Still dropping voltage after installing relay kit

crdiscoverer

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I recently made the jump from my old 7" Hella VisionPlus H4 headlights to a Koito kit containing the headlights, bulbs and a relay kit (all Koito/Osram branded, even the relays and fuses). I measured voltage drops before and after installing the relay kit, using Daniel Stern's instructions. Before I was losing almost 4v with bulbs receiving around 9v total. It's much better now but I'm still confused. So here are the numbers:

Furthest side from battery:
Battery positive to low beam positive drop = 0.694v
Battery negative to H4 ground drop = 0.408v
Total drop is around 1.1v

I'm confused, especially about dropping so much voltage on the ground side. Being a universal kit, wire length is very generous (I think it's 16AWG but I can't see markings anywhere as it's mostly covered in a protective sleeve). I had to zip tie the excess, in total probably around a meter+ including far-side bulb wire + relay wire + fuse wire. In short, wire to the relays and fuses is quite a lot more than I need (it's a small engine bay). Should I begin by trimming the excess wire? I'm afraid my trimming won't be of such a high quality as the kit and I may end up losing more volts.
 
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hamhanded

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That's what I'd suspect first too. Is there any way you can jump it temporarily with shorter, higher gauge wire? That would tell you pretty quickly.

If you know how to solder I'd recommend using soldered connections under shrink tubing instead of crimp butt connectors. If you do that, you can be sure any resistance added by your connections will be more than offset by all the excess wire you removed.
 

LEDphile

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An H4 lamp draws about 5A, so for your 1.1V drop, that's about 220 mOhm resistance throughout the circuit. Remember that the contact resistance of a connector is on the order of 10 mOhm, 16 AWG wire is about 4 mOhm/ft, and that fuses, fuse holders, and relays all add up.

Assuming it's 10' as the wire runs, you've got 80 mOhm just in the wire (10' x 4 mOhm/ft x 2), plus another 40 mOhm in the fuse holder and relay socket, plus whatever's in the relay and fuse. So if you do everything perfectly, you might cut the voltage drop in half (and reduce it further by moving to thicker wire), but you're getting into the realm of diminishing returns here.
 

crdiscoverer

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That's what I'd suspect first too. Is there any way you can jump it temporarily with shorter, higher gauge wire? That would tell you pretty quickly.

I did that before the relay kit got here and I got the full ~14 or so volts straight from the battery terminals, so at least I know the battery itself is not the culprit. I entertained the thought of adding a ground closer to the furthest headlight to recover at least those 0.4v. I need to test the other headlight too. That'd also tell me if wire length is the main issue or something else. I'll report back.

An H4 lamp draws about 5A, so for your 1.1V drop, that's about 220 mOhm resistance throughout the circuit. Remember that the contact resistance of a connector is on the order of 10 mOhm, 16 AWG wire is about 4 mOhm/ft, and that fuses, fuse holders, and relays all add up.

Assuming it's 10' as the wire runs, you've got 80 mOhm just in the wire (10' x 4 mOhm/ft x 2), plus another 40 mOhm in the fuse holder and relay socket, plus whatever's in the relay and fuse. So if you do everything perfectly, you might cut the voltage drop in half (and reduce it further by moving to thicker wire), but you're getting into the realm of diminishing returns here.

I'll measure resistance with and without load and to both sides. If I can regain something around the 0.5v ballpark I'd consider the problem fixed. I am definitely not aiming for 0.1v drops or anything unrealistic like that. My car has an old-school contact point voltage regulator which sometimes peaks briefly in the 15's so I would burn my H4s in days without any voltage drop at all.

