current than that, then despite what the open circiuit voltage is, the battery clamps it to around 13-14v.
In teh past they used copper oxide rectifiers that were nice and resistive, and had cooling finns on em. The one I have appears to have a trashy bridge rectifier, and a wirewound resistor, a transformer that I reckon would de at 5A continuous, and a fuse that blows at 7A or so. :D

Your confidence in the manufactureres of cheap car battery chargres is sadly misplaced :-)

Mmm. Not really.

Yes.
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| > (And they don't want the voltage to ever go higher than 14.7 volts, | > because that burns off the electrolyte of Pb batteries. The very | > cheapest chargers (especially the wall-warts) do go higher, and will | > burn off your electrolyte if left on, but that's only the very | > cheapest ones.) | | There is usually a resistor and/or transformer saturation built in to | limit the peaks.
I'm not sure what you mean by `transformer saturation', but a resistor by itself will not prevent a 15 volt power source from burning off the electrolyte of a 12 volt car battery. It may slow it down, but won't stop it.
| Basically they limit the current to - say - 3-4A - and given that | all car batteries will themsleves accept 10 times higher charge | current than that, then despite what the open circiuit voltage is, | the battery clamps it to around 13-14v.
Yes, but that's the catch -- if the open circuit voltage is over 14.7 volts, and the battery is fully charged, it will start burning off electrolyte, which is bad.
It may very well be that they just don't care -- after all, you don't usually put a high amperage charger on your car battery and leave it there for days. (A trickle charger, on the other hand ...)
| In teh past they used copper oxide rectifiers that were nice and | resistive, and had cooling finns on em. The one I have appears to have a | trashy bridge rectifier, and a wirewound resistor, a transformer that I | reckon would de at 5A continuous, and a fuse that blows at 7A or so. :D
Just for the record, a wire-wound resistor also functions as a choke.
| > There's probably also a voltage regulator in there, just to make sure | > that they don't cook your battery with too much voltage. At least in | > all but the very cheapest chargers. | | Your confidence in the manufactureres of cheap car battery chargres | is sadly misplaced :-)
Could be ... | > It also doesn't have to be a capaciator. A coil (or choke, same | > thing) in series with the signal will have the same effect. | | Mmm. Not really.
Yes, really. A capacitator stores energy in it's electric field, and a coil stores it in it's magnetic field. In a DC circuit with `dirty' power, a capacitator in parallel with the circuit or a coil in series with the circuit will both have similar effects -- to smooth out the current. (Assuming you pick appropriate values of both, of course.)
The coil will introduce resistive losses where a capacaitor usually doesn't, but if you want a resistor in there to limit current anyways, might as well kill both birds with one stone.
I may have to open up my car battery charger and see what's in there. And hook it up to the oscilliscope to see what the output looks like with no battery connected ...
Of course, this thread has drifted pretty far off topic. :)
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Doug McLaren, snipped-for-privacy@frenzy.com
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Doug McLaren wrote:

Transformers whose cores saturate will act as crude voltage regulators.
Look up CVT on google.

They don't.

Yes, burt to vbe effective at 100hz you need a henry or two. A wirewound resitor is microhenries at best.
I am beginning to realise just how slender your grasp of electronics actually is.

You are talking to someone with a masters in electrical and electronic engineering.
Try and work out howto do what you want with just a series choke, and then work out the proce of it compared with an electrolytice

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| > I'm not sure what you mean by `transformer saturation', but a resistor | > by itself will not prevent a 15 volt power source from burning off the | > electrolyte of a 12 volt car battery. It may slow it down, but won't | > stop it. | | Transformers whose cores saturate will act as crude voltage regulators. | | Look up CVT on google.
I did after that post, actually. Well, not CVT, but ...
http://www.allaboutcircuits.com/vol_2/chpt_9/11.html
didn't make it look like this was a good thing, and the secodary wave form looks a lot noisier than it would were the transformer not saturated. But their first figure is obviously is an extreme case, and I can see where if it wasn't so saturated that things would be better. Still noisy though.
Do they really intentionally saturate the transformer in a power supply like this? It doesn't seem like a very efficient way of doing things -- but I guess when low cost is your main objective ...
| > Just for the record, a wire-wound resistor also functions as a choke. | | Yes, burt to vbe effective at 100hz you need a henry or two. A wirewound | resitor is microhenries at best. | | I am beginning to realise just how slender your grasp of electronics | actually is.
Oh, I admit it, my electronics knowledge is far more theoretical than practical. My degrees are in physics and astronomy, not electrical engineering. I never claimed to know everything. Not even close.
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Doug McLaren, snipped-for-privacy@frenzy.com
Time may be a great healer, but it's also a lousy beautician.
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Morris Lee wrote:

Yes. On the button.

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one says can use automobile BATTERY, the other says CHARGER...;-)

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snipped-for-privacy@toast.net (Wan) wrote in message

Reread it carefully. The advice is not differing, and does not conflict.
You can use a car BATTERY to power the charger.
You CAN'T use a car battery CHARGER to power the charger.
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This first charger uses a 12V power source and will probably run off any decent 12VDC supply.

Home battery chargers do not produce a well regulated 12VDC supply. It may measure around 12 volts but it's far from pure DC. Consider it dirty DC.

Get the charger you desire but ensure the power supply (assuming 12VDC) is clean DC. Best source for that is a charged automotive battery or a modified computer power supply (computers require clean supplies).
--
The Raven
http://www.80scartoons.co.uk/batfinkquote.mp3
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