HID and Relays

[Slug]

Is there a trick I am missing?
Just buggered up my second one now.... first was a no name cheapie but the second a Hella 30A jobbie. Both seem to click on power but don't switch.

Anyone else fried one for no apparent reason?

Cheers
Dan

[bushy555]

Anyone else fried one for no apparent reason?

"Fried" as in the relay fried or the ballast fried?

[Slug]

Just the relay

[chimpboy]

Out of probably hundreds of standard 30A relays I've handled over the years I've probably not seen more than one or two fail.

Is it possible you're making a wiring error?

[-Scott-]

Not something silly like 24V system & 12V relay?

Define "fried" - to me, that's either burnt coil or welded contacts, so I wouldn't expect it to "click". Can you supply more detail, such as vehicle and either wiring diagram/description of connections?

[Slug]

99 GU Patrol running 2 50W HID's in Hella 4000 cases. Am using a standard relay @ 30A. When they fail, I can hear the relay click but checking it with the circuit tester it doesn't power the output pin.


85 Ground wire is good, checked it tonight and gave it a polish with wet and dry just in case.

86 Trigger from high beam seems to be fine.

30 Power in comes straight from the battery through a 20A circuit breaker using a heavy, short piece of wire.

87 Power out to the spotties is via a pair of heavy wires about 5mm in dia.

Wiring seems fine but something is definitely not right
My only other thought would be a crook circuit breaker?

[cmcd]

Do they work with a normal halogen spottie? That'd at least eliminate the HID causing them to fail..

[Slug]

They did and do work as they should in between failures..... just strikes me as bizarre given the standard style relay rarely fails.

Just wondered if it could be the HID ballasts feeding back into the relay

[chimpboy]

Pop the dead relay open and have a look inside. You might as well since it's broken. At least you will be able to see if the contacts are burned out or whatever. Besides everyone should look inside a relay at least once

I can't really see why an HID ballast would kill a relay unless it is defective. And I am struggling to think what kind of defect in the ballast could kill the relay anyway.

Other thing to try might be to bypass the circuit breaker temporarily in controlled conditions when the relay is "dead".

[da60]

Even though you are using a 30amp relay, when HID's start up they pull more than the rated power (eg your 50w set-up). I think from memory that even 35 HIDs pull about 70w on cold start-up. Which working with that formula you would be pulling about 38amps if your using all 4 50watt HID's on start-up. The person to confirm this with would be Bushy 555 as he is a pretty cluey guy.

[chimpboy]

Even though you are using a 30amp relay, when HID's start up they pull more than the rated power (eg your 50w set-up). I think from memory that even 35 HIDs pull about 70w on cold start-up. Which working with that formula you would be pulling about 38amps if your using all 4 50watt HID's on start-up. The person to confirm this with would be Bushy 555 as he is a pretty cluey guy.

50W @ 12V = 4.2A

times two lamps = 8.4A

allowing even double the current pull for a cold start = 16.8A

One of us is making an error

Anyway, it's been over two weeks since slug asked the question, it would be interesting to hear how it turned out.

[Red Dog 4x4]

With A 55w hid thay pull about 20 amps each light i have 6 55w lightforcec lights on my truck (GQ tray back) what i have done is wire up two relays for two spot lights, so in my case i've got a total of 6 30 amp relays, 6 30amp fues then 6mm twin core wire to the blassats. Never had any probles in the two months thay have been on the truck avrage of 160km a night...

[chimpboy]

With A 55w hid thay pull about 20 amps each light i have 6 55w lightforcec lights on my truck (GQ tray back) what i have done is wire up two relays for two spot lights, so in my case i've got a total of 6 30 amp relays, 6 30amp fues then 6mm twin core wire to the blassats. Never had any probles in the two months thay have been on the truck avrage of 160km a night...

I just need someone to explain how a 55W lamp can pull 20 amps at 12V, since P=IV (or I=P/V), which makes 4.5A. Even allowing for some extra pull at start-up 20A seems wrong.

But I've never fitted an HID so I may be missing something.

[Red Dog 4x4]

Its only on start up that thay pull that much, thay need a lot of power to start up, thats why thay have a blast unit. then once thay are "warm" thay drop to around 4 amps.

[cmcd]

With A 55w hid thay pull about 20 amps each light i have 6 55w lightforcec lights on my truck (GQ tray back) what i have done is wire up two relays for two spot lights, so in my case i've got a total of 6 30 amp relays, 6 30amp fues then 6mm twin core wire to the blassats. Never had any probles in the two months thay have been on the truck avrage of 160km a night...

I just need someone to explain how a 55W lamp can pull 20 amps at 12V, since P=IV (or I=P/V), which makes 4.5A. Even allowing for some extra pull at start-up 20A seems wrong.

But I've never fitted an HID so I may be missing something.

http://www.youtube.com/watch?v=NCqjSLUIkjk

According to the comments, that's a single ballast from a 2001 Lexus GS-300 (which as far as I can find on the web is 35w).

[chimpboy]

Its only on start up that thay pull that much, thay need a lot of power to start up, thats why thay have a blast unit. then once thay are "warm" thay drop to around 4 amps.

http://www.youtube.com/watch?v=NCqjSLUIkjk

According to the comments, that's a single ballast from a 2001 Lexus GS-300 (which as far as I can find on the web is 35w).

