What should the current draw be with a car parked, for the night, not
running, Volvo v40 with factory alarm but never activated. How do you
check this. In the morning my battery is low. Can I use a 120v digital
clamp on amp meter.
I use the amp meter on a digital car multimeter. Normally, when not
running and key off, a car pulls just enough current to keep the
computer and the digital stereo settings alive, which isn't much. I
don't know exactly how much but I would bet it's way below a half an amp.
In any case, to track down a current leak, attach an amp meter and start
pulling fuses until you find the one that is pulling excessive current.
Note that if you do this on a recent Honda, you'd better have the
radio security code before you pull all power to the radio. When the
power comes back on, you have to enter the security code to activate
the radio. If you don't have the security code, you need to take the
radio serial number (located, of course, on the back of the radio) to
the dealer for them to look up the security code. It has been reported
in several Honda forums that some less-than-consumer-friendly dealers
have been charging for this information.
Volvo may or may not do this also, I don't know.
You should expect a standby current of perhaps .1-.2A at most, composed
of the ECM, radio, alarm and any feature module standby demands.
A clamp on amp meter will only work if it is the AC/DC hall effect type.
Even then, the expected current draw is so low that a clamp meter
wouldn't work well. You will generally need to disconnect a battery lead
and connect the meter in series using the appropriate connections for
it's DC Amp range.
Something as simple as a failed switch on a trunk or hood light keeping
it on will greatly increase the standby current. If the standby current
looks reasonable then the suspects are the battery and the alternator.
Other more unlikely suspects would be stuff like air suspension
compressors running periodically due to a leak, or a power radio antenna
continuing to run after it's down due to a bad limit switch. I don't
know what a Volvo v40 has so no idea if any of those are applicable.
Use a decent digital multimeter. Turn everything off, make a
connection to the battery negative cable and the battery negative post
(it can be done, be clever) and loosen the negative battery cable
clamp. With the meter set on MA, quickly slide the cable off the post,
take the reading and put the cable back on. For typical vehicles the
reading will be around 30-40 MA (YMMV). This technique won't screw up
fussy alarms, radio anti-theft codes and all that. When you get it
back together, check the charging voltage, which should be around 13.8
at idle, rising to 14.6 or so at 2000 RPM. If the system checks are
all good, read the Consumer Reports on batteries and go shopping for a
new one. Good luck.
Maybe if you told us why you are wanting to measure the current, we
might be able to give you some more direct help.
I will add that some cars will draw a lot more than usual dark current
right after they are shut down. Five or ten minutes may be needed before
they are down to static mode. And no you can't use an 120V meter which is
likely an AC only meter.
Maybe my clamp on ammeter is defective. It doesn't specify 120 volts. I've
been using it on both 110 and 220. Maybe if I have to read 220, I need to
cut the amp reading in half?
You'll have to go to the auto parts store, and buy a 12 volt clamp on AC
Buy a new battery, and quit wasting our time.
I don't really know whether the usual retail/consumer grade
clamp-on meters will do DC. But the ones that auto mechanics
use _will_ do DC readings. I've watched one in use testing
a battery/charger - they're not AC only.
These meters don't care what voltage they're measuring. All they
know is magnetic field strength around an individual wire,
and that depends solely on current, not what the voltage is to some
other wire that's arbitrarily far away.
Age and Treachery will Triumph over Youth and Skill
How old is the battery? It may not be the parasitic draw, it may just be
the battery slowly heading south. You can try disconnecting the battery and
see if it is weak in the morning. If so, replace it.
Someone said they thought the battery was from 2002. If that's the
case, personally, I'd just replace it. That's near the end of normal
life for a battery. Even if it's not on it;s way out, I'd rather do it
as preventative maintenance, when it's cheap and easy, rather than get
stuck somewhere and have it cost a lot more.
He can also get the battery tested at some auto stores, Autozone is
one that does it for free I think.
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