Relay capacity

How much AMPS are they rated for on a continuos basis. I am refering to the MINI relays found in the PDM of the 1996 and newer XJ's. I will be building a headlamp harness and think they would not hog too much of the already non-exsisting free space in the engine compartment. A trip to Pick & Pull would net me all the necessary components.

Why not go with fullsize 30amp relays???They're not very much bigger than the mini's

for some reason I remember 20amps from somewhere for the smaller ones.....

Regardless they'll handle what you are going to use them for.How many amps will your headlights be drawing?Stock is 55w 4.58 amps....even if your headlights were drawing something crazy like 80w that would only be 6.6 amps.
I would use one relay for the highbeams and another for low beams.....

Thanks. That is good to know. I was thinking more in the line of 2 relays per lamp, 1 each high beam and low beam. The lamps are the regular H4 55\65 watts.

DIN relays (1" cube) are rated for 30A typically, but I've seen some at 40A.

Mini-DIN relays (the ones you're probably talking about - they're about 2/3 the size) are usually good for 15A each, IIRC. I'd have to look to be sure, but that sounds right (I'd probably not push them past 10A.)

Figure circuit load by taking the nominal wattage and dividing by a nominal 12 volts - the answer will be in amperes. Bear in mind that "nominal" voltage is somewhat lower than "operating" voltage - thusly:

"Nominal Design" voltage is 12VDC.
"Nominal Operating" voltage is 13.0-13.6VDC (depending on who you talk to.)
"Actual Operating" voltage is usually ~14.0VDC (varies by system and load.)

Given a specific power rating (Watts,) an increase in operating voltage results in a decrease in operating current, as in:

65W @ 12.0VDC = 5.4167A
65W @ 13.0VDC = 5.0000A
65W @ 13.6VDC = 4.7794A
65W @ 14.0VDC = 4.6429A

So, if you design for a nominal voltage of 12.0VDC ("nominal design") you'll be building in a comfortable margin. Thus:

2 x 65W = 130W @ 12.0VDC = 10.8333A. Therefore, your full beam circuit should be designed to handle a current of 11A in total - the mini-DIN relay will handle that fine. For your dip beam, 2 x 55W = 110W @ 12.0VDC = 9.1667A, design for 10A maximum draw.

Make sense? Using mini-DIN relays will allow you to run a simpler spares box, but it's a cinch you're also using full-size DIN relays in your rig - so you should keep those around anyhow. Might as well design for full-size DIN relays - since that gives you more room for upgrading later.

ditto. smaller ones are good for 10-20, but i wouldnt go 20 continuous on them.

techno1154 said:

Thanks. That is good to know. I was thinking more in the line of 2 relays per lamp, 1 each high beam and low beam. The lamps are the regular H4 55\65 watts.

Click to expand...

thats unnecessary redundancy.....and a waste of wire.
go with one relay for both lamps for the lows and another relay for the highs.

I am going to go with with four. Another 5 bucks and couple feet of wire.
http://go.jeep-xj.info/HowtoHeadlightLoom.htm

Pelican said:

I am going to go with with four. Another 5 bucks and couple feet of wire.
http://go.jeep-xj.info/HowtoHeadlightLoom.htm

Click to expand...

Do as you will - but I'm designing my harness to use two relays and two fuses (dip and full beam) to reduce points of failure. If your full beams go out, replace the full beam relay or fuse (whichever is shot - check the fuse first.) Likewise the dip beams.

Simplicity can be important, especially when you've got to fix something out in the arse of nowhere... Also makes the spares box lighter, and reduces potential need for field testing.

5-90 said:

Do as you will - but I'm designing my harness to use two relays and two fuses (dip and full beam) to reduce points of failure. If your full beams go out, replace the full beam relay or fuse (whichever is shot - check the fuse first.) Likewise the dip beams.

Simplicity can be important, especially when you've got to fix something out in the arse of nowhere... Also makes the spares box lighter, and reduces potential need for field testing.

Click to expand...

What is the projected market date? How it the Beta unit holding up?

Pelican said:

I am going to go with with four. Another 5 bucks and couple feet of wire.
http://go.jeep-xj.info/HowtoHeadlightLoom.htm

Click to expand...

can I ask why?Do you have eight headlights?
For that matter why not go with eight or even better twenty!!!
You guys must get off on wiring needless shit....

techno1154 said:

What is the projected market date? How it the Beta unit holding up?

Click to expand...

It mainly depends on when I get my tax return, as I've been clobbered with incidental expenses of late. The betas have done well (I'm actually pleased that one didn't work, as it will give me a chance to figure out what sort of hitches I'm likely to run into.)

I need to recall the protos, perform a DA on them, make a few revisions, and issue the "production" versions to the beta testers. If they go easily and well, it goes into production "built to order." It's a bit more complex than battery cables (natch!) and they're all hand-built, and a bit more testing is involved (need to figure out how to automate that to reduce potential error and simplify things.)

So, I'm hoping to get things going in the next 4-6 weeks at this point - the big problem is that we've been clobbered since December due to my MIL being ill over and over again - and it's taken up a lot of my time and discretionary funding (at $3/gallon and all the running about? Yech.)

outlander said:

can I ask why?Do you have eight headlights?
For that matter why not go with eight or even better twenty!!!
You guys must get off on wiring needless shit....

Click to expand...

Using 4 relays do not mean that the XJ has 8 headlamps or 4 for that matter. A person (including myself) may choose to use 2 relays per headlamp ie; each headlamp have a relay for high beam and another for low beam. It is called choice. I did that on my 1994 XJ. 4 relays, 2 headlamps and yes 4 fuses one each relay. That XJ got stolen back in 2003 (that is not relavant at this time).

techno1154 said:

Using 4 relays do not mean that the XJ has 8 headlamps or 4 for that matter. A person (including myself) may choose to use 2 relays per headlamp ie; each headlamp have a relay for high beam and another for low beam. It is called choice. I did that on my 1994 XJ. 4 relays, 2 headlamps and yes 4 fuses one each relay. That XJ got stolen back in 2003 (that is not relavant at this time).

Click to expand...

I'm not arguing that it's your choice to do so - I was just trying to point out that you're unnecessarily complicating things. That's all.

You can split the lamp circuits and use two relays per lamp (in parallel) if you like - I won't stop you. Just expect me to ask why you're making things difficult for yourself, that's all (If you need a bigger relay than a 30 DIN, you can get 75A relays from Bosch as well - they're used for secondary power distribution. 75A x 12VDC = 900W, I don't know if you're going to use lamps that big. Hell, I don't know if you can find lamps that big yet!)

well he's right,it's called choice.To each their own......

outlander said:

well he's right,it's called choice.To each their own......

Click to expand...

Ayuh. Honestly, I just hope he does take notes on his project - he's likely to need them.

"Simplicity" is a key component of my designs - the more you complicate something, the more points of potential failure are introduced and the more headaches you have troubleshooting. Why buy trouble, when you get plenty for free?

I know......
Atleast we tried to give good advice,though.