2008, two-click noise from rear normal on startup?

[Snagtooth]

I tried some searching and did not find it so I hope this is not a duplicate thread - but, is it normal for two clicks to be heard from the rear of the car on startup? It almost sounds as though someone is flipping a switch on and off twice or perhaps like the click heard when you switch your bright lights on and off.

Although I have had the car a couple of weeks, I just noticed the noise and can't recall if it was always there and for whatever reason I am just now "noticing" it. Everything seems to work and run fine, so perhaps this is a normal noise.

many thx.

[blazer_5154]

Mine also makes this noise, although I am not sure exactly what it is, I'm pretty sure that it is normal. My guess would be that it might be the sound of the HV relay contacts engaging. From my limited experience with home-build EVs this seems similar, but I'm sure someone here will correct me if I'm wrong.

[tlaine]

Pretty sure mine did the same, always thought it was normal a computer clicks when you power it up so figured it was similar.

[john1701a]

Originally Posted by Snagtooth

I hope this is not a duplicate thread

After 8 years of forum discussions, there's pretty much nothing that hasn't already been asked...

Drive a Classic Prius when it's -10 F. That makes it very easy to identify the aspects of hybrid operation. There are a number of predictable clicks from the electric component relays.

With the HSD Prius, you can't really hear any of that from the engine and basically only from the battery-pack during startup when the seats are down.

It short, that's normal.

.

[Snagtooth]

thx for the replies.

The computer analogy is a good one, because now that I think about it - it almost sounds like a computer monitor/LCD clicking on and off during boot up.

Does any of the Prius experts know what this is that actually makes the noise? Curiousity has got me now, especially since it sounds like it comes from the rear of the cabin.

[devprius]

The two clicks are the high-voltage relays. They are used to isolate the high-voltage battery pack from the rest of the car when you are not driving it. When you press start, the computers boot up via the small 12-volt battery, and seeing that everything is fine, bring the high-voltage battery pack online so that the car can be driven.

[Snagtooth]

Ah I see, thanks for clearing that up for me. This car is a marvel of technology!

[Patrick Wong]

Snagtooth, you must have excellent hearing. The only time I noticed the three relays clicking (located within the traction battery metal enclosure) is when I had a flat tire on my 2004 and had to drive the car without the folding hatch cover installed. If you can hear the relays upon startup, you should also be able to hear them when you shutdown the vehicle.

The reason that you hear two clicks upon startup is because there are three relays. One is for the negative side of the battery while one is for the positive side of the battery including a current-limiting resistor. The third relay bypasses the resistor after a short delay, allowing the electrolytic capacitors in the inverter to charge up.

[Snagtooth]

LOL, actually my hearing is pretty acute, but I think my relays are just louder than maybe some for whatever reason. Maybe it's the acoustics on the 2008 models is different?

My wife and passengers can hear them too usually if they are paying attention and I point it out. Your right on the shutoff, though not as loud (or maybe my hearing has adjusted to road noise) I can usually hear the clicks on shutoff too.

[qbee42]

Sometimes I can hear the relays click on my 2006. Sometimes they snap with a bit of an electric arc sound. Mostly I don't hear them.

Tom