RDX_jex

Hi,

I need a friend with an RDX so I can measure their car battery after the electrical system is fully on

For now I will skip the whole story other than saying a mechanic told me one thing is NOT normal, then after they made a repair, they told me suddenly - Oh that is normal behavior; and thus the part replacement was pointless.

Could someone with a RDX gen 1, check if their car can support the car's electrical load when all the electrical is turned on and the car is left to idle (approx 800 RPM).

Turn on your: 1. head lights high beam, 2. front defog button, 3. rear defrost button, 4. heated seats.
then measure he voltage over the battery from the alternator and watch the voltage for a little while and see if it slowly drops down (i.e. the battery is discharging).

Does your battery drop to for example drop to 12.3 and lower?
Mine goes from charing say 13.8 to 12.8 and continues to drop down. I also measured that the current coming from the battery and the battery is NOW supply 14 Amp to the car instead of charging.
So if left in this state the battery just continues to get drained down.
The dealer said that this is normal behavior.
Is it really ?

Is that what happens on your RDX? If you don't have a current meter you can check with a multimeter and confirm the voltage goes from charging e.g. 13.8V etc with no load, down to around 12.6V and the voltage will just continue to drop down from there as you watch it with all your electrical system turned on as above.

Thanks for any help

Tomtwtwtw

Our alternators are rated at 110 amps if I recall right, and at idle speed you're getting maybe half of that. Now factor in the electrical systems that keep the engine running, plus headlights, heated seats and defrosters (those especially take a lot of amps), and yes you're most likely going to be drawing more power than the alternator can supply, so the battery will drain.

But in a typical real life scenario you'll be actually driving, so at 2000+ rpm the alternator should be able to cover the electrical demand. Plus rarely will you use all of those things at once for an extended period of time.

RDX_jex

I'm not sure I agree with it not happening much.
If you stop at the stop light, or stop to wait for someone, wait for your kids in car, its quite likely that you could have your lights, defrost, and defog on - and your car is drawing 10A FROM the battery.
Perhaps this is why on new vehicles batteries are not lasting like they used to.
I'm just surprised the vehicle can be left in a condition that if you turned on those items and left it running idle, it would drain your battery right down.

Tomtwtwtw

I mean extended periods of time. It will take much more than a few minutes at a stop light to drain a healthy battery. Point being, it's normal for accessories to draw more than the alternator can provide at idle.

RDX_jex

Hi

I am not saynig just at lights - I am saying if I turn on those 3 tiems and left it idling it would draing the battery.
How long can a battyer sit there supplying 20A to the car and remain healthy?

I need someone to test their RDX, because it does not sound like this should be happening.

See this:
Honda alternator and charging systems explained — Ricks Free Auto Repair Advice Ricks Free Auto Repair Advice | Automotive Repair Tips and How-To

He explains that these cars should be sensing this condition and causing the car to adjust the alternator to go into full field mode and provide the full alternator output to support the electrical loads. In high mode (even at idle) it should be switching on to charge the electrical load needed.

A friend checked his Subara - and with FULL electrical load the thing keeps the voltage at 14.x volts supplying all current to the car that it needs (i.e. not like what I am seeing where the votlage drops into 12.3V and even lower becuase the battery starts to have to supply 20A of current to make up for the load.)

Tomtwtwtw

You can't create power when power doesn't exist. Your friend's Subie may have a higher output alternator and/or less electrical demand from its accessories. But on an RDX, full electric load will demand more than an alternator can provide at idle speed. It spins at a fixed ratio to engine speed. If you want more power at idle, you can install a smaller pulley on your alternator so that it spins faster, but that can wear it out faster, and if you go too small you may not have enough tension on your accessory belt.

Here is a study showing typical alternator output in relation to engine speed. They load up accessories and measure voltage drops after 5 minutes at idle, 1500 rpm and 3000 rpm, and the voltage drop is more pronounced at lower engine speeds (where alternator is not producing as much current).

https://www.matec-conferences.org/ar...2017_01076.pdf

"When the engine is running, the alternator supplies electricity which, depending on the voltage level in the vehicle electrical system (determined by the alternator speed and the consumers drawing current), is normally enough to power the consumers and charge the battery as well. If the equipment current draw in the vehicle electrical system is greater than the alternator current (when engine is idling), the battery is discharged. The vehicle system voltage falls to the voltage level of the battery from which current is drawn. If the equipment current draw is less than the alternator current output, a proportion of the current flows to the battery and acts as a battery charging current."

