What in the ....?????? Low voltage reading, yet full battery and alternator working.

Topic: What in the ....?????? Low voltage reading, yet full battery and alternator working. (Read 19616 times) previous topic - next topic

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #75 – June 28, 2014, 08:11:49 AM

Quote from: Haystack;435250

It really is simple math and they have a standard chart to look up.

his alt puts out 158 amps at 13.8's if i remeber right. on a dead battery it is likely the alt when stressed will only put ut a bit over 12v's. that's what i suggested what i did. voltage x amps = watts. 2180 watts. divide that by 12.5 and you get 174 amps. that is the minimum id put in there if it was me.

the 4 guage wire is rated for 150-200 amps assuming the wiring length is 47ft.

Quote from: Haystack;435250

It really is simple math and they have a standard chart to look up.

his alt puts out 158 amps at 13.8's if i remeber right. on a dead battery it is likely the alt when stressed will only put ut a bit over 12v's. that's what i suggested what i did. voltage x amps = watts. 2180 watts. divide that by 12.5 and you get 174 amps. that is the minimum id put in there if it was me.

the 4 guage wire is rated for 150-200 amps assuming the wiring length is 47ft.

looks like someone gets it!

to calculate a wire size based on an engineered VOLTAGE DROP................. 11.1 x LL x A / VD
11.1 k factor constant for copper (can use 10.

x loop lenght x full or 80% breaker rating / voltage drop (your desired allowable voltage drop.
*loop footage includes the hot wire distance plus the individual piece of equipments associated ground wire lenght. this is important to consider voltage drop so add up the "full circuit loop length"

google this phrase "NEC conductor properties table" and use the "CIR MILLS" column.

i wont use 47 ft as the distance,, since i know the application and its the alt wiring to solenoid, Ill use 8ft for the hot wire plus i will use 4ft for the existing battery ground return cable to the engine block ,, which equals 12ft loop

I will only use .2vd for my "allowable voltage drop"
I believe .2v is very high though for a low voltage application of nominal 14.4vdc source but in cars thats what ive been told is acceptable.

11.1 x 12Loop feet x 150Amps / .2 ( i am allowing for 2 tenths of a volt drop (vd) )

this comes to 99900 circulair mills of copper required to cover the design.
refer to the conductor properties table and you will find 99900 is larger than #1awg but less than 1/o. use 1/o wire rhh/rhw flex

to calculate a wire size based on wire you have available to determine what the voltage drop will be.................

lets assume you have 4awg lying around...... the conductor properties table tell us 4awg is 41740 cir mills of copper
using the same formula as above except substituting the wire you have available in place of the desired voltage drop...........
11.1 x 12loop feet x 150A / 41740 = .4787 volts drop.

in both cases above you can derate to 80% of your amperage be it your device being powered or your over current protection.

you wont find this formula in the NEC, cars are exempt from compliance to it. the nec still doesnt have a friggin clue on low voltage dc wire size calculations. I have schooled Mike Holts forums a couple times on this.. they are slowly coming around though.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #76 – June 28, 2014, 01:12:21 PM

I have no idea what anything after you quoting my post means...

all i know is running model airplane stuff I've ran over 50 amps at 12v's through a single 12 guage wire. the wires are 3" long on battery and esc. i added a 1' length of 10 guage for a 30 amp setup and it would get hot. in sure a 6 guage would be plenty and i'd wire it straight to the battery using.less then 4ft of wire, which should allow tou to run a full 200amps through the wire.

id also upgrade the ground.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #77 – June 28, 2014, 01:52:54 PM

Quote

id also upgrade the ground.

The negative battery ground? I already have the parts in hand for that. The one for the starter as well.
Engine block straps are done. Gotta get to that one in the trans tunnel. Of course it's routed on the driver side where I can't get in there without jacking the car what with all the linkage stuff for the AOD in the way. I wither need a 3rd arm or another elbow on each of the arms I already have.

Scott was paying you a compliment.

Tom, the links have done their job and I understand the reasoning behind them as opposed to a simple fuse. Once it goes it's not so easy to set and forget.
Still, if a fuse DOES let go, I'm not the average guy to just reset it. Hence all the questions here. Once this is wired in I want peace of mind as well as ease of future maintenance.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #78 – June 28, 2014, 07:44:27 PM

First off cars are DC not AC and have a reduced current factor as it recovers from start up..So a 100% wire factor is never used in alternator wiring as far as charging leads go. Secondly an automotive alternator can only put out it's max current for one minute by design, Third is the fact that the alternator sees a reduced load as the vehicles battery begins to recover its initial discharge . It normally takes 10-15 minutes from a start mode. So basically an alternator never sees anywhere near half it's load capacity. And normally 1/4 of its max load rating. And lets for example say it does. Using a 140 amp alternator you would be using half lets say at 70 amps and that is where the alternator would sit for 10-20 minutes and fall off after the battery recovers. So i am going on record as saying a number 8-10 AWG is where it should be at or around 10 feet on a 140 Amp alternator. And over the years using my SUN VAT i have seen hundreds of cars running with close to 100% load and not topping off a current draw anywhere near 40 Amps total after battery recovery. Just me and that is from experience. years back cars had generators that in a good day could put out 35 amps and cars ran perfectly and battery's were not undercharged. But today those loads are higher of course but the need to gauge a wire on 100% capacity is not how it is done on cars. Reason being the load is always tapering off after a cold start lets say. Also the wire lengths are very short distances as well. For example an alternator wire is never more than app 6 feet to the load the battery and the ground wire is not more than lets say 2 feet at best. But people are wiring alternators with 2 gauge wire. Totally overkill in my view and not necessary. Nothing wrong with big wire but fusing has to be appropriate. Once again would you wire you outlets with 6 gauge wire and fuse them for 40 AMPS. I don't think so. So looking at the wire size of many a cars and trucks over the years i have never seen a main feed alternator bigger than 8 AWG. Now in over the road trucks it is different. You are dealing with multiple batterys in parallel and sometimes 4-5 in certain vehicles. That takes big wire but normally those alternators are quite big. reason being recovering a cold start from a large diesel truck is high current draws. But then again it tapers off as the battery's recovers. have a good weekend guys.

