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Alternator issue?

dandreye

dandreye

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Location
London
Car
Accord 2L MT (CL7)
Hi All,

After jumpstarting my 2005 CL7 with a flat battery (the car has been left unattended for >3 months) the engine stalls right upon disconnecting the jumpstarter from the battery. I also tried leaving the jumpstarter connected and this way the engine stalls soon after on its own, apparently depleting the jumpstarter (it's a 16Ah/59Wh Gooloo ***an GP3000). After I give the latter some rest I can easily start the engine again with its help, so it seems the engine itself has no problems. Could it be anything else but dead alternator? It's first time I'm seeing this kind of issue.

I'm currently charging the battery to try it w/o the jumpstarter. Once the engine starts is it safe for all the electronics to disconnect the battery to see if it keeps running? Is it supposed to?

Many thanks in advance!
 
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To test the alernator you need to measure the voltage in the system with the engine running. It should be putting out between 13.8 and 14.2 volts.
 
Richard B said:
To test the alernator you need to measure the voltage in the system with the engine running. It should be putting out between 13.8 and 14.2 volts.
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Yes, but the problem is: as soon as the jumpstarter is detached the engine stalls, so nothing to measure... I doubt I'll get the right reading if I measure it with the jumpstarter still attached to keep it running, or I will?
 
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Channel Hopper said:
Find/borrow a known working battery.
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I already fully charged mine by now, so will try using it then. What is the lower threshold of the charging voltage below which the alternator would need replacing? Something like 14.8V, no?
 
dandreye said:
Yes, but the problem is: as soon as the jumpstarter is detached the engine stalls, so nothing to measure... I doubt I'll get the right reading if I measure it with the jumpstarter still attached to keep it running, or I will?
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Measure the voltage before you start the engine, and with the engine running. You will get a good enough reading to see if the voltage of the alternator is too low, with the jumpstart battery attached.

(as long as the jumpstart "battery" is not a running car with a functioning alternator).
 
Richard B said:
Measure the voltage before you start the engine, and with the engine running. You will get a good enough reading to see if the voltage of the alternator is too low, with the jumpstart battery attached.

(as long as the jumpstart "battery" is not a running car with a functioning alternator).
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Will do: thank you. No it's a standalone jumpstarter here, not another car. In fact I no longer need it now that I have the battery fully charged.
 
Right, so with the fully charged battery the engine started and kept running fine w/o any jumpstarter and the charging voltage reading was stable at 14.5V, which I understand confirms that the alternator itself is fine (I measured it with the red probe at the alternator's positive contact and the "-" probe at the battery's "-". Unfortunately I forgot to measure it afterwards at both battery terminals to check the positive cabling in between). Could anyone please explain why it was previously stalling with the flat battery upon disconnecting the jumpstarter then? Shouldn't it keep running even with the battery detached once started?
 
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The battery acts not only as a power source, but also as a stabiliser. When removed the alternator has nowhere to send the majority of the output and I would suspect the ECU shuts things down before expensive bits on the wiring loom get damaged through overvoltage.
 
Channel Hopper said:
The battery acts not only as a power source, but also as a stabiliser. When removed the alternator has nowhere to send the majority of the output and I would suspect the ECU shuts things down before expensive bits on the wiring loom get damaged through overvoltage.
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Got it: thank you. And thanks to that ECU or whatever for preventing the damage any of those components then. It's the first time that the battery was completely flat as I left the car unattended for longer than usual. On several occasions in the past it was barely able to crank the engine but still managed to start it and everything was fine.
 
It sounds like your battery is the only suspect for now. Keep the jumpstart battery charged and with you, and see how you go. If your battery is draining faster than you'd expect from just an active immobiliser/ alarm, look up some threads about "battery drain" on this forum, and work out if you have a dodgy bluetooth card. But then again, batteries don't always bounce back after being drained.

The "running a car without a battery" thing I remember from car shop talk back in the 80's (when I was driving cars from the 60s), but I rarely see it being mentioned in relation to newer cars, especially ones that save OBD codes.
 
Richard B:

Thank you. This time I left the battery disconnected to rule out any possible drainage (I use a different car daily), so it should do better when I attend the car again. Looks like I just had wrong expectations and it behaved as designed in those circumstances. Glad I didn't go for the alternator swap despite initial temptation :)

Wrt the drainage, when I'd previously leave the car on the alarm for ~3-4 weeks I was barely able to crank the engine upon return, and thought it's normal. Perhaps the battery wasn't fully charged at start although I'd normally go on a ~150-mile journey 1-2 weeks before departure. Interestingly the other car (a Lexus CT200h) survved 2.5 months this summer much better: to my great surprise exact same type Yuasa battery in it as in the Honda in question cranked the battery as if I left it just for a day. What's a typical duration that CL7/CL9 with a standard battery lasts on alarm? Or what the average amp draw w/o any drainage should be like?
 
IDK what a "normal" drain is for this generation Hondas. My 5th gen Accord drained the battery below cranking voltage when I let it sit over a 2 month holiday. My 7th gen is a diesel, so has a bigger battery. It sits undisturbed for max 1.5 weeks and has so far started OK. This is where my experience ends. A brand new battery behaves differently from one that has a few years on it, which is also a factor.

I accidentally left the car on contact for 3 hours last week and needed a jumpstart. I had no idea it sucked that much power. I had to push the car uphill a little bit to do it, which was an adventure.. (I used the wheel nut wrench as a lever to turn one of the wheels to move the car, and a brick to stop it in place while I re-positioned the wrench)
 
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