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Excuse my ignorance but I am completely non technical.

After 10 days of lockdown I couldn't start my tow car and had to jump start it.  I then monitored the battery every few days with a multimeter across the battery terminals and started the engine if felt necessary.  To save opening the bonnet and removing the battery cover every time I purchased a tester that used the 12V sockets in the car and started getting worried about the condition of the battery.  So yesterday I used the multimeter and the 12V socket meter.  The multimeter showed 12.39V and the 12V internal socket showed 11.6V.  Have I just bought a dodgy meter or is there a reason that the sockets run at a lower voltage than the battery direct ?

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When you are measuring the voltage at the socket it has struggled through the car's wiring and fuse box. You may also find that when you open the car cars, stiff in the car get activated and powered up (interior light, dashboards etc) all this stuff will take power from the battery, not a lot but it will reduce the voltage that you measure.

 

The correct place to measure your battery voltage is directly across the battery as anywhere else will give inaccurate results.

 

BTW 12.39 volts is low - about 60% charged so you need to recharge it. The voltage when the babbery is fully charged but sitting idle should be around 12.6 to 12,7.  Taking the car for a run wont charge it properly, it needs to be put on charge with a decent charger for about 24 hours

 

A trawl through this should help you understand what is going on - 

 

Edited by matelodave
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1 hour ago, matelodave said:

When you are measuring the voltage at the socket it has struggled through the car's wiring and fuse box. You may also find that when you open the car cars, stiff in the car get activated and powered up (interior light, dashboards etc) all this stuff will take power from the battery, not a lot but it will reduce the voltage that you measure.

 

The correct place to measure your battery voltage is directly across the battery as anywhere else will give inaccurate results.

 

BTW 12.39 volts is low - about 60% charged so you need to recharge it. The voltage when the babbery is fully charged but sitting idle should be around 12.6 to 12,7.  Taking the car for a run wont charge it properly, it needs to be put on charge with a decent charger for about 24 hours

 

Thanks for the input.

Battery was 12.7 after 24 hours charge, 12.5 - 2 hrs later and 12.2 the next morning.

New battery on order!

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7 minutes ago, bubble2015 said:

Thanks for the input.

Battery was 12.7 after 24 hours charge, 12.5 - 2 hrs later and 12.2 the next morning.

New battery on order!

 

Possibly, but you may have a high parasitic drain on the battery, ideally have the battery tested by a reliable garage, some only want to sell a battery even if yours is good !

 

The following presumes you charged the battery on the vehicle, by the way, how old is the battery, approx.

 

A quick test, if you are not too up on electrics, would be do the same as you have done above, charge for 24 hrs but with the battery disconnected, ( no need to remove it from the vehicle just disconnect and tuck the - lead away) and test as you did again, if it now stays within the parameters that Dave suggests, it is possibly OK, if not then it appears to be failing.

 

Warning, before disconnecting, check your vehicle handbook ref radio codes, alarm and central locking etc and also the sequence for disconnecting and reconnecting the battery, it isn't as simple on some vehicles as it used to be.

 

If it stays OK then there is obviously something consuming the current on the car which can be found with an Amps draw test, most multimeters will do this, baring in mind that all modern vehicles there is a constant Amp draw, milliamps actually,  from such as alarm, radio, clock etc. and not forgetting that any battery self discharges over time, both these discharges should however be minimal.

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Thanks for the comments.  I have a CTEK charger so is it safe to connect this to the battery without disconnecting the battery from the car ?  Should the negative lead go on the negative terminal or a suitable earth point ?  Many thanks.

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I have not found my CTEK chargers have ever caused issues with any car's electronics I have owned, and I leave our Disco 4 for example on it most of the winter 24 x 7 .

 

Best always avoid going directly onto the battery posts [clearly if possible] as any possible spark will be at the battery itself where explosive gases "might" be present.

Connect positive first onto the battery, then connect negative on a body part away from the battery, or ideally a provided "grounding" point. Uncouple in exactly the reverse order, break the circuit first by uncoupling the negative, away from the battery, again so no local sparks.

 

Edit: leaving your battery as low as 12.4 volts is doing it no favours at all, even more so if already owning one of the very good CTEK chargers!

Unlike some technology batteries out Lead Acid batteries should always be left as close to 100% full as practical. Your CTEK knows this and if left on will do that.

