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Crazy phantom battery drain ?

Hi again,
Checked the battery voltage again this morning. The car went on a 2 mile run yesterday with 3 stop/starts and idled while it warmed up for me to check the alternator output.
Battery reading this morning 12.62v. Thats a drop of only 0.02 volts in 24 hours. That looks better.
Yesterday I pulled all the fuses and found the drains as stated earlier.
Something happened today that I hadn't noticed before.
Took the car out and drove a 20 mile round trip.
The digital voltmeter generally read 14.2 to 14.4 volts. However a couple of times it dropped to 12.8 v for maybe 20 seconds.
When I got home and was parking up it was showing 12.6 v on idle. Never seen this before as the alternator voltage was always in play.
Got the multimeter on the battery and it read 12.6 volts on idle, put the headlights on and the volts went to 14.1.
Lights off, rev to 2000 12.6 volts, lift off throttle volts increase to 14.1 and then drop back to 12.6.
I checked all the fuses are in place.
Given that 12.6 volts at the battery should mean fully charged, would it be that the alternator is stopping charging until the battery drops below 12.6 ?
This may well be the way the charging system should work and I may have disturbed something during my search for the drain, but if this isn't as it should be, is there a charging relay on the car ?
 
Just had a look at alernators and they have a clutch/pulley ? Why and how does that work, I have noticed a whine for the first 10 minitues or so after starting.
 
I've never had any problems with the alternator on my car, which is the 2.4 petrol ...so I don't know much about the alternators on the Accord

But, the issue does come up fairly often on the diesel, and the alternator pulley has a mechanical clutch which allows it to freewheel on the overrun, for some reason.

That might be the cause of the problem, although what you have observed could be normal charging behaviour.

Charging circuit diagram below (it's in two parts, click on each part to get a bigger view)
Note: this is the petrol, diesel is very similar, but some connections/wire-colours will be different


SEA3E00A14100000000EAAT00_1.jpg

SEA3E00A14100000000EAAT00_2.jpg
 
Good diagrams. Looks like the "ELD" unit controls charge. I have no idea where that is.
I think that the voltage sensors for the charging must see the battery at 12.6v as "full". Because as soon as I put the sidelights on - causing a fractional voltage drop on the battery - the alternator kicked in.
Just ticking over wouldn't use power as on a petrol engine.
Wonder if I've reset something that was stuck by pulling all the fuses ?
Maybe this is how it's always supposed to work.
How this relates to the battery going down I don't know, unless the alternator was cooking it.
Just checked battery after 4 hours standing and its still at 12.6v.
 
geoffdragon said:
Just ticking over wouldn't use power as on a petrol engine.
Click to expand...
I wouldn't be so sure of that, the fuel pump and injectors on a modern diesel engine would draw as much as the coil(s) on a petrol engine



geoffdragon said:
How this relates to the battery going down I don't know, unless the alternator was cooking it.
Click to expand...

maybe the battery is ok after all ?

Although the charging system met the criteria of the 2000 rpm headlights-on test, intermittent-charging also equals under-charging. On the other hand, maybe constant charging at 14+ volts equals over-charging instead.

Intermittent-charging could lead to a diminished A-h, yet the battery would probably seem ok on a standard load-test device across the terminals. Constant 14+ charging might also boil off some of the water, yet also seem ok on a standard load-test device across the terminals. Most reliable test on a lead-acid battery has to be a hydrometer I reckon.

But yes, there is the possibility that something was wrong and now if it is ok, the car will stand for a few weeks with that 75 Ah battey.

I still think that the 45 Ah battery in the 2.4 petrol is not enough ....I'm looking forward to getting that A-h meter ;)
 
geoffdragon said:
Yes it would be better to test with hydrometer but it's a sealed battery. Damned manufacturers again.
Click to expand...
Car batteries are not sealed, even though they're often called "sealed". if you look you'll see a vent cap on each cell that can usually be removed.

A true sealed lead-acid battery (aka SLA) is the sort of thing you get from Maplins for small devices, also e-bikes often have true SLA, as well as mobility scooters. The only way to get to the acid in a true SLA is with a drill LOL

edit: btw some car batteries have cover(s) that you pull off to reveal the vent-caps.
By "sealed" they mean "maintenance free" i.e. you shouldn't expect to have to top up the cells with distilled water during the lifetime of the battery
 
geoffdragon said:
Btw just put the code reader on the car. Nothing showing. That eld unit throws a dtc if it's faulty.
Click to expand...
Time will tell if the battery is ok ...you'll have to either risk it at the airport, or use the Passat and find out when you get back home from the airport. If it does go flat again, and if the A-h meter shows that the drain is not enough on a 75 Ah battery, then the charging system may have fecked the battery, and as you say, you may have put it right.
 
This thread made me curious so I dug out my multimeter and tried mine.

12.15V across the terminals, 0.23A unlocked, 0.025A locked and powered down.

So yours seems normal.

I left mine 10 days recently and it turned over noticeably slower than usual but still caught first time and has been fine since. And mine is the 45Ah battery. But it shows that 10 days has an impact. 2 or 3 weeks I suspect it wouldn't have started. So it's a characteristic of 7th Gen ownership that we all need to work around.
 
