6G Celicas Forums

At first I thought my battery wasnt holding its charge. But with my new setup I found out with a multi meter that power is dropping as soon as the engine is off.
I did a parasitic drain test and discovered that by dis connecting my alternator, it stopped dropping!!!
WTF????
Can somone pls explain as to how its possible my alternator is draining power when off?

This post has been edited by yellowchinaman: May 22, 2014 - 12:07 PM

How much is it pulling?

About 0.1V every 20 seconds. Im watching it drop on the volt meter.

Found this on youtube and its exactly the same
http://m.youtube.com/watch?v=oHKUvB5oHIA

This post has been edited by yellowchinaman: May 23, 2014 - 6:49 AM

Are you sure you posted the right video, because there appears to be nothing wrong with that car.

The battery voltage is dropping? The battery usually has to stabilize after charging, but if it continues to drop it may be bad.
If you are performing a parasitic drain test your multimeter should be set to milliamps in DC, not voltage. Amperage is the measure of current flowing, voltage is simply the measure of the potential of energy between two sources. There should be 5 to 20 milliamps (mA) present in most vehicles. Make sure you remove either the negative or positive battery clamp and use the multimeter probes to bridge the gap between the battery post and clamp. This way, electricity flows through your multimeter to complete the circuit, and the multimeter can measure the amount of energy flowing through the electrical system. Just dont turn on a bunch of lights or power on the car with the multimeter bridgeding the circuit, I wouldnt even recommend opening the doors. Most amateur multimeters can only handle 3-10amps tops while measuring amperage before they blow their fuse or short out. If you determine you have a higher than normal drain on your battery, you should pull the fuses one at a time and to find which specific circuit is pulling the excess current. Voltage is irrelevant to this test, it can only be used to test the relative charge of the battery and whether the alternator is functioning.

If electricity was water, amps would be the speed at which water flowed through a pipe. Voltage would be the pressure difference between the inlet and the outlet of the system, or the height difference between the water tower and your faucet. Resistance could be considered the diameter of the pipe and power or wattage would be the liter per hour flow through the pipe.

The alternator could create odd voltages when powered down, it is a magnetic core which spins. These magnets could cause fluctating, miniscule amounts of voltage even at a dead stop. There are diodes present in the alternator which should prevent it from consuming electricity, they also have a shutoff circuit below ~500rpm so that the starter isnt trying to turn the alternator when you start the car. If alternators werent designed this way as well as being AC instead of DC, they would spool up like an electric motor when connected to the battery.


Sorry if I'm talking down to you in any of this, I know you probably already know most or all of what I said but its hard to gauge from the short posts on this topic. My minor is going to be Electrical Engineering.

This post has been edited by Special_Edy: May 22, 2014 - 5:06 PM

It could be a bad diode in the alternator, but as was said you need to measure the actual draw not just the volts dropping and make sure it's the alternator and not something else on the circuit. Which did you unplug from the alternator, the harness or the battery cable? If it's the battery cable then there's a good chance there's a diode gone bad shunting to ground all the time bleeding out power, if the connector was unplugged then you need to make sure there's nothing on the circuit drawing.

Got it fixed?

No. Ive been putting it off. I think its what you said bitter. Diad failure. But not sure how to resolve it. May just buy a new alternator but at a later date.
I dont know know how long its been like this but I guess ive lived with it for that long it doesnt hurt to leave it a bit longer.

Denso alternators are pretty easily rebuilt, you could sand the commutator, put some new brushes in, and a new diode pack and likely have a working alternator for another 10 years for less than 1/2 the cost of a new one and a 1/2 day of work. I'm sure the dealer sells some kind of rebuild kit.

On the other hand, swapping a newly rebuilt one or a new one in is much much easier and more time efficient.

The diodes rectify alternating current into direct current.

You can test if your diodes are bad by measuring the voltage across the battery terminals while the engine is running. Normally there is 13+volts DC and <.10volts AC. If your multimeter is set to volts in AC and you get a significant reading you have a bad diode. It is called alternator ripple and you are performing an alternator ripple test.

Yep, that's a good test. I don't know if that'll show one that's stuck shunting to ground though, like would cause a constant drain.

So does anyone know how I can fix the diode problem? I cant find a kit.

https://www.google.com/search?q=toyota+alte...22&ie=UTF-8

https://www.google.com/search?num=30&cl...284.pyFv0KpIA-A

You need the alternator part number to know what kit to buy. Did you call the dealer to see if they sell one?

And I/you don't know if you have a leaking vreg or leaking rectifier, so you need to learn to diagnose that first.

Heck, you need to determine how many amps you're loosing through the alternator yet too and through which connection/circuit.

This post has been edited by Bitter: Jun 14, 2014 - 9:46 AM

Yes do a real test. Parasitic drain test or alternator ripple test as detailed above.

If you are absolutely convinced something is wrong with your alternator(specifically that you think its draining the battery) then do the parasitic drain test on the alternator. Measuring voltage will tell you absolutely nothing other than the relative charge of your battery or whether the alternator is charging the system while the engine is running. Amperage is the presence of flowing electricity, voltage is merely the potential of a source of power AT REST.

I'm wondering if he was just seeing his cap/lipo battery pack discharging due to self discharge of the caps and normal parasitic of the car on the very small amp hour lipo pack.

The LiPo and Capacitors dont experience voltage drop typical to Lead-Acid batteries. Lead-Acid delivers > 12.4volts above a 75%-85% charge, voltage begins to sharply drop below this point. Lithium batteries and capacitors will deliver peak voltage until a fraction of a full charge, perhaps even a few percentage of a full charge, before the voltage drops significantly.
I cant find a decent chart to illustrate this characteristic, maybe I need to gather several battery types and chart their performances on a benchmark test. This is the best I could find on teh interwebs-

Its not the lithium and caps. I did the test before I did the change.

I located the battery he's using, it's only rated for 6 amp hour and 150CCA which is awfully tiny for a car to use, especially with ignition off draws. Assuming a 30 miliamp draw it would take about 20 hours (6 amp hour/0.030 amps draw) to drain the battery flat dead. I believe that battery is just too small to use in a car. 30 milliamp is assuming the normal draw for a stock car with no add ons like alarms or aftermarket radio's that consume more power with the key off. I do hope it was just a bad alternator and not the battery being too small, and that my math is wrong.

I forgot a zero, 200 hours until totally dead, but at 1/2 capacity I doubt that battery would start the car.

This post has been edited by Bitter: Aug 24, 2014 - 11:35 PM

I dont depend on the battery to start the car since the capacitors do all the work.

Caps have to draw off something don't they? They're constantly being depleted by the 30 miliamp drain, which is in turn pulling on the battery to keep them full, right?