December 2010 Mazda2 TS2 1.35litre (Mazda2 is called Demio in some other countries). Series DE.

It has problem with low battery charging voltage which i think is caused by battery monitor (it has one on the negative battery terminal like Fords). Voltage does go up to about 14 volts when disconnecting the two thin wires on the battery monitor but that makes dash battery light come on.

I think it needs the monitor resetting as I changed the battery. I can't find anywhere using google that tells me how and got no replies to this on Mazda forum. Whilst Forscan lite (on iphone) does work on this Mazda using ELM327 Tunnelrat OBD device there does not seem to be anything on there relating to battery monitor. 

The ford method of resetting (ignition on, flash main beam 5 times, press brake pedal three times, then battery light flashes) does not seem to work.

Someone somewhere must know how it's done (I won't be taking it to Mazda garage and asking them to do it due to cost).

I know it's a long shot putting the questions on here. By some miracle does any one on here know?

(this link to message on mazda forum gives more detail: https://www.mazdaforum.com/forum/mazda2-53/charging-problem-2010-mazda2-de-1-35litre-50831/

 

Your Mazda uses the same charging system as most Ford's.

What happens when you disconnect the smart charge monitor plug on the alternator ?

Does the voltage at the battery terminals rise to around 13.9V

There is no real need to reset the battery monitor system unless you have installed a brand new battery. The battery monitor in the negative lead will reset itself after 2 or 3 days of normal driving (it won't of course reset the 'days elapsed' counter).

I think your real problem is that battery CCA is too small even if the Ah size is correct.

Cold cranking amps (CCA) - CCA is critical for good cranking ability. It's the number of amps a battery can support for 30 seconds at a temperature of -18C until the battery voltage drops to unusable levels.

If I disconnect the plug on the alternator there is no output at all from the alternator. I thought that would make it default to about 14 volts but it does not. The plug socket on the alternator has three small flat blade connectors in it. the plug itself only has two connectors/two wires. From examining the plug that is definitely how it was made, there is not a broken terminal/wire.  The alternator says FoMoCo on it but I assume it is wired differently to ones used on Ford cars. I did instal a new battery.  During 7 year ownership I have replaced battery twice and I have for a long time felt the speed of starter motor sounded like battery charge was low.  More about voltage readings on the mazda forum via link in first post.  It's so annoying how complicated all this stuff is these days.  you knew where you were with a Cortina (although rust and reliability were worse I admit)

Yes I've read the Mazda forum messages on the subject.

It is very normal that the alternator smart charge plug is a 3 pin type with only 2 wires. Some Ford's do use all 3 pins but most only use 2.

Disconnecting the alternator smart charge plug should switch the charging from the alternator in to it's emergency default charge mode and voltage measured at the battery terminals would then be around 13.9V

You say when you disconnect the smart plug you have no output from the alternator. How are you measuring that ?

i was measuring it with a voltmeter on the battery terminals   and    also trying the voltmeter from the main big output terminal on the alternator with the other probe on the alternator casing, making sure it was getting through to clean metal.  Both ways, with engine running, idling and revving, it was just showing the same reading as if the engine was not running, 11 point something volts. So perhaps there is a fault in the alternator if that does not make it default to something like 14 volts. Almost certainly original alternator. Car only done 55k miles but I know mileage isn't a good measure of wear and tear. and anything electrical can just go wrong at any time in its life. 

Hi Isetta the only 100% way to measure what is current coming out of the alternator is, to install a current meter in the main alternator cable or an easier option would be to use a current clamp meter.

I've read back through all your battery voltage measurements and to be honest they are about, and are acting, pretty as I'd expect them to. With the exception of disconnecting the alternator smart plug which should cause the charging system to run in default mode.

Your slow starting motor cranking speed is quite possibly due to the battery CCA just been too small for your car. Do you know what the original specification was compared to the battery you have now ?

well to be honest the current battery is lower AH and lower CCA and physically smaller than the original as I'm a cheapskate.

the battery is 40AH and 340CCA size 063 from eurocarparts, Lion brand.  I think the original would be something like 50AH 400CCA as far as I can tell from looking it up.  My theory is that makers have to spec the battery for worse case scenario for the country the car is sold in. Living in the south of England and not in the Scottish highlands I figure I can go lower spec as climate not as severe down here.   I know readers of this will be laughing at me .   It's the voltage readings that were making me think there is something else wrong.   But the car does always start so I'll keep my fingers crossed. My wife only drives it locally so it's not like she'll be stuck 50 miles away. fingers crossed it will not turn into a real problem.

3 hours ago, isetta said:

the battery is 40AH and 340CCA size 063 from eurocarparts, Lion brand.

Yes I would say your battery is a bit under the min spec. Below is the Mazda factory specifications.