Technical Relays, Fuses and Circuit Breakers

Here's another 4 relays in a box arrangement, 30A each.
https://watsons-streetworks.com/?gc...yYuQ2WOb4mGlg2Caapx5UWimEzjsGVZMaAiHjEALw_wcB

 

@Crazy Steve , this is the relay/socket package I have used
https://watsons-streetworks.com/pro...-ignition-switch-relief-relay-accessory-feed/

Here is the application where I have used these relays:
https://watsons-streetworks.com/a-current-topic/

 

The MSD relays are solid state, so no mechanical contacts, which could improve reliability. Not that the Bosch relays are unreliable, but SS just takes that reliability 1 step further. And it is a cleaner installation was well.

 

The problem I see with something like this is if 1 relay fails (and the other 3 are all being used) you have to replace the entire unit, not just 1 relay. It looks like it still uses mechanical contacts unlike the MSD solid state relays, so other then a slightly cleaner look I don't see a real benefit vs individual cube style relays.

 

Well... First let me say that I'm very conservative in my circuit designs. I'll apply any and all derate factors to ensure long life, something the automotive aftermarket rarely does. One thing they never mention is any current-switching device should be derated to 80% for safety and reliability reasons. Exposing them to 100% load for extended time will shorten their service life, sometimes catastrophically. For me, safety is king, reliability is 2, serviceability is 3, cost is 4, and convenience while important is last. With that said, here's my opinion on these high-current and 'modular' relays...

@pprather , my original reservations about this relay haven't changed. They're furnishing it with #10 leads and terminals which are only rated at 30 amps. Now, I'll admit that it will probably work 99% of the time, but that 1% could burn your car down. When using one of these, keep your circuit wire lengths to a minimum, I wouldn't go any more than 8 feet total. And there's a better solution available (for less money); McMaster-Carr offers a 100 amp continuous rated relay for about $25, part # 7995K41. For $20 more, you can get a 200 amp rated relay, part # 7995K31. Both feature all bolted connections. Now, McMaster-Carr does sell this type of plug-in relay (for considerably less) but because they sell to industrial/commercial customers who don't want to worry about excess failures they more-correctly identify these as high starting current relays. They offer a 50 amp version (part # 9672K36) for less $ but do tell you the maximum switching current.

Those 'modular' relay assemblies appear to me as a solution looking for a problem. As @Blues4U correctly points out, any failure will require replacing the entire module. I will give MSD credit for at least laying out the current limitations of theirs, but that info to most end-users with their limited knowledge on how to configure the system won't be all that helpful. One miscalculation and you're out a $170 module. The Watsons module has mostly the same issues, just a lower price. And neither is plug-and-play, so replacing either will be a chore. The only possible attraction for me would be in a case of extreme space constraints, and it doesn't look like you'd save that much. And being proprietary parts, any failures mean you're broke down until you get a replacement from the original manufacturer. Personally, I don't think these will be all that popular and in a few years will probably be discontinued, then what? You can get Bosch-style relays almost everywhere...

Relays have very legitimate uses, but far too often the aftermarket uses them to 'fix' inadequacies in their basic harness designs. Even the OEMs do this, but for them it's a cost-saving measure, and generally done to limit required inventory. The only excuse I see for the aftermarket is price competition. And it never ceases to amaze me how a builder will spend whatever amount of money it takes on the rest of the car then buy the lowest-cost harness purported to be correct for their application. I have yet to see an aftermarket harness that I would personally buy for anything other than a very 'basic' car.

Truth be told, most cars don't need relays or very few if the basic harness is built right. A 'basic' car with 'standard' accessories like radio, heater, turn signals and horn, you may need one relay for the horn. Start adding stuff like AC, power windows, electric fuel pump, air bag compressors, and cooling fans you'll have to add two; one for the switched side of the fuse panel (this is where that 100 amp relay above comes in) and one to control the fan. If you have a four headlight car and switch to high-wattage halogens, you'll need one more to feed the high beams. You'll also need to upsize the feed wire to the fuse panel (this is where the aftermarket falls down badly). I've covered most of this in my 'Wiring 101' thread. If I were 20 years younger and ambitious, I'd go into business building a quality harness, there is definitely a market out there...