On that note, I bought one of these to remove that awful stock regulator too: https://www.wagneralt.com/products/W095-06.asp
 

LEDphile

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I'll measure resistance with and without load and to both sides. If I can regain something around the 0.5v ballpark I'd consider the problem fixed. I am definitely not aiming for 0.1v drops or anything unrealistic like that. My car has an old-school contact point voltage regulator which sometimes peaks briefly in the 15's so I would burn my H4s in days without any voltage drop at all.
Note that when trying to measure milliohm resistances accurately, that your measurement setup makes a difference. The resistance of your test leads, and of the contact between your test probes and the device you are testing, is not inconsequential.
 

crdiscoverer

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I'll keep it in mind, thanks. As long as I keep my testing consistent, I'm more interested in resistance reductions than the actual values I get.
Like weighting yourself after Xmas, as long as you're using the same scale, you'll know you're putting up some weight :)
 

ButchW

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I'm watching this post, as, I too, will be adding a relay kit to my 1986 Suzuki Samurai... The Suzuki's, like a few other cars have a negative switching system that won't work with some newer lighting technologies ... Plus, I would like to cut down the voltage losses thru the old wiring system as well...
Butch
 

crdiscoverer

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Alright, I removed almost 2 meters of excess wire. 90cm from wire going to the battery terminals and another 90cm to the far side headlight. There are still about 50cm extra to the relays, but as LEDphile said, that's getting into diminishing returns. In the process I basically destroyed the H4 female plug because I'm an idiot. I thought it'd have been easier and add less resistance to pull out the leads from the plug and rewire them, instead of simply trimming a section in the middle. It took me almost all night to resolder the leads, make them fit, etc. So unless you have brand new plugs at hand, just trim the wire, solder, shrink tubing, done.

I'll report back soon with the new values. Might be better, might be worse.
 

crdiscoverer

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New values:

Positive drop = 0.608
Ground drop = 0.273
New total = 0.881

So I gained 0.22 volts by removing 2 meters of wire and spending almost a whole night battling an H4 plug. Granted, I probably added resistance by making new connections but it was offset by the wire removed. At 2000rpm and no other electrical load but lights, the far-side bulb is getting 13.6 volts which I consider an acceptable compromise of output vs life. The closest bulb is surely getting slightly more volts and slightly less drop, maybe 0.6v or so, I didn't measure it. What I did measure was resistance before and after removing excess length and I got about half, so I was initially hopeful I'd get better results, but I checked resistance with the relay kit off the car and no load and heat clearly plays a role.

Was it worth it? Absolutely not, don't do it. I had a chance to look more closely at the wire and it says 1.25, which I'm assuming is its gauge in mm. That's between 16 and 17 AWG. I'm a bit disappointed because from what you read on forums, etc. you expect a good relay kit to get you around 0.5v drop at most (some people even say 0.1v should be the max drop allowed). Still, I successfully went into decimals and I'll leave it like that.

Takeaways:
- If possible go for a 16AWG relay kit. That way you don't have to care so much about wire length. 18AWG will have you pruning bits of wire here and there for minimal gains.
- Don't go mess around with terminals, plugs, relay bases, etc., unless you have new replacements at hand just in case you break something. Time vs effort, it's better to simply cut wire, especially if you know how to make a good connection and can solder.
 
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ButchW

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The distance from battery/alternator to relays, to lights is not that far... Why not just go to 10 AWG or so?... Cost would be minimal....
Butch
 

crdiscoverer

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Nobody makes them. If you're patient you can build your own relay kit with different gauges for different things. 3 sleeved 10AWG wires are probably too stiff and cumbersome to route through most factory places, so that's a factor too. I think 14AWG is more than sufficient. There are calculators online which you can check to see that after 16 or so, gains are minimal since headlights don't draw that much current.
 

John_Galt

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14ga was what I built the first relay harness for my 4runner with. Unfortunately, me being an idiot, I built a positive switched harness for a negative switched system, but it did "work" "correctly" and netted me a nice 1.8v boost from the stock 22/24ga harness. I then opted for a switched ground harness from a good online vendor, and it offered 12ga wiring. I was seeing nearly charging voltage at 2k rpm at my passenger side headlamp (opposite the alternator and battery placement in the 3rd gen 4runners) which was fantastic.