Good info.

I wonder if some ballasts are better than others for this. Because it makes the wiring a bit bulkier, one relay per ballast... sheesh. I guess single 60A for each pair would take up a bit less space at least.

[da60]

These are spec's for a 35w HID system that I pulled from a site.
If you apply the same sort of formula's to a 50w system he is pulling more current than a 30amp relay can provide.


Ballast Input Voltage (nominal) 13.5V
Ballast Input Voltage (operating) 7V to 21V
Ballast Input Voltage (startup) 9V to 16V
Ballast Input Current (startup @13.5V) 8A
Ballast Input Current (startup @9V) 15A
Ballast Input Voltage (steady state @13.5V) 3A
Ballast Input Voltage (steady state @9.0V) 4.7A
Ballast Output Frequency 400Hz
Ballast Output Current (startup) 2.4A @25V
Ballast Output Current (operating) 0.41A @85V
Light Source (startup) 25kV
Light Source (operating) 68V to 102V

[Shadow]

These are spec's for a 35w HID system that I pulled from a site.
If you apply the same sort of formula's to a 50w system he is pulling more current than a 30amp relay can provide.


Ballast Input Voltage (nominal) 13.5V
Ballast Input Voltage (operating) 7V to 21V
Ballast Input Voltage (startup) 9V to 16V
Ballast Input Current (startup @13.5V) 8A
Ballast Input Current (startup @9V) 15A
Ballast Input Voltage (steady state @13.5V) 3A
Ballast Input Voltage (steady state @9.0V) 4.7A
Ballast Output Frequency 400Hz
Ballast Output Current (startup) 2.4A @25V
Ballast Output Current (operating) 0.41A @85V
Light Source (startup) 25kV
Light Source (operating) 68V to 102V

A 30amp relay can handle peak currents in excess of its rated current.

It is rated to pass 30amps 24/7, Most devices you switch with a relay have an inrush current. HID's are no different.

[da60]

How much over the 30amps can a relay handle? (ie. I know that electric motors pull max amps just on start-up) Would it handle a inrush current of up to 50amps?

[chimpboy]

These specs are for Hella relays. Most decent brands would be comparable.

These three are the most common relay types in general automotive use, the middle one is the typical one you'll find on sale most places.

AFAIK the double-throw relays are usually less capable on the "NC" terminal, someone may know specs for this.

In theory these can handle pretty big inrush currents, more than I would have expected.

[chimpboy]

and for Omron relays, probably more of a match for typical aftermarket relays?



(G8JN / figures D and E)

The thing to note is probably that the continuous current is 35A and the inrush is 100A.

Just posting these in case they're useful.

[chimpboy]

Other possibly useful specs here:

http://www.keefeperformance.com/kprelay.html

They give different ratings for lamp loads vs motor loads, I would be interested to learn why..?

[da60]

thanks for that, I was a bit concerned as I had 4 hids on my truck and didn't even thing about inrush current.

[chimpboy]

thanks for that, I was a bit concerned as I had 4 hids on my truck and didn't even thing about inrush current.

Me neither, this has been a useful thread for my edumacation.

[Shadow]

Other possibly useful specs here:

http://www.keefeperformance.com/kprelay.html

They give different ratings for lamp loads vs motor loads, I would be interested to learn why..?

a motor is a big inductor.

an inductor at it's rudimentary level opposes a change in current.

So when you switch off the relay, the motor will induce a larger than supply voltage as it tries to maintain the current flow. This large induced voltage can arc across the relay contacts at the very large current which will shorten the life of the contacts.

Switching a resistive(lamp) load does not suffer from arcing on the contacts to the same extent.

[chimpboy]

Thanks. I found a useful reference but it seems to be mainly about AC stuff; please tell me if it's not accurate for DC:

# What is the difference between resistive, inductive, motor, and lamp loads?

We must express the load as a contact rating, which is the electrical load-handling capability of relay contacts under specified conditions and for a prescribed number of operations or life cycles.

RESISTIVE LOAD: A resistive load usually consists of some sort of resistance in the circuit; e.g., heaters, resistors, etc.

INDUCTIVE LOAD: An inductive load consists of a load created by a wire wound coil, such as in a relay or solenoid, a transformer, or any load which uses a winding over a magnetic iron core. Breaking an inductive load is usually more severe than breaking a resistive load and will generally produce heavy arcing.

MOTOR LOAD: A motor load can be referred to as a rotating inductive load, generally with a high inrush of six times the normal load. The breaking of the load is much the same as a resistive load.

LAMP LOAD: There are many types of lamp loads such as tungsten filament, fluorescent, mercury-vapor, and other exotic gas lamps. The loads we normally concern ourselves with are tungsten filament. Tungsten filament lamps, when first turned on, will draw an inrush current of 10-15 times of the steady-state current. The inrush is similar to a motor load inrush and is caused by the cold filament in the lamp. After the lamp filament has heated up, the current will drop to its normal level. Most tungsten filament lamp load ratings are 20% of a resistive load.