RDX_jex

Hi

I'm not creating power that doens't exist.
There is 75 Amps coming from the alternator, it should be able to give 110A.
At idle I only have to slightly rev the engine so I can barely see the rpm gauge move, we are talking like seeing 850 rpm at idle and then seeing it barly move to who knows 890 rpm and it is now providing the current.

See the link I provide. Even at idle the new charging systems from accura are supposed to be able to supply the current by switching the full field on the alternator on.
What you are describing is OLD fashined alternator that doesn't have this adjustable alternator system from Acura.
Acura has created modes on the alternator so that it can provide more current or less current depending on what it is told by the computer.
See the link i sent.

We need to measure this on another RDX for proof to know if other RDX do the same thing or not.

"

Honda alternator high output mode

The ELD reports to the ECM and the ECM, along with various other sensors determines the charging voltage. For example, if the ECM detects an AC request and powers the AC compressor clutch, the ECM will set the charging rate at 14.4-14.9V. This is referred to as the high output mode

Outside of the above listed low output mode parameters, the ECM will place the charging system in the high output mode.

...

"

Tomtwtwtw

I think you are confusing voltage states with actual current delivery, and even if the electrical system flips to high voltage, once the total current demand of the system exceeds supply from the alternator, the voltage in the system will start to drop. As I've been saying, you're not ever going to see the full 110 amps at idle. The alternator cannot provide full power when it's spinning too slow, and will not maintain the full charging voltage if the electrical demand is too high. If you turned off some accessories, then you should expect the system to run in high voltage until the battery is charged, and then step back down to maintain the battery (effectively becoming a trickle charger so as not to prematurely wear out the battery).

Have you tried doing your same test, but holding the rpm around 2000? If so do you still see low voltage, or is above 14? I would expect above 14, because at 2000 rpm+ your alternator should be able to deliver its full rated amperage, which in turn should be enough to power all your accessories *and* charge your battery.

Bottom line, I agree with your dealer (and pretty much every other source I can see out there) that it is normal for a battery to enter discharge state when a vehicle is idling and you are powering every possible electrical component you can. It seems like you're bound and determined to find a problem where one doesn't seem to exist. Hopefully someone else can do some measurements and give you some peace of mind.

Chopperpilot

I just tested the charging system on my 08 RDX this afternoon out of curiosity with a multi meter. Battery voltage cold 12.5 .
Voltage during fast idle ,no accessories on spiking @ 14.5 .
Now with headlamps full blast , blower motor , defrosters ,seats and AC it’s anywhere between 14.1 -14.4 volts at idle .
I was kinda amazed when the AC clutch would cycle in and out , voltage dropped below 13.0 for a second once it engaged but returned to the 14s instantly.

Hope this helps ..you might just need an alternator in the future.

RDX_jex

GREAT ! EXACTLY! Thank you for doing this!!!! This is what I have read should be happening at idle !!
the dealer even said this FIRST that the car should be able to handle those electrical items turned on at idle, and then only after they replaced NEW alternator with another NEW alternator (which did NOT fix the issue) then suddenly they claimed oh, its normal behavior that at idle the car can't supply all the current. (AND it has a new battery too!).

So your CAR at idle DOES supply all the current (and stay in the 14V range). Wow - so that shows this is how it should be operating.
Now.... how to trouble shoot this... ????

Sevitrey

My MDX had this same problem when I replaced the alternator with an O'Reilys brand instead of OEM. You might just need a better/OEM alternator.

RDX_jex

Hi,
I used both the NEW Acura alternator, as well as a Denso - and they BOTH did it...

DaIll1

The HFL (hands free link) module is well known for causing a lot of electrical system anomalies. After much trouble with mine I had it disconnected and have had no problems since.

RDX_jex

Yeah, HFL isn't the issue here. That was checked, but also the issue the HFL is known for is drawing too much current when the vehicle is off and thus draining the battery.I don't see that issue.
This issue I see is when the car is running at idle as described in my first post. For some reason it doesn't supply enough current with all the listed systems on, but with a tiny bit if rpm it does; however, I have been through 2 new alternators and the same thing happens etc.
Dealership first said it was a problem - but afterwards when that didn't fix it they claimed its normal - (makes no sense that it can be 'normal', as per the other guy who posted here and his system at warm idle can support the current load not drawing from the battery).
One mechanic at dealership said he would replace the car's computer next, but he was also claiming it wasn't a problem now... (This is along the lines of the computer is what tells the alternator how much to generate as apparently the acura alternator is able to adjust how much current it supplies).