The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by Crazy Steve, Nov 5, 2013.
A 2 amp fuse should be more than enough....
Serious question, what is the word in front of your ride in the "Kwik Wire" link? If they can't spell, the line drawing jumble is totally useless. Bob
I think it's Electrify Your Ride, but the bottom half of the F and the Y are cut off because of how the font is placed inside that frame.
I'd go out and look at my manual, except I'm too freakin' lazy. The manual is actually quite good.
That works! Thank you, I wouldn't ever use that company far too much wire for anything I'd ever own. Bob
Steve, charging circuit question for you. I have a 140 amp alternator and a trunk mounted battery. I am using a maxi fuse near the starter.
I will have a cable running from the battery to the starter, then a cable to the unfused side of the maxi fuse from the starter. I will have another cable from the alternator to the unfused side of the maxi fuse. That will complete the charging circuit.
The fused side of the maxi fuse will go to the panel.
For the almost 20 foot length for the charging circuit the wire calculator calls for a 0 gauge cable.
Is that the correct way to measure the cable length, or do I measure each side to the maxifuse? If I measure to the fuse, I could then use a #4 from the alternator and then a 1/0 for the battery to the starter. Somewhere when I read the 101 document, I picked up that the distance is to the starter from each end, not the total.
Sounds to me like you already are planning a 1/0 wire from the starter to battery, so you don't need to make that any larger. The wire from the alternator to the starter is pretty short, so it probably could be #4.
You're trying to minimize the voltage drop in the charging circuit, aren't you?
Minimize drop, and make sure I don't melt down. Also, the smaller wire is easier to route from the alt to the starter.
Be careful with the wiring installation. That's the most important thing.
Thanks Jim, not my first rodeo, but the biggest alternator I have ever used. Also a few more electronics than my other rides. I figure I will have the wiring in for next Christmas at the rate I seem to get things done nowdays.
You have three loads you need to calculate. One, the actual starter load from the battery to the starter, two, the total continuous loads at the fuse panel or panels plus the one largest non-continuous load, and three, the alternator output to the first connecting point. So while these three wires are connected together at a common point, they don't have the exact same load. So for the starter cable, figure a 'typical' 250 amp load for a V8 starter. If it's a high-compression big block, a blower motor, or anything that may be tougher to turn over, I'd add 50 more amps to be safe. A 1/0 cable should be adequate for this at 250 amps with sufficient 'headroom' to cover hard or hot start issues. This is assuming a ground return through the frame, and good bonding between the frame and engine, body, etc. The ground/bonding cables at the battery and starter should be the same size as the positive cable.
For load two, add your continuous loads plus the largest non-continuous or intermittent load. The continuous loads should be anything that can be operated full-time while the car is being driven; headlights/taillights, ignition, radio, wipers, heater/AC, charging station, cooling fans, fuel pumps, etc. Intermittent loads are power windows/seats, turn/brake lights, maybe compressors for air bags, etc. By ignoring all but one intermittent load, you can reduce this load. Adding just the largest intermittent load will give you 'room' to operate any 'extra' load for the brief period needed without impacting voltage to rest of the system, or at least by little enough to not be noticeable.
Load three, the alternator to fuse connection, is for practical purposes the same as load two. Again, this represents the power needed going down the road full time, so for the majority of time the car is running this load will be the same. The exception is right after starting when the alternator increases output to replace the power used when starting which will go directly to the battery. So I would figure this wire size twice; first with load two (and shooting for a 2% max drop in that length), then with the anticipated load after starting. If voltage drop doesn't exceed about 7% while charging heavy in that length, I'd consider that acceptable. Generally, the alternator will drop that extra load in a few minutes so the impact will be temporary. This can be a bit of a judgement call depending on how much difference there is between the two loads. The jumper between the fuse and the starter should be at least the same size as the alternator-to-fuse size.