 

Do you know how long I've searched for one of those rare 52 amp fuses?

 

btt

 

I wish someone would do a tech thread on rachet crimpers. I have bought 2 or 3 sets over the years, but they stay in the toolbox because I am not sure which terminals to use for what application.

 

Steve , I can identify with the relays sticking. I had two fire engines of the same brand that would “ stick” the huge relays providing current for the starters! Checked everything thing! Everything seemed to be the same as all my other fire trucks! I even send the relays into Cole-Hearse for examination. They said I had low voltage to them!After several years of replacing the relays, the starters played out. I replaced the starters with gear reduction starters and my problem when away! These sticking relays took out the Delco starters by sticking!
It wasn’t until the advent of the internet and the sharing of minds that I figured out my original problem! The wires going to the relays were longer on those two trucks than all my other engines, even though the wires were the same gauge! There was my voltage drop!
So…. relays not properly installed can cause problems! For sure!








Bones

 

Ratcheting crimpers came into existence for one reason only; to allow the terminal manufacturers to warranty the performance of the terminals they sell. When these first started showing up, they were terminal brand/type limited, precision machined, very expensive, and the better ones still are. Then the aftermarket got into the mix, changing designs enough to avoid any patent infringements and continually cheapening them to bring prices down.

Yeah, I've got a couple I never use too. I don't use them because I know I can get a 100% crimp every time with barrel terminals and my trusty T&B WT111 hand crimper. I've got hydraulic for the larger sizes. But ratchet crimpers? Unless they're UL-approved for the specific terminal your using, you may or may not get a good crimp. Where they're popular in industrial/commercial applications is in low-voltage applications with current limiting where life-safety is a very low priority because the systems are 'intrinsically safe'.

The problem with automotive applications is no one is watching; UL doesn't care, the OEMs only care if the stock harness functions without warranty issues. In spite of the problems they've had and lawsuits that ensued (GM ignition switches that failed to power airbags, runaway Toyotas, various Tesla issues to name a few), no external body has stepped up to actually police them, and that's the OEMs. There's even less in the aftermarket. Where approval exists, it's for specific uses and automotive isn't one of them.

 

And this is why I hammer on doing voltage drop calculations. At 12 volts, wire length gets important quickly. At 120V or higher voltages, a few volts dropped won't be noticed as a percentage, but will show up fast at 12. The thing to remember is for a given wire size/length, the amount of voltage drop is controlled by the circuit current, system voltage has nothing to do with it. Lose two volts at 120V, you're still at 98% of system voltage. Lose the same two volts in a 12V system, you're down to 83%. The higher the circuit current, the faster this shows up.

And motor circuits is where it really shows up. Unlike resistive circuits where if voltage drops the circuit just doesn't work as well (think dim lights), reduce voltage to a motor and it'll draw more current to perform the same work. Sometimes a lot more.... and more current increases the drop, starting a circle leading to possible destruction/fire.

 

Funny, I have a version of those crimpers from 1950 or so. That's what I always use, I just figured the new ratcheting type were more accurate.

 

They were basically designed to make the process as idiot-proof as possible. There are some terminals that require the special crimper, I've got one for installing terminals onto plastic film ceiling heating panels.

 

https://www.knipex.com/products/cri...icrimpcrimping-pliers-changer-magazine/973302

 

Thanks for this. I just ordered a vintage one on the auction site for a reasonable price.

 

And here's how to use it.... https://www.jalopyjournal.com/forum/threads/crimping-tutorial.1127519/

 

Here’s something I’ve been working on. Just plug and play. All the hard work has been done for you. Technology is a great sometimes, right?

https://www.jalopyjournal.com/forum/threads/four-channel-power-switch-hot-rod.1246721/

 

Great article by Hot Rod on this. Very much worth the read.

https://www.motortrend.com/how-to/what-size-electrical-wire-should-i-run/

 

Every time you post some electrical explanation, I learn something. You certainly know your "s**t". Thanks for sharing this esoteric knowledge.............

Edit add:

A relay is nothing more than an electrically-operated switch. It has NO overcurrent protection.


