Car current draw

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.
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On Thu, 31 Jan 2008 12:58:23 -0800 (PST), ransley

No but you could use the Ma scale in series (disconnect the battery, put the meter in line) but don't turn anything else on. You could overload the meter.
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ransley wrote:

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.
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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.
Jerry
Jerry
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ransley wrote:

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.
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My guess is lower than 100mA. If it is higher than 500mA, it is definitely suspicious.
Clamp meter is for high AC current. You are trying to measure low DC current.
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fully charge battery and get it load tested, the simplest answer is usually the solution. how old is your battery? if its over 3 or 4 years its probably bad
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Ransley posted several weeks ago. Original battery in his 2002 Volvo. If memory serves.
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No. 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.
Joe
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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.
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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 ammeter.
Buy a new battery, and quit wasting our time.
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I believe the problem is AC current vs DC current.
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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.
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The more I think about it, the more I believe you are correct.
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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.
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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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