Requesting Assistance with using Relays in Car Circuitry (Preventing Counter-EMFs)

[ArcWindsor]

I see. So how long does it take for the resistance to go from 0.5 to its max? Is it literally like a split second? In other words, is the beginning current just a brief spike that shouldn't hurt anything?

If it being that brief doesn't blow the fuse, then it shouldn't hurt any of the other circuitry either (considering the fuse value has a smaller tolerance to current than any other component/wire in the circuit), right?

 

[ljcox]

I don't know how long. The current decreases rapidly from the max to the normal value. So you would get an idea from watching the lamp, ie. how long does it take to reach full brilliance?

What I'm concerned about is the possibility of contact erosion. When relay contacts close, they usually "bounce", ie. go open/closed/open/closed a few times so each bounce may slightly erode the contact material.

Note that they also "bounce" when the relay is releasing. It is called "contact bounce". In the relays that I'm familiar with, it lasts about 5 ms.

Your potential problem is when the relay operates since the filament is cold.

However, remember that I said that 2 lamps in series at 0.5 Ohm each means 1 Ohm, so the current will peak at about 14A which won't be a problem for a relay rated at 40A.

 

[ArcWindsor]

Thanks for the help so far...

Referring to my high beam DRL diagram in post#3, what would happen if both the stock relay and my relay closed at the same time? That's not supposed to happen, but if the circuit breaker relay ever stops working, then it could. So what would happen in that case?

 

[ljcox]

Thanks for the help so far... You're welcome

Referring to my high beam DRL diagram in post#3, what would happen if both the stock relay and my relay closed at the same time? That's not supposed to happen, but if the circuit breaker relay ever stops working, then it could. So what would happen in that case?

No problem.

If that happened, the driver side high beam lamp would have +12 Volt on both sides. Obviously it would not glow, but there would be no other impact such as a blown fuse.

 

[ArcWindsor]

Okay, I just stopped at radioshack and got some diodes...

1N4004
PIV: 400V
Vf drop at If: 1.6V
If: 1A
Max. Surge Current (8.3ms): 30A
Reverse current (at PIV): 30mA

My question about 1N4004: I'm using these to build an OR-gate for LEDs. The forward bias current through the diode should be less than 100mA total from the LEDs. I take it these will work fine?


1N4005
PIV: 600V
Vf drop at If: 1.6V
If: 1A
max surge current (16ms): 30A
reverse current at PIV: 10 microamps (mu-A)

My question about 1N4005: I'm using these to build the same OR-gate but for the relay coil (like you see in my above diagrams). This is for the DRL mod. I take it these should be fine for this application?

The reason I chose which diodes go with what circuit here was availability.

Thanks...

 

[ljcox]

Both diodes are suitable for either task.

Both have a max continuous forward current of 1 A & your currents are much less than that.

The max voltage ratings are more than adequate for either task.

 

[ArcWindsor]

Thanks much ljcox. I got some relays with internal suppressor diodes. I actually bought a turn signal DRL module for the DRL solution, but I also plan to implement high beam DRLs in addition but controlled by my stock fog light switch instead of with ignition (optional for bad weather). I also need to switch some other circuits with these too.

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[ljcox]

You're welcome.
Thanks for letting me know.

 

[ArcWindsor]

I just wanted to confirm that the formula "P = IV" implies the following statement:

If two high beam 55W bulbs are in parallel, together they draw 110W total (as brights). But when placed in series (such as for DRL), then each bulb runs 55/2 watts, so together, the whole DRL load would be 55W total. Or is it different than what I have said?

Also, how does the wattage map to what people refer to as 'brightness.' I know that two bulbs in series, although they have half the wattage, won't yield half brightness (because its not linear here). Do you know how this works? Also what is the technical measure for 'brightness?' Is it luminous intensity, candella, etc?

A link would be fine for the brightness question if you know a good one off hand.

Thanks again.

 

[ljcox]

As you wrote, light globes are non linear. So I expect that two 55 Watt globes in series (assuming they are incadenscent ones not halogen as I know nothing about halogens) would consume a little more than 55/2 W each since their resistances will be lower at the lower temperature (positive temperature coefficient).

I don't know what the relationship is between power consumed & light output.

Obviously, some of the power is dissipated as heat and the rest as light.

You could probably find a web site that explains it.

 

[ArcWindsor]

Will 16AWG wire will be sufficient for this load? I'm assuming it will because the load limit chart I looked up says 16AWG can tolerate something like 22A in chassis wiring. I already crimped the relay socket terminals to 16AWG wires. Should I redo it with thicker wires?

Thanks...

 

[Diver300]

As you wrote, light globes are non linear. So I expect that two 55 Watt globes in series (assuming they are incadenscent ones not halogen as I know nothing about halogens) would consume a little more than 55/2 W each since their resistances will be lower at the lower temperature (positive temperature coefficient).

I don't know what the relationship is between power consumed & light output.

Obviously, some of the power is dissipated as heat and the rest as light.

You could probably find a web site that explains it.

All bulbs are really inefficient, so just about all the power is dissipated at heat, and a tiny fraction as light. You always need to allow for the full power of the lamp to be changed into heat.

However that makes little difference to this project.

A halogen bulb at 6 V will take around 60% of the current that it takes at 12 V, so 30% of the power **broken link removed** but the brightness is far less than 30%

 

[ljcox]

Will 16AWG wire will be sufficient for this load? I'm assuming it will because the load limit chart I looked up says 16AWG can tolerate something like 22A in chassis wiring. I already crimped the relay socket terminals to 16AWG wires. Should I redo it with thicker wires?

