OT -- charging by generator

I know nowt about generators but maybe someone can help.

I've just bought a cheap generator that outputs 12v/8.3A for battery
charging.

Does anyone know how long this would take to charge a Series 3 battery?
And is there enough power to use it to jump-start the car (I guess
there's not).

On Mon, 5 Sep 2005 10:45:19 +0100, Web Sniffer
<[email protected]> wrote:

>I've just bought a cheap generator that outputs 12v/8.3A for battery
>charging.
>Does anyone know how long this would take to charge a Series 3 battery?

Look at the Amp Hour rating for the battery. Divide that by the
output of the genny. (55Ah battery / 8.3A = ~6 to 7 hours).
This is not a precise science - the math may not be known to the
battery concerned ;-)

>And is there enough power to use it to jump-start the car (I guess
>there's not).

No.

Web Sniffer wrote:
>
> I know nowt about generators but maybe someone can help.
>
> I've just bought a cheap generator that outputs 12v/8.3A for battery
> charging.
>
> Does anyone know how long this would take to charge a Series 3 battery?
> And is there enough power to use it to jump-start the car (I guess
> there's not).

Charging a battery from a generator is not a particularly good idea if
the DC is rectified from AC. This is because the rectified DC is likely
to have high levels of AC ripple superimposed and batteries don't like
that. You can alleviate this, to a certain extent, by adding a large
capacitor across the DC output terminals of the generator.

Another thing to consider is that if the genny really is a cheap one (as
opposed to an expensive one purchased cheaply) then the DC may only be
half wave rectified and that will probably kill your battery rather than
charge it.

If the genny output really is 12V DC then it won't fully charge the
battery anyway - that needs something more than 13.5V.

As for using the generator to jump start the vehicle; I doubt that will
work. The DC current needed to start any vehicle is several hundred
amps. Unless the generator has short circuit overload protection I
wouldn't even attempt it.

Of course, there will be a generator/battery charging expert along in a
minute to quash all of the above

--
Regards

Steve G

"> Charging a battery from a generator is not a particularly good idea if
> the DC is rectified from AC. This is because the rectified DC is likely to
> have high levels of AC ripple superimposed and batteries don't like that.

That is not correct, in fact some charger eithe deliberatly superimpose AC
or pulse the DC.
The theory is that the AC causes the gas bubbles on the plates to disperse.
In fact most simple mains chargers have no smoothing, their output is
straight raw rectified mains.

Snip>
> If the genny output really is 12V DC then it won't fully charge the
> battery anyway - that needs something more than 13.5V.

More like 14 -14.5V to fully charge a battery.

>
> As for using the generator to jump start the vehicle; I doubt that will
> work. The DC current needed to start any vehicle is several hundred amps.
> Unless the generator has short circuit overload protection I wouldn't even
> attempt it.

Agree totally with that.

Regards
Jeff

Mother <"@ {mother} @"@101fc.net> wrote:

>>And is there enough power to use it to jump-start the car (I guess
>>there's not).
>
>No.

But it should be enough to use it to fill the battery for maybe 30
minutes and then try to start the car.

Jeff wrote:
> "> Charging a battery from a generator is not a particularly good idea if
>
>>the DC is rectified from AC. This is because the rectified DC is likely to
>>have high levels of AC ripple superimposed and batteries don't like that.
>
>
> That is not correct, in fact some charger eithe deliberatly superimpose AC
> or pulse the DC.
> The theory is that the AC causes the gas bubbles on the plates to disperse.
> In fact most simple mains chargers have no smoothing, their output is
> straight raw rectified mains.
>
SG: See I knew someone would have the real story. I guess I made a bad
assumption that car batteries behaved like the ones we use in DC UPS
systems. Ya learn summat every day )

> Snip>
>
>>If the genny output really is 12V DC then it won't fully charge the
>>battery anyway - that needs something more than 13.5V.
>
>
> More like 14 -14.5V to fully charge a battery.
>
SG: Agreed, I was just trying to say that 12V won't do the job.
>
>>As for using the generator to jump start the vehicle; I doubt that will
>>work. The DC current needed to start any vehicle is several hundred amps.
>>Unless the generator has short circuit overload protection I wouldn't even
>>attempt it.
>
>
> Agree totally with that.
SG: Phew! Got something right anyway



--
Regards

Steve G

In article <[email protected]>, Jeff <[email protected]>
writes
>
>"> Charging a battery from a generator is not a particularly good idea if
>> the DC is rectified from AC. This is because the rectified DC is likely to
>> have high levels of AC ripple superimposed and batteries don't like that.
>
>That is not correct, in fact some charger eithe deliberatly superimpose AC
>or pulse the DC.
>The theory is that the AC causes the gas bubbles on the plates to disperse.
>In fact most simple mains chargers have no smoothing, their output is
>straight raw rectified mains.

Asymmetric AC is _recommended_ for charging many types of battery,
including NiCds and Lead-Acid.

I once saw a very big and very expensive NiCd battery become very
quickly knackered by charging it from a solar panel - steady DC.
And before someone jumps in, it wasn't being overcharged and it was
top-uppable with distilled water. What killed it was dendrite formation
- at least one of the cells went short-circuit.

Regards,

Simonm.

--
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, UK INDEPENDENCE PARTY, BRISTOL www.ukip.org
EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq
GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/

In article <[email protected]>, SteveG
<_@_._> writes
>Jeff wrote:
>> "> Charging a battery from a generator is not a particularly good idea if
>>
>>>the DC is rectified from AC. This is because the rectified DC is
>>>likely to have high levels of AC ripple superimposed and batteries
>>>don't like that.
>> That is not correct, in fact some charger eithe deliberatly
>>superimpose AC or pulse the DC.
>> The theory is that the AC causes the gas bubbles on the plates to disperse.
>> In fact most simple mains chargers have no smoothing, their output is
>>straight raw rectified mains.
>>
>SG: See I knew someone would have the real story. I guess I made a bad
>assumption that car batteries behaved like the ones we use in DC UPS
>systems. Ya learn summat every day )

They don't like smooth DC either - see my other post and the rest of the
thread.

Incidentally, given how much is known about cell chemistry these days,
one has to wonder in the case of some types of battery if the poor
charging regimes aren't deliberate, forcing one to replace cells that
would last far longer if well treated.

Regards,

Simonm.

--
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, UK INDEPENDENCE PARTY, BRISTOL www.ukip.org
EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq
GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/