oosmanlele

I have RX350, just a few thousand miles on it. I bought a new battery last year. Now the battery does not keep charge.

Battery light on the dashboard is not on.

I disconnected the neg- battery cable, and put the multimeter between it and the battery terminal. There was almost 0 current.

Then I attached the cable back to the battery and jump started the car. I checked the voltage across the terminals. It was around 14 V dc, but it was also around 30 V ac.

What does that mean? Is the diode on the alternator blown?

Thanks.

salimshah

If you checked the standby current provided by the battery [rx off] and you got 0 mA then something is wrong, with the way you are measuring or the battery is dead. I expect the standby number around 220mA

AC voltage that your meter showed can be a shifter AC (voltage varying above 0v line ... (ex: half wave rectifier produced only produced the + part of the input wave and only when you connect a cap, you get the charged up dc value). The battery should act like the cap.

Go to an auto shop who sell batteries and have your RX tested for free.

Salim

oosmanlele

The battery was giving 6V when I tested for the current, and it showed almost 0 current reading.

gusar

You cannot measure DC with setting of AC on your multimeter. And you have DC on the battery. Just ignore AC reading because it shows total BS (number depends on the type of multimeter, not the real voltage).

oosmanlele

Well, if the alternator diode is busted, then it will be sending out AC voltage that can be detected by the AC voltmeter. That is what I was trying to see if the diode is busted or not.

However I checked the same thing on another car that works, I got the same ac output.

salimshah

welcome to the world of hands on electronics

You need to go beyond the basic book understanding of DC-AC voltage. What you are measuring on, AC scale, is the ripple (the changing voltage) level that is on the rectified DC voltage. [the value does not go below zero hence it is dc] but changes as the alternator produces peaks. If you have a scope handy, set it on DC and you can see the varying voltage in DC domain.

These spikes are the noise in the charging system.

Salim

salimshah

6volts from a 12v battery is a dead battery. You can damage your charging system by trying to charge it up.

Discharged battery should put out atleast 10+v under no load. If you have a severe short [too heavy a load for a discharged battery] it can fall below 10volts but then your current should register high value [which is not the case based on your previous post].

Lastly, to check out the charging system you need to have a battery in a reasonable condition. Any data that you get with a bad battery to begin with should be thrown out of consideration.


Salim

biff44

"I disconnected the neg- battery cable, and put the multimeter between it and the battery terminal. There was almost 0 current. "

except for very special multimeters, most are fused to only handle 10 amps of current. What you likely did was blow out the fuse inside of the multimeter on the amps setting. After that, any current would read "0". Since the fuse is only in the amps portion of the circuit, it will still function as a volt meter, so you probably do not realize it was blown out.

oosmanlele

Thanks Salimshah and Biff44 for your comments. I took the battery to Sears, where I had bought it from. They charged it overnight, then tested it. The battery was good. I brought it back, put it in the car and started it. I removed the neg- terminal while car was running. Car engine kept running like nothing had changed. So it seems the charging system is also good.

I bought a new Multimeter. Put that between the neg- terminal of the battery and the cable. Car is not running. The Amps read about 0.650A at first, then quickly drop to 0.250A and stay near that value. Now Salimshah said he was expecting 220mA for standy, this is close to that.

I also checked the current on my other car, Honda Odyssey. The standby current is 50mA.

Is 250mA standy current high enough to drain the battery if its not used for a couple of days? What is the normal standby current for RX350?

How can I test the relays, perhaps one is shorted? Where are they located? I see a fuse box on the driver side, but no relays.

Thanks

gusar

No. For a good battery it would take about 1.5 - 2 weeks to drain it under this current. But for a bad battery - yes.
It looks like you need a new battery, better have it earlier to spare some troubles for yourself... Not huge money.