Thanks...

The question is "What size fuse is in the circuit?"

Your first diagram shows a 10A fuse.

The wiring must be able to safely pass a significantly greater current than the fuse rating so that the fuse will blow if there is a short circuit rather than the wiring.

I'm not on expert of fuses, but I would guess that a 10 A fuse should blow at about 11 ~ 12 A.

Hence, the 16AWG wire should be adequate since you say it can tolerate something like 22A.

 

[mneary]

I just looked on the Littlefuse site at various fuses. Their ATO32V will blow within 5 seconds at 200% of its ampere rating, and within 10 minutes while carrying 135%. (They are allowed to be much faster, and generally are.) It's supposed to hold (not blow) at 110%. (360,000 seconds).

A word about "chassis" wiring application. I think they mean point to point with all around free airflow.

 

[ljcox]

Thanks for the info.

 

[ArcWindsor]

I finally got this finished.

Thanks to everyone who assisted me with this project... especially ljcox.

Everyone who replied anywhere on this thread is getting a +1 rep... IF the site allows me to do it again, that is...

When you juxtaposition two different Kelvin lights, the contrast looks interesting, as you can see below:
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The way I did it: I wired the DRL module to turn on the DRLs when I press the fog light switch. This worked out because the fog lights are disabled under the condition the DRL are enabled (low beams off). So the switch has two jobs under mutually exclusive operating conditions (at different times that don't overlap). Only one (DRL or the fogs) but not both can be turned on at a time using the same switch. Using the already-existing stock fog light switch saved me from having to add a new switch for this... nice!

The reason I wanted them to be optional instead of starting automatically with the car was because H1 bulbs are inefficient and relatively expensive to just use all the time constantly. So I only use them under more inclement weather. This works out great because there is now a new law in Ohio that requires some kind of 'headlight' during rain, and with these DRL style lights, I can avoid burning down my HID bulbs unnecessarily. I also like the way it looks in terms of aesthetics too. My car has nice 'eyes' now with the Kelvin contrast.

DRL only (kind of blurry- sorry)
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DRL with halos (the camera cannot handle the spectrum, but in person, you can see the contrast in color temp with the 8000K ring vs the yellow H1 bulb.
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I still have the option to run the halos alone (if I just shut off the fog light switch)
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Low beams on --> DRL disabled and fog lights enabled (fog switch now controls the fog lights like it does stock).
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Also, DRL mode is interrupted temporarily when I press the passing light switch (flash to pass) so all the original bright functions were preserved.

Just some pics of the job.... As you can see, it took us quite a while (my mechanic friend helped me take stuff apart). We started at 1:30AM and finished around 8AM (with many breaks in between of course).
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Once again, thanks much for the help everyone.

 

[ljcox]

I finally got this finished.

Thanks to everyone who assisted me with this project... especially ljcox.

Once again, thanks much for the help everyone.

You're welcome.

Thanks for the photos.

 

[ArcWindsor]

I just looked on the Littlefuse site at various fuses. Their ATO32V will blow within 5 seconds at 200% of its ampere rating, and within 10 minutes while carrying 135%. (They are allowed to be much faster, and generally are.) It's supposed to hold (not blow) at 110%. (360,000 seconds).

A word about "chassis" wiring application. I think they mean point to point with all around free airflow.

Thanks for the new replies on the fusing (above my pictures)...

So the chart below really isn't safe to use I take it?
American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies

If a fuse will hold for 5 seconds at 200% its ampacity, then I should select a wire gauge that can tolerate more than double the ampacity on the chart, right?

So if the chart says 16A for 18AWG, then I should use a fuse rated at less than 8A for 18AWG. Would this be a safe idea, or should I go even lower?

In other words, I'm looking for a way to create an actual load limit chart (like the link above) for myself to use that considers the time it takes fuses to blow as well as wires being in a bundle rather than all-around free air flow (because cars uses bundles).

Here is what I came up with so far....
14AWG ---> use a 15A fuse
16AWG ---> 10A fuse
18AWG ---> 7.5A
20AWG ---> 5A
22AWG ---> 3A

What do you think?

Thanks...

 

[Diver300]

It's certainly a good idea to rate fuses a little lower than the wires, and you should consider wires in bundles as having lower capacity. However, wire rating it based on how hot the wires get, and they have much larger thermal capacity than fuses, so the short term rating is taken care of. 5 seconds at twice the rated current isn't likely to do any harm.

Also, just because the fuse is rated to blow in less than 5 seconds at twice the current, doesn't mean that twice the current is a likely fault. The likely fault current depends on all sorts of things.

If the current is larger, the fuse blows much faster, so the risk of wiring damage is much less. In fact the most worrying figure is up to 10 minutes at 135% of rating, as that is long enough to get considerable heat into the cable. I would aim for the cable to be rated 1.25 to 1.5 times the fuse.

Bundling is a separate matter. The rating there depends on the size of the bundle, and how many cables are going to be taking significant current. In a car, you won't get many cables taking much current at one time. The IEE wiring regulations have a lot of information about derating for bundles.

 

[ArcWindsor]

Here are some more questions you guys can elaborate on if you wish:

Relay coils are referred to as 'inductive' loads, right?

So far, we've concluded that adding an inductive load into the car circuitry can cause damages to the car circuitry (unless properly suppressed). But is the same true backwards? In other words, if I power a resistive load by my car's inductive load circuitry, then can those inductive loads generate EMFs that can damage my resistive load circuitry?

When splicing into an inductive circuit to power a resistive load, is it the case that putting a diode in parallel with the resistive load (facing the +) will protect it in the same way?