Alternator/battery tester

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Petrol Pete

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C55 AMG Wagon
Got this from Lidl . £2.99 !! OK, it appears to be made out of cheese, but if it correctly diagnoses a faulty alternator or faulty battery once , it will have paid for itself,, no ? 3 year warranty .
IMG_1741.JPG

I tested it on my van and it does what it says on the (crappy) packaging . Two hundred and ninety nine English pence. !
 
I couldn’t resist getting one last time.
It’s a good simple go/no go, and these will often also indicate when a rectifier diode has gone and the charging system is marginal.
Cracking value.
 
Got this from Lidl . £2.99 !!

Looks about the same quality as the one I got the other day in Halfords for £14!

Sorry to hijack this thread - but I used my £14 one today and got a reading of 12.3 (it only gives numbers, as opposed to good / bad / really bad statuses).

Is that a good reading? And am I right in saying that this number doesn't tell you how much your battery is charged? I think my battery is low, so I was expecting a much lower reading - but I don't really know how these things work.
 
12.3 is not bad at all if the engine isn’t running. Some will say it should be higher but my experience is that given the coldish weather and where we are at the end of winter.
Resting voltage is a good indicator of state of charge, but you do need to factor in meter accuracy amd ambient temperature. The best method is with a hydrometer if you can get to the acid in the battery.
 
12.3 is not bad at all if the engine isn’t running. Some will say it should be higher but my experience is that given the coldish weather and where we are at the end of winter.
Resting voltage is a good indicator of state of charge, but you do need to factor in meter accuracy amd ambient temperature. The best method is with a hydrometer if you can get to the acid in the battery.

Thanks for the insight - I got 12.3 with the engine off having just driven about 20 miles on a cold day.

Do you know how I can find out how much the battery is charged? For example, my phone tells me the percentage of battery remaining - are car batteries similar in that regard, and is it possible to find out how much battery is left? I was hoping to find this out before giving it a full charge with my new CTEK device!
 
The only real way to check state of charge is to use a hydrometer.
There are a number of variables on battery capacity - state of charge, battery health - measured by volt drop under load, and ambient temperature.
You should measure the voltage at least an hour after you have stopped, preferably 12 hours as the battery can have a higher ‘surface charge’ after it has been charged.
Also, don’t forget that your meter may be inaccurate.
 
The world of batteries is a strange and mysterious one where there are no absolutes.

I read a 2-sided A4 article about battery testing and the conclusion was "charge it up overnight and if it doesn't start the car in the morning, throw it away"

Sounds fair enough...
 
The only real way to check state of charge is to use a hydrometer.
There are a number of variables on battery capacity - state of charge, battery health - measured by volt drop under load, and ambient temperature.
You should measure the voltage at least an hour after you have stopped, preferably 12 hours as the battery can have a higher ‘surface charge’ after it has been charged.
Also, don’t forget that your meter may be inaccurate.

Thanks for the tips. I'm not experiencing any issue in particular, I was just curious and want to learn more about it as I don't drive much and sometimes, if I haven't touched it for a few days, it feels like the car isn't going to start. So I'm just trying to clue myself up a bit more, in preparation for the day it doesn't start!

"charge it up overnight and if it doesn't start the car in the morning, throw it away"

The car or the battery? :p
 
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Just fyi, I’ve recently changed the battery on my Jeep. Was reading anywhere from 11.8-11.5 in the morning (based on my fag lighter plug in voltmeter) and still started fine but had started throwing up spurious errors.
New battery shows 12.1-12.2 in the mornings.
There will always be a small voltage drop on a circuit like this as opposed to direct battery connection due to other circuits are consuming current.
 
Do you know how I can find out how much the battery is charged? For example, my phone tells me the percentage of battery remaining - are car batteries similar in that regard, and is it possible to find out how much battery is left? I was hoping to find this out before giving it a full charge with my new CTEK device!

Car batteries are different in that when the engine is running the discharge (as occurs on your phone) is countered by the alternator's charging. Think of it like having your phone hooked to its charger while you use it.
 
Just fyi, I’ve recently changed the battery on my Jeep. Was reading anywhere from 11.8-11.5 in the morning (based on my fag lighter plug in voltmeter) and still started fine but had started throwing up spurious errors.
New battery shows 12.1-12.2 in the mornings.
There will always be a small voltage drop on a circuit like this as opposed to direct battery connection due to other circuits are consuming current.

Modern cars are absurdly sensitive to voltage. I see 11.8V on my 'jeep' with a 2 year old battery before starting and straight to 14V on its voltmeter (and the ciggy lighter plug in jobby - well handy!) on start up and no problems. 0.3V lower (max) and your Jeep is throwing wobblies.
Is there a reason the electronics cant be made to function at a slightly lower Voltage (other than the ensuing over-Voltage with engine running frying them)?
 
Some modern sealed batteries don't provide access to check the specific gravity of the electrolyte so rested voltage is the only way to check state of charge. Rested means at least several hours after the engine was last run or charged and with the car asleep so that it pulling negligible current. Modern cars don't make this particularly by waking up every time you open a door. The best way to do this is establish a benchmark when the battery is new for example I have an GEL/AGM hybrid battery which measured 13.05 volts when new which is a fair bit higher than typical even for AGMs. Even at 5 years old it still manages 12.95 volts. It's getting so there is no fixed voltage you can read out of a book and say that's what a particular battery type should be.
 
I found this image on Google - is it accurate in terms of being a rough guide to how much battery your car has left, based on a volt meter reading?

main-qimg-aac5d9eb61271f2469b5b2065520f846.webp
 
It's correct for a normal non AGM battery but kind of makes my point by being a couple of tenths low for a typical AGM.
 
I just use my multimeter
Not everyone can use a multi meter, some have no idea what they are and most would never pay what a good multi meter costs if they do not need it for work.

My Fluke and Megger equipment are mine for work, this £2.99 thing is all most people will ever need. I would also be happy to lend it out to a mate...my 'proper' test equipment ? Never.
 
Don't throw batteries away!

Go and weigh them in at your nearest scrap merchants, I got a tenner for my last one. They are full of lead.
 
^^^ Agreed , I have weighed in all sorts of stuff, but one battery is not worth most peoples time and effort. By the time you have registered your bank details with the scrap merchant for payment and been issued with a 'membership' card it can be too much hassle .

Just the other day i did a 'tip run' in my van (leaving me with 8 more authorised visits before I have to apply for a new permit) . On board I had the old (big) battery from my C55 and an alarm system battery, It was not worth my time and fuel to divert to the scrap dealer that I have an account with, the batteries went to the recycling centre.

It is illegal for a scrap merchant to pay you in cash - there are some (rare) exemptions - so if you are uncomfortable with a scrap merchant having your bank details it's off to the local dump for you.

P.S some dealers have you drive on to a weigh bridge then into the yard , so If you have tyres that you would rather not see rolling over stray bit's of metal , stay away !
 

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