 

 

Edited by JTQ
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20 minutes ago, bigbilly said:

Thanks for the comments.  I have a CTEK charger so is it safe to connect this to the battery without disconnecting the battery from the car ?  Should the negative lead go on the negative terminal or a suitable earth point ?  Many thanks.

In general yes if the battery is in reasonable condition but read your charger and car manuals. My CTEK charger has several settings for different batteries and uses. For example AGM battery, conventional flooded Pb, reconditioning, and PSU. I would suggest that it isn't safe to use the reconditioning setting as that uses high voltage pulses that may damage sensitive electronics in the car.

 

Usually safer to connect the positive terminal first then the negative to a chassis point away from the battery. Disconnect in reverse order. This is simply to reduce the chance of igniting hydrogen gassing from the battery when connecting/disconnecting a terminal.

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1 minute ago, JTQ said:

I have not found my CTEK chargers have ever caused issues with any car's electronics I have owned, and I leave our Disco 4 for example on it most of the winter 24 x 7 .

 

Best always avoid going directly onto the battery posts [clearly if possible] as any possible spark will be at the battery itself where explosive gases "might" be present.

Connect positive first onto the battery, then connect negative on a body part away from the battery, or ideally a provided "grounding" point. Uncouple in exactly the reverse order, break the circuit first by uncoupling the negative, away from the battery, again so no local sparks.

 

The order should be, with charger switched off / unplugged, connect charger then switch on/ plug in, when removing the charger, switch off / unplug charger then dis-connect, this way there is no chance of any sparks being produced.

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11 minutes ago, Silversurf said:

 

The order should be, with charger switched off / unplugged, connect charger then switch on/ plug in, when removing the charger, switch off / unplug charger then dis-connect, this way there is no chance of any sparks being produced.

 

Switched off of course, but even if off, there will always be some drain that the charger will take, not all inflicting just a few mV  in steady state as a CTEK, but all best practice avoiding.

So there is still going to be a spark at the battery any which way, if the final connection is made at the posts.

Igniting a hydrogen air mix requires just 0.02 millijoules, that is 10% of that required to flash off petrol vapour!

 

 

Edited by JTQ
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I've been using a plug in voltmeter since 2013 and always found the voltages to be the same as measuring across the battery direct.

I've also checked them for accuracy against a professional voltmeter and found the accuracy to be with in 0.1 volts +/-

 

As already mentioned you only get a true battery reading across the battery after all the car systems have shut down, so i always allow 30 mins for this.

 

During shut down I've topped my battery up twice now using a Aldi smart charger, but i always connect the battery then switch mains on, so no connecting to a discharged battery using live clamps.

 

Also these stop start batteries do not in my experience retain the same voltage levels as say a caravan battery, so its no surprise to me to see voltages below 12.6 volts before start up.

 

 

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1 hour ago, bigbilly said:

Thanks for the comments.  I have a CTEK charger so is it safe to connect this to the battery without disconnecting the battery from the car ?  Should the negative lead go on the negative terminal or a suitable earth point ?  Many thanks.

Normally I'd say to the battery terminals but I have to use the earth terminal on the car because the battery terminal is inaccessible. Some cars do have tabs where battery chargers or jump leads should be connected. Check your handbook but generally you dont have to disconnect the battery from the car when using charger's but follow the precautions outlined above

 

My handbook says to disconnect the battery if the car is to be left for a long period, presumably because of all the parasitic drains from the alarm and other stuff. 

Edited by matelodave
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1 hour ago, JTQ said:

 

Switched off of course, but even if off, there will always be some drain that the charger will take, not all inflicting just a few mV  in steady state as a CTEK, but all best practice avoiding.

So there is still going to be a spark at the battery any which way, if the final connection is made at the posts.

Igniting a hydrogen air mix requires just 0.02 millijoules, that is 10% of that required to flash off petrol vapour!

 

 

 

Interesting point you raise JT, though I think you mean mA and something I hadn't thought of, a discharge when switched off.

 

However, being the nosey ' b ' that I am I thought a little experiment is the order of the day whilst I'm waiting for some epoxy primer to flash off.

 

I can't at the moment try with my Ctek 10, a neighbour down in the village borrowed it yesterday, so I did a quick test with my Optimate I use for motorbikes, similar smart charger with similar stages but the max. output is about 1A  for the smaller batteries, I think the results will be similar, confirmed when the Ctek makes its way back up the hill.

