How does a multimeter work?

[DaveDreads]

My battery was flat yesterday and I need to check if the alternator's charging it properly,
it should be because it's brand new, i'm thinking the battery running flat and recharged a few times has knackered it.

A bloke I know has lent me this, but I don't know what setting to put it on to check the battery,
what should I have it on?

 

[LIL B]

DCV

 

[JohnnyE]

Put it on volts dc and battery should read between 12 and 13 volts

 

[DaveDreads]

In DCV there's 500, 200, 20, 2000m & 200m, which one should I use?

 

[BIGASH]

20

 

[Jaff.]

Does it not have auto range?

​my bad, just looked that the picture. 20 willdo it

 

[Cup_Phil]

Crikey

Put it on 20 and put the red to the battery positive and black to battery negative
It should read 12 to 13v without the alternator running for a healthy battery
With the alternator running it should run around 14v

 

[DaveDreads]

Crikey

I take it you were born with the ability to decipher electronic settings
and use a multimeter then?

The last one I used didn't have a dial, just a needle that told you what volts it's putting out,
I don't have an electronics degree so don't know what any of it means.

The alternator's hovering around the high 14s, as is the battery with the engine running,
with the engine off the battery's hovering around the low 13s.

The fact that it was flat yesterday probably means I need a new battery as it's obviously not holding it's charge.

 

[Jaff.]

Does the voltage at the battery drop at all when you're holding the meter on it?

got a battery centre local? Ask them to drop test it for you, will give you a definite answer then as to wether your battery is shagged

 

[DaveDreads]

Yeah it started at 18 and levelled off at about 13v, it was still dropping but only by 0.1 every 20 seconds or so.

 

[Jaff.]

When its shut down I mean now...

if it drops about 0.01 v every second or so its shagged. I'd find a drop tested to be sure of it though. Will tell you in seconds if you need a new oneone

 

[DaveDreads]

That was with the engine off mate, looks like I need a new one then,
it'll have to wait until next week though as i'm out of tax and get paid at the end of the week.

​Why does sh*t always f*ck up when you're skint?

 

[Jaff.]

Called Sod's law mate.

​Get it drop tested to be sure before spending any money, you may just have a drain on the car somewhere that could be a cheap fix

 

[mharvey]

I had to buy a battery the other week

I'm sure you'd rather hear that you don't need one but if you do the battery I bought was a Bosch S5, really highly rated but expensive. However I found it on ebay (brand new from a shop on there)for £56 delivered. Seller was brilliant too.

 

[DaveDreads]

Part of me just thinks that going to a battery place to have it tested will just end up with them selling me a new one,
I can't imagine they're going to say 'nah it's fine mate, keep your money'.

I don't even know what a drop test is.

 

[Jaff.]

My local place told me it was ok and actually told me the issues I was having was probably due to the cold weather.

its worth asking. If its free it costs you naff all and you might save yourself buying a new battery

 

[Cup_Phil]

I take it you were born with the ability to decipher electronic settings
and use a multimeter then?

The last one I used didn't have a dial, just a needle that told you what volts it's putting out,
I don't have an electronics degree so don't know what any of it means.

The alternator's hovering around the high 14s, as is the battery with the engine running,
with the engine off the battery's hovering around the low 13s.

The fact that it was flat yesterday probably means I need a new battery as it's obviously not holding it's charge.

It wasn't you I was saying crikey at - it was the people saying 12-13vv means alternator is fine lol

Yes if you're getting those readings then alternator is absolutely fine so battery isn't holding the charge
As for it being due to cold weather - yes it takes more to crank an engine in the cold but it still means your battery is knackered

Find someone with a halford trade card - cost you about £40

 

[Jaff.]

It wasn't you I was saying crikey at - it was the people saying 12-13vv means alternator is fine lol

Yes if you're getting those readings then alternator is absolutely fine so battery isn't holding the charge
As for it being due to cold weather - yes it takes more to crank an engine in the cold but it still means your battery is knackered

Find someone with a halford trade card - cost you about £40

Battery on the bmw used to go flat enough that it wouldn't start the car. Drop tested fine. Was a bit low voltage wise but nothing too bad. So cold weather can hinder a battery.

​this may well be a different issue though.

 

[DaveDreads]

It wasn't you I was saying crikey at - it was the people saying 12-13vv means alternator is fine lol

Oh right, sorry Phil.

 

[Cup_Phil]

Battery on the bmw used to go flat enough that it wouldn't start the car. Drop tested fine. Was a bit low voltage wise but nothing too bad. So cold weather can hinder a battery.

​this may well be a different issue though.

Voltage isn't the same thing as ampage. If the battery was on the way out it wouldn't have enough cold cranking amps to start the engine. Common issue on diesels as they have to crank the diesel pump too so if they don't quite crank fast enough they won't start.

Oh right, sorry Phil.

No apology required, my reply was badly worded

 

[Jaff.]

Voltage isn't the same thing as ampage. If the battery was on the way out it wouldn't have enough cold cranking amps to start the engine. Common issue on diesels as they have to crank the diesel pump too so if they don't quite crank fast enough they won't start.




No apology required, my reply was badly worded

it wasn't cranking at all! Turn the key to ignition on and all you get was a few clicks of a few relays.

doesnt matter anyway its not even cold so Davies issue is probably different

 

[Dink]

a drop test is the only real way to find out if it's duff

as you can still get full voltage on a duff battery

 

[DaveDreads]

Can someone please explain what a drop test is?

 

[Jaff.]

http://www.aa1car.com/library/voltage_drop_testing.htm

​basucally checking what the battery is up to when its being used the most

 

[DaveDreads]

Well the thing's sat on the drive for the past 8 days because of no tax,
the battery was fully charged when it went in, it started first time so I went down the petrol station,
when I got back into the car the battery was flat.

It eventually started after a couple of attempts, so it's safe to say it's not holding a charge anymore,
​unless something's capable of draining it in 8 days?

 

[Big Bob]

Hey where you based ill look at it for ya for free and i dont sell batteries, i have a degree in electrical and electronic engineering and have all neccesary equipment you could need.

 

[DaveDreads]

Cheers mate but i'm in Coventry, a mate of mine has a garage in the next town,
so i'll go and see him tomorrow and have the battery drop tested.

I was just wondering if anything on the car could drain the battery in 8 days?

The only thing I can think of is the boot light or something,
but seeing as the battery went flat and was recharged about 8 times when the alternator was f*cked,
​i'm assuming it can't hold a charge any more.