Lastly, that maxifuse. I don't like these even a little bit, as they're almost never installed right in this application. Fuses are overcurrent protection devices first, overload protection second, and catastrophic short circuit protection last. Most installs I see have the last but none of the former while giving you a false sense of security. Here's the problem... So you sized the wire to the fuse panel big enough so as not have excessive voltage drop. So for an example, lets say the calculated load is 80 amps and the length of the wire is 5 feet (if you're using multiple small wires, using a single large fuse is an invitation to a fire), a #8 wire would give under 2% drop so should be fine. Fuse size is 125% of connected load, so you need a 100 amp fuse.... or is that big enough? Remember, you still have the capability of running more than one of those intermittent loads, if only by accident. Fuses are stupid; if it's designed to blow 10 milliseconds after current hits 98 amps, it won't care if you only bumped that switch for 15 milliseconds, you'll be on the side of the road with a blown fuse. So to prevent nuisance tripping, you bump the fuse size. Add 20 amps, now we're at a 120 amp fuse. That's 150% of the connected load. Far enough over that under the right conditions, that big fuse can keep that circuit running while something burns. This is the downside to using 'diversity' to reduce wire sizes; it makes installing proper protection harder. Truthfully, the only thing that fuse is protecting is the wire from the fuse to the fuse panels and the panel buss, and only against catastrophic short circuit. That can be addressed with careful routing and protection from damage. For actual overcurrent and overload protection, you have to look at circuit breakers or fusible links. A circuit breaker would be my choice (in this size, a non-auto-reset version would probably be best), I'd look for a 90 amp breaker. These will clear a short nearly as quickly as a fuse, and are generally forgiving of intermittent overloads of short duration. The fusible link offer similar protection, but can't be reset and the lack of info on circuit clear times and current slopes makes picking one very difficult.
Steve, I found the following from Del City. They are flat and waterproof. I would hook them the same as the Maxi Fuse correct? I will keep looking, I would rather have one in an enclosed case that the posts are not in the open. This is the type of breaker you are talking about, correct?
Hi-Amp Surface Mount Circuit Breakers - 1/4" Stud Manual Reset (Switchable) Part # 76610
Look at audio stuff rather than the Del City ; I have found the 1/4" studs to be too small and provide less contact surface than audio components. A Rockford-Fosgate 100amp circuit breaker has 3/8" studs and provides a greater contact area. If you're really worried (amp-wise) you can probably find a 150 or 200 amp breaker, or run 2 x 100 in parallel. I found the Rockford one at < ceautoelectricsupply.com >.
Thanks Vic, That was kind of what I was looking for with the wires enclosed. One of the problems with living here in Helena is there's but only one stereo shop in town, and it is quite limited. Can't just walk in a look at stuff.
We use Bussmann Hi Amp breakers on our high school robots, #6 wire, 120 amp CB185-120, they have a button to turn it off, as well as turn it back on.
Maybe the same breaker, but less money, made by Buss, and has tech specs.... http://www.connectorconcepts.com/hicibr90amma.html
Has a wide enough current slope to handle a 25% overload for minutes, but will clear larger ones quicker so you don't have to oversize it. A 1/4" stud with the proper connector will easily carry 100 amps. I'm not saying this is the size you need, you still need to calculate the load. Too big, and you might as well leave the maxifuse.
There's these marine units; larger studs... http://www.connectorconcepts.com/maracibr100a.html
A bit more money, but still less than Del City.
The Rockford-Fosgate looks like overkill to me... and you're limited to three wire sizes it appears.
This is the best electrical thread I've seen. Been learning a lot. One thing I've been wondering about is in post #176.
I understand using a #4 wire from the 12v power point to the relay in diagram 4. It feeds both fuse panels. The relay is also rated for the 88.5 amp total of both panels. The relay only feeds the switched panel, as far as I can tell. Could it be rated lower to the total of just the switched panel ? Maybe I am missing something.