That brilliant. Looks like we have a figure to work to, if anyone else gets a problem. Beefy said a maximum of 30ma but now we have two cars showing 24 - 25 ma. Just need to make sure alternator is keeping battery fully charged now.
 
Regrding my earlier post about the alternator seeming to stop charging with the car idling with no load on the battery.
I came across this post on another forum.
The PDF is not accessible but the operation is explained.

Honda for the most part uses DENSO alternators with internal regulators just like Toyota. However, some Honda vehicles have something called the “ELD” system aka: “Electric Load Detector” I found a PDF that gives everyone some great information : http://bit.ly/10YOHJZ

For many years Honda and Acura have utilized a dual mode charging system to increase fuel efficiency and to decrease the drag on the engine when starting. The two modes can accomplish as much as 10% load reduction on the engine by allowing the Electric Control Module (ECM) to determine charging rates based on information gathered from an Electric Load Detector (ELD) and various other sensors. During heavy electrical or mechanical loads (i.e., if the AC clutch is engaged), the ECM will set the charging voltage to 14.4-14.9V (high output mode); during startup and light electrical load conditions, the ECM will set the charging voltage to 12.4-12.9V (low output mode). In the latter case this anomaly might cause a technician to try to diagnose a low charge problem, although it is normal to have 12.5-12.7 charging voltage when the parameters are met.

This might confuse most technicians because it takes more than 12.6 volts to charge a battery. However, while in the low output mode, the alternator is not actually “charging” the battery but it is just holding the battery voltage at 12.5-12.7 volts. The main draw on the battery occurs during startup and after the battery has been charged there is no need to keep the voltage higher than what the vehicle needs. After the battery has been charged most of the current is drawn from the alternator. Thus, this system increases efficiency by charging the battery only when needed.

Fingers crossed, that's what mine is now doing.
 
Just come back from a 50 mile run and saw voltages I've never seen before on the digital voltmeter. Varying from 14.2 to 14.6 occasionally. Dropping after several miles to 12.6 to 12.9 for short periods. Looks like the smart charging system has come to life. Checked the battery after coming home and it's showing 12.7 volts. Will check again this evening but it looks like the charge system is now working properly. Just need to monitor wether the battery will stand up to a couple of weeks holiday in car park. Been an interesting topic. Thanks to everyone who submitted suggestions and info. Will come back with result.
 
^ continual monitoring of charging volts was an excellent idea Geoff

you might want to send the A-h meter back when it arrives :eek:

(as I mentioned, ebay "But-It-Now" conforms to "distance selling" laws in the UK, so you are allowed to change your mind, you just notify that you want to return it, then you only pay for return postage, best to add on "signed-for" though).
 
Freddo no I'm going to hang onto it. Never know when it may come in handy. It will disappear into my " black hole " workshop. Lol.
Cliffordski that 12.1v sounds like a 50% charged battery. Maybe you should stick a charger on it overnight.
Going to watch amps drop for a few days ( use than new meter maybe) and then decide if this battery has enough reserve capacity before getting a bigger one.
The battery is holding at 12.69v same as when I came home. So that's definitely. 100% charged.
 
Well everything was happiness and light last evening, but not this morning.
Checked battery before going out and the volts had dropped 0.3v overnight.
Had to go out so left checking till returning.
While I was out I called for diesel and when I switched the car off - i didnt stop.
Seems I have ignition in the "Acc" position as well as "Run". It did stop on "0"
Checked it again when I got home and sure enough, first click lights everything up.
I can see £ notes blowing in the wind.
Have no idea if this is a diy or a dealer.
If the barrel can be changed then my keys should fit, but if not I guess the whole lot will need reprogramming as the immobiliser is attached.
Anyway, checked the battery drain and its still 24ma.
Tried to take the top off the sealed battery to see if acid levels are down due to possible overcharging, but no chance the cover must be glued on and I didnt want to break it.
 
Panic over -phew. Found a short in the headlight levelling wiring feeding back into acc position on ignition switch. Fuse out of levelling circuit - problem solved.
Battery drain down to 23ma.
Maybe that short drained the battery last night. Have to start monitoring again.
 
Noticed fuse for those motors missing so dropped dash to look at switches. Someone wired new feed to switch with inline fuse by switch. Took the fuse out and bingo. Strange thing the washers are supposed to be on same fuse in the fusebox but they work ok. Someone altered wiring in past methinks. Lucky this time I guess.
 
Truth be told, now I remember. I ran that additional power cable because there was no power to the levelling switch. Looks like since I pulled all the fuses last weekend lots of things on the car have started working again. Maybe the whole thing needed a "re-boot"
 
Seem to be going backwards now. Drain still showing 23ma but battery dropped 0.3v in last 24 hours. Seems to drop faster as voltage gets less. Down almost to 50% charge in 2 days. Really beginning to suspect battery.
 
In my search for answers, I have come across a bank of relays behind the glovebox.
Anyone have any info on these please ?
 
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