So would you fuse/breaker the wire to the relay, the wire to the component, or both?

 

That's one of the few 'hot rod electrical' articles I've seen with actual accurate information and good advice. The only fault I'll find with it is they're doing the calculation the old-fashioned way which can get a bit tedious. There's web-based calculators that will make this much easier (no pesky math involved), this is the one I like... Voltage Drop Calculator . Note there's three choices; NEC, estimated, and other. Use the 'estimated' calculator and simply plug in the requested data. Make sure you select 'DC' and the one fly in the ointment is wire length is assumed to be both ways, if you're using a chassis ground enter 1/2 of the wire length to get an accurate result. If it's a fiberglass car with separate grounds then you wouldn't do that. I would include any ground tails if used if they are of any length (1' or longer). The key thing to remember is voltage drops are additive. If you lose 2% between point A and point B, everything after B is already down that 2%. I don't like seeing any more than a 5% total drop below battery/charging system output anywhere.

There are other factors that can help determine wire size including continuous and intermittent loads and diversity. For a fuller explanation of these look here... Wiring 101 | The H.A.M.B. (jalopyjournal.com)

Any fuse should be installed at the circuit point of origin, usually the fuse panel, and that is usually all you'll need for proper protection. There can be a handful of exceptions.

Several are how you operate the relay coil. These can be wired three different ways (each with advantages/disadvantages). The first way is to pull your control power off the circuit power coming into the relay. You now have two choices in how you control it; you can wire the power directly to the coil and use a remote switch that simply grounds the other side (AKA one wire control). This is typically how horn relays are wired, but if that ground shorts you no longer have control. Second way is take that wire to a switch then return, but the wire either has to be the same size as the main circuit wire for overcurrent protection or you can install a small value in-line fuse at the relay and reduce the wire size. Third choice is to use a totally separate control circuit, which is how nearly all starter solenoids/relays are factory wired. One circuit can power multiple relays.

The other exception would be if you're operating multiple devices off the same relay. If you have a large current input and wish to reduce wire size after the relay to the individual devices, you may want to install fuses.
This isn't a hard and fast rule, it depends on what's hooked up and how the device fails. As an example, taking a 20 amp fused #12 wire to the headlights, you could drop to a #14 after you leave the first one as load will drop by half and I wouldn't worry about it. But with a 30 amp circuit connected to three 8 amp motor loads, those I'd fuse if dropping wire size.

 

I'll add one caveat to the above. If fuses after the relay are needed/desired, I'd probably use manual reset circuit breakers. Manual reset so if there is a problem I'll be aware of it, and less likely to have a random failure which can occur with fuses. Plus there won't be fuses scattered about....

 

I use fuses all the time. relays some times on lights or electric fans.

More often than not I do not have a fuse panel so I use inline fuses.

I also have been known to use a fusible link on my main power wire. most of the fellas here do not do that. I am not sure how important that is for safety but it worked for GM. LOL

 

I got a relay board from Leash Electronics to make wiring a little easier. One hot from the battery and a ground from the battery. Fuse it to the amperage you need for what you are running.

 

My LSR roadster does not have one fuse or relay. I use an electric water pump, fuel pump, and ignition. I’ve taken my chances since 1975, never ever had a problem, and I’ll stay that way thank you very much.

 

My 1954 Chrysler does not have a fuse from battery to bat terminal on the voltage regulator. Most of all cars with generator were like this. All is good except when the cutout relay gets stuck. The generator will try to motor and will quickly run the battery down, but there is no protection for this. In this case I would be inclined to use a high current relay in between the battery and regulator that is energized only when ignition is on.

 

How do you like this one?

 

It worked out really well and I would use this setup again. Relays and fuses are in one spot. Don’t have to hide them in some out of the way place. The board is really well built.

 

so cool! Great to hear that

 

Used relays for my hi beam/lo beam headlights on my (M-word) hot rod and never realized how dim the factory set-up was!
Also got tired of new(er) halogen headlights tripping the breaker in my headlight switch while going 70 mph down a dark country road.. Eventually(once the breaker cooled off) they would come back on...only to go off again a few minutes later!!
Very exciting in a sick kinda way..........
6sally6