I'd agree with crdiscoverer that 10ga is probably well into diminished returns for anything short of an old VW, with the battery and engine at tye opposite end of the vehicle from the headlamps. Routing and finangling through most firewalls and engine compartments is hard enough with good 12ga or 14ga wiring.
 

ButchW

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14ga was what I built the first relay harness for my 4runner with. Unfortunately, me being an idiot, I built a positive switched harness for a negative switched system, but it did "work" "correctly" and netted me a nice 1.8v boost from the stock 22/24ga harness. I then opted for a switched ground harness from a good online vendor, and it offered 12ga wiring. I was seeing nearly charging voltage at 2k rpm at my passenger side headlamp (opposite the alternator and battery placement in the 3rd gen 4runners) which was fantastic.

I'd agree with crdiscoverer that 10ga is probably well into diminished returns for anything short of an old VW, with the battery and engine at tye opposite end of the vehicle from the headlamps. Routing and finangling through most firewalls and engine compartments is hard enough with good 12ga or 14ga wiring.
Do mind passing along a link to the vendor you bought the harness from?.. I would think that the only routing of the heavier guage wire would be in the engine compartment (presuming you have a front engine car and battery)... The existing wiring to the switch should be efficient, no? The only load on it would be whatever the relays required to operate... In my little Samurai it should be a pretty simple job..
Butch
 

crdiscoverer

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I haven't seen anything thicker than 16AWG made specifically for H4 bulbs. Your best bet is getting an off-road relay kit for LED bars and auxiliary lights and adapting it to work with H4. I've seen up to 12AWG. Here is one:


You could get 2 of those kits, 1 male and 2 female H4 plugs and with a bit of work make your own H4 relay kit on steroids. The problem I see with that is that you're paying a lot more just for partially assembled wiring and questionable quality relays. You'll have to switch to a lower rating fuse and won't have any use for the switches either. At some point you have to consider if it's better just getting everything yourself and build it from scratch. It's not that difficult, just time consuming. With the royal PITA I went through trying to fit the leads back into the H4 plug, I can already imagine the nightmare it would be to do that with 12 or 10AWG.

I'm actually very surprised there are no quality H4 kits. I'm assuming the Koito one I got was just a full kit with the headlights as I can't find it for sale individually. There's nothing from Morimoto, Bosch, Denso, etc. Only cheap "cat-walking-on-keyboard" random name brands off Amazon and eBay. Presented with only that choice, I would definitely build my own.
 
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John_Galt

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Do mind passing along a link to the vendor you bought the harness from?.. I would think that the only routing of the heavier guage wire would be in the engine compartment (presuming you have a front engine car and battery)... The existing wiring to the switch should be efficient, no? The only load on it would be whatever the relays required to operate... In my little Samurai it should be a pretty simple job..
Butch

Headlight services http://headlightservices.com/

I asked for his base harness to be modified with another relay to trigger off the highbeam for my driving lights. Made for a much nicer package, and I just needed to run a pair of lines for the aux. Switch and then tie my driving lights in.

Dan Stern also builds and sells relay harnesses for vehicles, as well as other modules (gotta get the plug in).
 

ButchW

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Headlight services http://headlightservices.com/

I asked for his base harness to be modified with another relay to trigger off the highbeam for my driving lights. Made for a much nicer package, and I just needed to run a pair of lines for the aux. Switch and then tie my driving lights in.

Dan Stern also builds and sells relay harnesses for vehicles, as well as other modules (gotta get the plug in).
Thank you...
Butch
 

Sadden

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The distance from battery/alternator to relays, to lights is not that far... Why not just go to 10 AWG or so?... Cost would be minimal....
Butch
I do this on my highbeams. 9011 getting fed 10g right off the alternator are absolutely bananas.
 

Hilldweller

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Ray built me a 12 gauge harness to custom length for my Jeep, back in the day.
I had a pair of Cibie Z-beams that I got from Dan Stern and it worked great.
I later used the same harness when I started doing the first tests of JW Speaker & Trucklite LED 7" replacements. The harness obviated the need for a "flicker-kicker" adapter.
...but Trucklite made one anyhow...
 
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