Actually, that's a good question, and I should have clarified this better. Yes, you can rate the relay for just the connected load, BUT you do have to pay attention to TOTAL load, not just the 'calculated' load when motor loads are involved. While wire and connections can withstand short-duration overloads, switch/relay contacts need to be rated for the MAXIMUM current that will be seen, not the derated amount. Failure to do this will lead to shortened switch/relay contact life.
So if you go back to post #75, you'll see that my example has a total continuous load of 53 amps on the switched fuse panel, but the TOTAL load is actually 92 amps. And that's not including the inrush current spikes the relay will see when any motor load starts, which can be as much as 1200% of the running current instantaneously. Typically, 300% over the running current will be present in measurable amounts while starting. So let's do the math...
Let's say the last time you ran the car, you had all the switched continuous loads on when you turned the car off. The relay disconnects all power, so you don't need to turn off the individual items. When you next turn the key on, all those loads come on at once. So you have 53 amps applied to the relay. Or do you? You have two motor loads (the wipers and heat/AC), these will have inrush current spikes until they reach full speed. The example has these fused at 6 and 24 amps, and because the fuse size is 125% of the running current, the actual load is 24 amps (6 + 24 = 30, 30 X .8 = 24 amps). Multiply that 24 amps by 300% (24 X 3 = 72 amps), and your momentary load on the relay is 95 amps (72 + 12 + 4 + 7 = 95). A 100 amp relay will be perfect for long contact life.
Generally, if you size the relay to the total connected load with no derating or diversity, you'll be close enough. But if you have a lot of motor loads (let's say in addition to what my example has, you also have an electric fuel pump and air compressor for airbags that could come when turning the key on), it would probably be a good idea to calculate this to insure the relay rating is high enough. Ideally, the relay should be rated for 100% or more of the maximum load, but in cases where it's unlikely that all the loads will be on at once, if you can reach 90% I would consider that acceptable.
One thing to remember is that ALL loads have inrush current, but for non-motor loads they're generally small enough and of a short enough duration that they can be ignored for our purposes.
Is there any downside to using relays rated way above the load?
NO, but no advantage that I can see.
Just thinkin' that someone might have a larger relay in their spare parts bin that could be used instead of going to town to get the "more appropriately sized" one.
OR; someone that doesn't know or understand how to calculate the appropriate size might just use gihugie ones everywhere just to be safe.
Thank you for the reply, Steve. I've got a handle on it now. My loads are smaller, which makes it easier.
Steve can you or anyone else review the diagram here and explain the "jumper wire to ground" on the regulator? It doesn't seem right to me.
That's a 'test' jumper. If your charging system isn't working and you don't know which part is bad (alt/reg), hooking this jumper up bypasses the regulator. If the regulator is bad, it will not be showing output without the jumper. The jumper is not for normal operation.
It might be on here and I missed it but how do most of y'all connect wires. After a buddy laughed at my work he showed me how he solders the wires.
Sent from my iPhone using H.A.M.B.
I crimp a lot of things. I have a good variety of crimp tools, I make good crimps and leave enough extra wire for strain relief. The wire is never under tension once it gets installed. Any crimp connection under the hood gets shrink sleeve over it, I use one that has the adhesive inside of it pretty often.
The regulator must be grounded to work properly. It can be grounded by bolting it to the firewall.
In that (70 and up Mopar) system, there are two connections to the alternator field. + voltage to one side and -voltage to the other. In that setup, the regulator controls the -voltage, energizing the field so the alternator increases its output.
In a 69 and down system, there's only one field connection. That is a +voltage and the field is grounded internally. The regulator controls +voltage, energizing the field etc.
You can use a 70 and up alternator with an earlier regulator by grounding one of the field connections, but you can't use a 69 and down alternator with a 70 and up regulator.
Thanks Big John.
Next question: If I use 12 gauge wire from the ignition switch to the starter, do I really need the relay? What would that diagram look like?
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