Leaving your hazards on drains the battery much?

Random

Does leaving your hazards on drain your battery much?

And would they work if your battery was dead etc?

Anan1

ciaranfo wrote:

Does leaving your hazards on drain your battery much?

It depends on the state of your battery and how long you leave them on for. Assuming a healthy battery, a couple of hours would be fine but I probably wouldn't leave them on overnight.

A

ciaranfo wrote:

nd would they work if your battery was dead etc?

Not unless you have magic bulbs in them.:)

Random

I don't know .. I guess I had some kind of weird notion that they were partially for emergency warning lights and might have some sort of backup power .. or something .. I'll go back to bed now ..

rowanh

I left mine on over night once when i crashed my car and have to leave it on the road, about 6 or so hours later when i went back to it they were off and battery was dead. I think the battery in that car was ok, it had been changed at some stage not too long before that.

crosstownk

Hazard warning light circuits typically employ 4x21W bulbs, 2x5W bulbs and then the small bulbs in the hazard switch and the indicator lights on the dash. So this is nearly 100W of power in total. This would have draw on a 12V battery of almost 8.5A which is significant enough. As you battery voltage drops the current rises - if battery voltage drops to 10V then the draw will be 10A. Mathematically, if you had a 45Ah battery it should support the hazards for almost 5.5 hours - in reality it will be considerably shorter as the battery voltage drops increasing the current draw.

I'll get my anorak.......................

smemon

crosstownk wrote:

Hazard warning light circuits typically employ 4x21W bulbs, 2x5W bulbs and then the small bulbs in the hazard switch and the indicator lights on the dash. So this is nearly 100W of power in total. This would have draw on a 12V battery of almost 8.5A which is significant enough. As you battery voltage drops the current rises - if battery voltage drops to 10V then the draw will be 10A. Mathematically, if you had a 45Ah battery it should support the hazards for almost 5.5 hours - in reality it will be considerably shorter as the battery voltage drops increasing the current draw.

I'll get my anorak.......................

o...k......

Random

Thanks

RoundyMooney

crosstownk wrote:

...in reality it will be considerably...

...longer!

The bulbs are not burning continously. Assuming they are on 50% of the time, your five hour estimate becomes nine, which is about right for a 45Ah battery.

Hotblack Desiato

crosstownk wrote:

As you battery voltage drops the current rises

No it doesn't, I=V/R according to Ohm's law.
If what you said was true, there'd be no such thing as an energy crisis, and instead of charging up my battery to start my bike I'd be discharging it first!

Hotblack Desiato

RoundyMooney wrote:

The bulbs are not burning continously. Assuming they are on 50% of the time

When the bulbs aren't on, the battery is powering a little heating element inside the flasher unit. When it heats up, it breaks the circuit to itself and makes the circuit to the bulbs. Then it cools down, contracts, breaks the circuit to the bulbs and makes the circuit to itself... So when the bulbs aren't lit there's still some current draw.

Alun

ninja900 wrote:

When the bulbs aren't on, the battery is powering a little heating element inside the flasher unit. When it heats up, it breaks the circuit to itself and makes the circuit to the bulbs. Then it cools down, contracts, breaks the circuit to the bulbs and makes the circuit to itself... So when the bulbs aren't lit there's still some current draw.

Maybe on a 1965 Ford Anglia ... modern cars are a little more, shall we say, "sophisticated".

maidhc

Alun wrote:

Maybe on a 1965 Ford Anglia ... modern cars are a little more, shall we say, "sophisticated".

I would have thought the flasher units still work on the same basic principle. Very simple effective and reliable.

crosstownk

ninja900 wrote:

No it doesn't, I=V/R according to Ohm's law.
If what you said was true, there'd be no such thing as an energy crisis, and instead of charging up my battery to start my bike I'd be discharging it first!

Yes you are correct. I was simply working on W=VI, and took the assumption that the energy output remainied constant. This was simply for illustrative purposes only, and is not the case in reality. What I described assumed that the bulbs did not loose any brightness as the battery went flat. I reckoned it was easier to describe it this way rather than using Ohm's law. Apologies, it was not intended to be misleading.

Alun

maidhc wrote:

I would have thought the flasher units still work on the same basic principle. Very simple effective and reliable.

Not for a good many years now ... most are solid state these days

In fact, on more modern cars equipped with CANbus, it can get a whole lot more complicated. In such systems the light clusters are independently functioning units and respond to commands sent to them over the CANbus network from a central control unit, in the case of the indicators, probably the instrument cluster. In other words, a command will be sent to the appropriate light cluster(s) to say "start flashing" and "stop flashing". Same kind of thing for sidelights, brake lights etc. Cuts down on wiring loom size a lot since the CANbus is just a single twisted pair cable.

crosstownk

Alun wrote:

Not for a good many years now ... most are solid state these days

In fact, on more modern cars equipped with CANbus, it can get a whole lot more complicated. In such systems the light clusters are independently functioning units and respond to commands sent to them over the CANbus network from a central control unit, in the case of the indicators, probably the instrument cluster. In other words, a command will be sent to the appropriate light cluster(s) to say "start flashing" and "stop flashing". Same kind of thing for sidelights, brake lights etc. Cuts down on wiring loom size a lot since the CANbus is just a single twisted pair cable.

Yes, more and more vehicle manufacturers employ this system. The only downside is that the indicators do not flash 'double time' to indicate(sorry!) a blown bulb.

Alun

crosstownk wrote:

Yes, more and more vehicle manufacturers employ this system. The only downside is that the indicators do not flash 'double time' to indicate(sorry!) a blown bulb.

Some do actually .. a system monitors the current flow when they're operating and then commands the remaining indicators to flash twice as quickly and/or display an error message on the on board display. Some are even capable of drafting another bulb, say a sidelight or brake light as a stand-in indicator bulb!

crosstownk

Alun wrote:

Some do actually .. a system monitors the current flow when they're operating and then commands the remaining indicators to flash twice as quickly and/or display an error message on the on board display. Some are even capable of drafting another bulb, say a sidelight or brake light as a stand-in indicator bulb!

Correct. Mercedes uses the side light bulb as an indicator when the main indicator fails. Which, incidentally, will result in longer 'hazard warning life' as the side light is only 5W vs the 21W of the main indicator

Esel

I say we all try it and post the results. A Bertie anorak to the poster who can flash the longest (without getting arrested!)