 

So, the Optimate, not plugged in consumes 0.097A or 9.7 μA a tiny amount, but not insignificant over time, but sufficient to create an arc of any consequence ?, though any arc is dodgy where there are gases that like to go bang at the slightest excuse,  oxy and hydrogen being the best. 😱

 

I'll update when the Ctek returns.

 

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Pedantic but 0.097A is actually 97mA and there are 1000 micrAmps to a milli amp. 

Graham

Unless otherwise stated all posts are my personal opinion 

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1 hour ago, Silversurf said:

 

Interesting point you raise JT, though I think you mean mA and something I hadn't thought of, a discharge when switched off.

 

However, being the nosey ' b ' that I am I thought a little experiment is the order of the day whilst I'm waiting for some epoxy primer to flash off.

 

I can't at the moment try with my Ctek 10, a neighbour down in the village borrowed it yesterday, so I did a quick test with my Optimate I use for motorbikes, similar smart charger with similar stages but the max. output is about 1A  for the smaller batteries, I think the results will be similar, confirmed when the Ctek makes its way back up the hill.

 

So, the Optimate, not plugged in consumes 0.097A or 9.7 μA a tiny amount, but not insignificant over time, but sufficient to create an arc of any consequence ?, though any arc is dodgy where there are gases that like to go bang at the slightest excuse,  oxy and hydrogen being the best. 😱

 

I'll update when the Ctek returns.

 

 

Indeed, I did intend to type mA, brain way in front of my single finger typing, sorry.

 

The CTEK MXS 10 similar to my MXS 5 has a published drain of sub 1Ah per Month, [<1.34mA] but that is a mean steady state value not the all important instantaneous surge associated with connections/disconnections. Finding that spark energy figure is going to be away more challenging, well beyond my pay scale. LINK

 

Basically the general point I was trying to make is that even with the better chargers with inherently low self draining surges, "best practice" is not to make the final connection on the battery itself, hydrogen is incredibly easy to ignite.

 

 

 

Edited by JTQ
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My Bro can tell you all about that.

 

He had a battery explode in his face as a result of disconnecting a charger whilst it was switched on. The car was in a workshop with the bonnet open - suffice it to say he ended up in A&E having his eyes and upper body irrigated for a very prolonged period and then suffering with a sore face, eyes and arms for several days afterwards (his clothing had to be whipped off pretty quickly - fortunately his workmates were savvy enough to take him straight outside and hose him down. - He was lucky that he wasn't injured by flying battery casing. 

 

Guess who's a lot more careful nowadays

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3 hours ago, WispMan said:

Pedantic but 0.097A is actually 97mA and there are 1000 micrAmps to a milli amp. 

:Thankyou:

 

I've been happily juggling too many balls today, most have landed now, I just did things quickly earlier, showing what to expect, so have been out to double check.

 

Clue number one, a little battery logo winking at me, yes a new one is now fitted. 👍

Clue number two put the probe leads in the correct sockets, 🙄😊I know!

 

With everything correct, here are the new readings from the Optimate:

 

Using 10A input:

 

0.12 μA

0.02 mA

0.002 A

 

Using μA / mA input:

 

258.8 μA

0.24mA

0.002 A

 

I have however been successful with my other tasks today, Zapcat engine, ally weld bottom end, repaired and now in primer, Helicoiled a plug hole for a young lad in the village who likes tinkering with minimal tools, welded fractures on a neighbours stump grinder deck, cleaned the bits of a Honda GX390 engine ready for re-build, vac and pressure tested a Zama carb and found an elusive fault, had a good tool tidy up, nipped to my favourite market ( about 10 miles from home ) for oven bottom muffins, baguettes, fresh fish salmon and haddock, fresh meat pork, lamb and beef and fresh fruit, got to keep the local small shops going, lopped off some rhubarb from my garden and dug up almost the last beetroot, dug some up some early new potatoes, pulled a nice Lollo Rosa lettuce, sowed some Mediterranean lettuce seeds for use as micro or baby leaves.

 

All that remains now is to do a rhubarb crumble and rhubarb pie, decide which fish to have, wash and cook  some of the potatoes, boil an egg, both to cool off for my salad, dig the rest of the salad bits out of the fridge and decide which wine I'm going to sit outside with, after a walk to the top of the hill, watching the sun go down.

 

I dropped a clanger with the meter readings, you can be certain I won't drop a clanger with the food and drink though. 😋🍷😂😉

 

 

 

 

 

 

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