The voltage you are seeing is tiny.
It will be coming from the capacitors in the radio and alarm that were
charged when the battery was connected.
voltage from those will be leaking back through the circuitry and seen
by the meter.
Because the route through the various components is high resistance it
drops as the meter loads it up then recovers from the capacitors when
you remove the load.
Don't worry about it, it's normal.
Jim
On 24/05/2010 22:32, Susan and Martin Scott wrote:
I'll try putting the ammeter in circuit tomorrow. What i can't
understand is why there is a voltage without the battery connected?
Martin
----- Original Message -----
*From:* Jim Hearne <mailto:[email protected]>
*To:* [email protected]
<mailto:[email protected]>
*Sent:* Monday, May 24, 2010 10:23 PM
*Subject:* Re: [Quantum Owners] Battery drain
At the others have said, you need to measure the current drain
from the battery by removing one battery lead and connecting the
meter between that and the removed wire.
Do not even turn on the ignition.
A typical current drain with a car radio and alarm will be below
20ma (0.02a), anything over 50ma indicates a problem and will
flatten the battery.
Isolate the problem circuit by removing fuses until the current
drain disappears.
Jim
On 24/05/2010 21:53, Susan and Martin Scott wrote:
Sorry I forgot to say both were new batteries. The first battery
was new last year, when the car was finished. The battery was
flat after being left 2 weeks, and I thought it was a faulty
battery. It was replaced, and I kept the battery on charge in the
garage on a smart charger over Winter.
The car drove to Stoneleigh and home no problem (left overnight
with alarm on as well during weekend). The week after (having
been used off and on I started and moved it on the Friday, on the
Sunday I went to open the boot and the battery was dead flat. It
was replaced again (a good supplier!), but I can't expect to rely
on their generosity again, and I need to be able to have
confidence that all will be ok.
----- Original Message -----
*From:* Derek Clews <mailto:[email protected]>
*To:* [email protected]
<mailto:[email protected]>
*Sent:* Monday, May 24, 2010 9:03 PM
*Subject:* Re: [Quantum Owners] Battery drain
Hi. If you have a possible problem with the battery, try
disconnecting the battery (and remove from the car if
convenient) just charge via a mains charger and then check
the voltage after a good charge and over a period of time
after. If it goes down to below 12V sitting over a day or
two it is shot. You cannot get a real view of the battery
while connected it may be a drain from the car. This has
worked for me with cars and the canal boat. (four batteries
in two banks!)
Alternatively, try and see what AMPs are flowing out of the
battery when everything is switched off. You may need to
read the manual with your meter to see how to connect this or
even if your meter is suitable. But would be in line between
one terminal and the lead, not across the two battery
terminals. There may be legitimate drains on the battery.
e.g. a car alarm or an interior light on. I have had a
failed light switch before so the boot light was on all the
time. I traced it that way.
If you are checking the battery the first way is really the
business. That way you can really confirm it's OK.
Alternatively your can take it to a specialist who will test
it under load and see if it is weak. The second way is more
for car fault finding.
Derek
On 24 May 2010, at 20:39, Susan and Martin Scott wrote:
I've now had a second battery replacement, and have
therefore come to the conclusion that it may not be a fault
with the battery. The last time it drained to nothing in 2
days (and it was absolutely nothing, not even enough to
light an LED!). I immediately detached the terminals and
found there was no resistance - indicating nothing in circuit?
Although I'm confident with simple circuits, I'm the first
to admit that electronics is beyond my brain
power................. I set about some detective work today
Findings 1. With meter set on ohms, I get no reading across
the battery terminals when disconnected from the battery and
nothing in circuit.
2. With the battery terminals connected and the engine
running the voltage across the terminals is 13.7V
3. Without the engine running the voltage across the
battery is 12.6V
4. With the battery terminals disconnected and the meter
set to 2V, I found there was a voltage of 0.048V when the
meter was connected, which reduced to level out at 0.015V.
It didn't seem to matter when the meter was connected ie If
I measured across the terminals 3 Sec after disconnecting
from the battery it was the same as if I waited 2 minutes,
and also the drop once the meter was put across was delayed
if interrupted eg . 0.048 then watch it drop to 0.030,
remove meter for 5 seconds, reconnect meter and the reading
was 0.030, then dropped further.
5. Having removed all the fuses, the same occurs.
The alarm fuses have been disconnected as well, but I
don't think it has a battery in it.
6. Connecting the meter between the engine block and the
positive battery terminal measures a lower voltage 0.028V,
which drops to the same 0.015V
Is it maybe electrolytic reaction within the block? As I say
I'm not into electronics.
Why is there no measured resistance, but the battery drains?
Any ideas gratefully received.
Martin
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