fluctuating voltage on a 2010 montero

**altec** · September 16th, 2012 10:47 AM

I got a 2010 montero foreclosed from a bank. Patay na ang battery kaya pinalitan ko. After a month of use, I noticed when the idling rpm is at 650 and when revving or when the rpm goes up to 850 when the compressor switches on, lumalakas ang headlight, blower, pati ang dome light sa loob at humihina pag nasa 650rpm. Pinatingin ko sa mitsu casa who connected the battery to a computer/digital battery tester. Wala daw problema ang charging at yung battery. Readings come to high 13 (13.8 or so) to 14. Ginawa na nila ito 6x na. The problem became more of a concern kasi on a few occasions, yung stereo headunit would reboot or trip off and switch back on when I press something: volume, change fm station. Pinatingin ko to several accessory stores and the battery shop where I bought the battery. Using their testers, we noticed the voltage would stay at the 14 level when the rev is high or none of the electrical loads are switched on. Pag binuksan ang headlight (on high beam), fog lights, stereo, (aircon blower without switching on the compressor to avoid the rpm from going up) eto na, slowly bumaba ang volt. I took a picture of the digital voltmeter registering 12.79 after several minutes of watching it go down. Naka timing naman ako may pumasok na 2012 glx montero sa accessory shop. The owner allowed me to check his ride's voltage and switching on the same electrical load, 13.9 yung kanya. Pinakita ko sa service manager ng mitsu casa yung pictures ng voltage readings. But still after 2 days of testing, sabi pa rin niya normal lang daw ito kasi they checked with 5 other monteros in the shop, nagfi-flicker talaga ang headlights ng montero but not on the Stradas.

Sabi ko sa kanya, di yan normal kasi pag na timing ka sa traffic at di naman naka on ang compressor mo sa gabi and the effect is lower rpm, dahan dahan mauubos ang battery ko. But because THEIR computer battery tester said its normal (yung may print out), they cannot make any repairs or warranty claims. I want them to open up the alternator coz 2 other shops (hindi na yung accessory shops na sinabi ko) told me nasa alternator ang problema.

Does anyone have any experience like this or any suggestions? The montero still has around 10 months under warranty to go. 20K mileage, 2010 GLS 4x2 A/T model. Kung hindi pwede iclaim sa warranty o hindi pwede ipaayos sa casa dahil nga sabi nila normal lang yan, ipatrabaho ko na lang kaya sa labas?

Yung accessory shops pala, refuse to install accessories sa montero (wanted to improve the sound system and horn upgrade) kasi nga bumababa ang voltage.

**akosijepoii** · September 16th, 2012 06:34 PM

kung alternator prob nyan sir try mu contakin 7824668 kayang kaya yan...

**Retz** · September 16th, 2012 06:51 PM

Pa check-up mo muna sa Casa kung under warranty pa.

**miko101130** · September 16th, 2012 07:37 PM

I'll try to help you sir...
Dapat pag naka idle ka at walang load ang vehicle, usually 13.5-14.5 ang voltage at the battery...

The minimum voltage at idle speed should be 12.5 volts at the battery... This means that the battery is not discharging and also not charging...
Any drop below this voltage at idle with no load is attributed to alternator problem..

The capacity of your alternator, found on the alternator on a sticker, will determine how many AMPERES it can produce..

Example, an alternator rated at 90 amps, with a 13 nominal voltage will produce 1170 watts.... If your total electrical load reaches more than 1170 watts, then the alternator cannot charge the battery even at full capacity simply because the demand is higher than what can be supplied...

The alternator in your car is designed to provide electricity and still be able to charge the battery even if all your "stock electrical accesories are open"....

If the alternator will drop its voltage even without much load, probably at 50% load only, then the alternator or the PCM is at fault!
That is if the battery are 100% ok and grounding is ok..

Usually the charging inside the alternator is ruled by the diodes, 6 of them, 3 pairs... Then the voltage is controlled by a voltage regulator built inside, so that voltage will not increase above 14 or more even at full speed...

On newly built vehicles, the PCM, powertrain control module, also has the function of controlling the charging of the vehicle...

If the pcm is ok, then it will most likely be the alternator, assuming that the battery is ok and no other electrical issues at hand..

I'll give another example,
On my vehicle, my alternator is rated at 75 amps... Therfore at full capacity my alternator can produce 975 watts if the system demands it... At idle my alternator probably produces 20- 40 amps... Suffecient for normal use with vehicle accesories.
Aircon,headlights,engine...

At idle my voltage reading via a digital volt meter at the battery terminal is at 13.9 volts...
Every electrical load you switch on will lessen that 13.9 volts.

Headlight = 10 amps
Aircon= 10amps
Brake lights=5 amps
Parklight= 5 amps
Stock sounds= 10amps
Abs/ecu/ etc= 20 amps

Total is 60 amps... So there is still a 15 amp reserve still available for other accesories...
Total is 780watts... There is still 195 watts reserve capacity...

My voltage reading at this point will be at 13.1 to 13.2 volts...

If i use my auxilliary lights which consumes 400 watts
I will be at 12.3 volts.. So im discharging... Because im over the capacity ans the battery is supplying the extra power the accesories will use hence it will drop its voltage...

**miked** · September 16th, 2012 09:14 PM

isa pa, ano ang mga previous PMS na ginawa sa sasakyan nyo po bago nangyari ito? kasi baka simpleng maluwag na serpentine belt or some other simple things na hindi masyado napapansin. start with the basics first ika nga.

**miko101130** · September 16th, 2012 10:05 PM

one things pala TS... according to your statement, the same electrical load was applied on a similar montero that was also there at the time you are at the accessory shop... your reading with your montero at load is 12.7, while the other montero reads at 13.7... granting everything else equal among your units....

if the vehicle is still under warranty, try to pursue that path...
vehicle headlights should not flicker.... kasi pag nag flicker it signals that there was voltage drop that occured in the electrical line...
pero before you go and isolate the problem on the alternator, be sure that the battery, battery terminals, grounding, are all ok...

try to put the vehicle in high beam and see if the dome lights will dim... or if the gauges will dim/blink then return to normal...

**miked** · September 16th, 2012 09:09 PM

Originally Posted by altec

Pag binuksan ang headlight (on high beam), fog lights, stereo, (aircon blower without switching on the compressor to avoid the rpm from going up) eto na, slowly bumaba ang volt.

bakit mo iaavoid yung idle up? kaya may idle up para mamaintain yung desired output ng alternator esp. kung A/C na ang nakaandar. pinakamalakas humigop ng current and AC (provided no boom boom sounds and powerful lights)

**miko101130** · September 17th, 2012 10:35 PM

Yep... Kakatawa naman yung SA... Pinipilit niya talaga yung baluktot niyang paniniwala at reasoning...12.7 volts is not normal with standard oem load..
If me technical manual sila, meron yang factory spec of what the alternator readings should be.... Analog tester or digital tester are fairly accurate..

Hahaha... Galing talaga ng s.a,, pag papa warranty client dame dahilan,,,
Onga sir, pull out mo muna habang wala pa service alternator,, baka ma-hocus pocus yan.. Hihihi...

**light2light** · September 20th, 2012 05:24 PM

sa battery charging, mas accurate kung alam mo ang charging current. may voltage reading ka na, dapat may ammeter ka pa.
i dont know why most cars do not have ammeters. basing your readings on both voltage and current is the surest way to analyse
battery problems. 3 cents worth lang po.

**miked** · September 21st, 2012 11:50 AM

the starter motor is the greatest power consuming device on a car. say a 2 hp starter motor will draw about 120-200 amperes. common automotive ammeters have usually a maximum reading of 100 A. usual gage have 60 A. thus the gage will blow out. afaik, ampere gages used on cars have a wire wired in parallel to the ampere gage to prevent this. exception are the alternator and starter testers used by auto and battery shops.

so my say is the voltmeter is better than the ammeter to check for a no-charge or overcharging condition. ammeters are way cheaper than voltmeters thats why most mechanics around the block use it for cars