His alternator will never put out 158 amps.
Powermaster recommends a number 6 AWG for wiring for applications of 10 Feet for a 150 Amp output alternator.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #79 – June 28, 2014, 11:57:40 PM

Guess there is no reason to upgrade then.

ac wiring is litterly 10 times the voltage. minimum of 120v's. a ten amp fuse on ac is ove 1200watts. your microwave or a hair drier are about the only thing in your house that could blow that, but ac is completely different as far as power goes. you will NEVER see 00 guage wire in a house unless it has its own transformer sub station.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #80 – June 29, 2014, 06:29:30 AM

Stacks what you and others do not understand is an automotive Alternator is not putting out it's full power constantly. jay is figuring wire ampacity at constant load and full load. Where an automobile never runs like that. I am not saying bigger wire is NG what i am saying is in my career i have never seen a car factory stock with a number 2 Gauge wire run from the alternator to the battery. I have seen giant fuses like some Fords with 175 Amp fuses. Why Ford did this i have no clue and it amazes me as the biggest alternator option is 140A. Can you please find a factory stock car with a number 2 feed cable from the factory and post a photo of it. Thanks have a good Sunday Guys.

Example years back cars had generators and they barely were able to put out 35 amps . They ran and started perfectly. And those old gigantic engines were hard to crank. So how much more power does a new car use compared to an older car? 15 More amps maybe. have you ever installed a new alternator in a car? It clearly says do not install it until you charge the battery. It clearly says do not use the new alternator as a battery charger. Reason being in some cases the alternator will burn out if allowed to put out high current to recover a dead battery. Normally this is not an issue as i have jumped started hundreds of stone dead batterys in my career but alternator rebuilder's still claim they can not recover a dead battery and will fail. It is always better to have the reserve capacity of a big alternator no question on that. But another factor is how fast an alternator turns as to it's ability to produce output. Normally 15000 RPM is where an alternator will produce max output. The GM DURAMAX has a 105 AMP alternator from the factory and has absolutely no problem charging 2 batterys and supply enough power to power up a trailer with lights and electric brakes run a snow plow with no issues whatsoever. Now Fords come with a 140 AMP alternator and can barely supply enough power to run the truck let aside run accessory's like a plow ETC. Thats why they have 2 alternators from the factory. It depends on several factors stacks. And like i said i have never seen any stock car or light truck with a battery feed wire bigger than number 6 AWG from the factory. Some new er cars do and fuse fpr 175 amps. My daughters Honda does not even have a number 2 gauge from the battery. most Foreign puppiesanese cars have 4 gauge battery cables . Check it out . Good conversation Stacks have a good Sunday Guys. The Mark Lincoln uses a 175 A fuse but not a number 1 or 2 gauge feed wire. WHY??

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #81 – June 29, 2014, 09:14:47 AM

Quote from: TOM Renzo;435277

Stacks what you and others do not understand is an automotive Alternator is not putting out it's full power constantly. jay is figuring wire ampacity at constant load and full load.

yup, thats correct. .. i agree with your opinion.......... cant say i will tell someone to build a design like that without accepting the risk.
if i were to actually size the wire personally, i would clearly understand that at max output there is an undesireable amount of ac ripple. where the ripple disappears is probably at that the derated amperage that rarely is ever told to you when you buy electrical parts. All things as you know have a "max" this and that......... but you have to dig in to find the useable value.
its assumed the battery will clean up any AC ripple but then that brings in another topic of battery lifespan and damages due to it doing so.

in my stock alternator case of 65A,, im gonna call it a 65A alternator derated to 70% effeciency which is about 45A
in my stock alternator regulator , i have no clue its max vs derated engineered design but i am very sure its going to add come impedence to the alternator performance but staying at 45A should be a good baseline to design around. its really really easy to see 45A load on your car with all things on including brake lights, turn signals, high beams , radio, hvac, heated seats, hitting power windows both at once. yes i just described a real load situation that can occure.

could you ever decide that during a power ottage that you want to get AC power to your home using your new 2000w inverter? sure.
~an inverter is interesting because of those available to the general public have such huge derated values, thier lack of efficency adds more impendence on the alternator above what i am describing here.

what i do say is that i totally agree with the loads you described, yet if you dont wire to the application, then your asking for trouble.
i have trouble staying in the sand box because im over here thinking about all the crazy stuff people are capable of doing , or using thier car to do.

Quote from: TOM Renzo;435277

The Mark Lincoln uses a 175 A fuse but not a number 1 or 2 gauge feed wire. WHY??

yeah,, thats not right.
the wire shall be sized to be able to take the device load and tripping the over current protection device "before" the wire catches on fire. I suppose nec table 310.17 allows it to happen because #2 is good for about 190A at 90degC if i recall correctly.
auto co's is not req'd to comply with the NEC so they must have thier own ref tables.
insulation coating also lets wierd high amperages be allowed on smaller wire as well...

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #82 – June 29, 2014, 10:29:48 AM

Which brings up the point that my shop has 400 Amp service fed with a number 6 AWG from the telephone pole to the building. Then connects to 3/0 cable feeding the panel in the shop. This was told to me by the licensed electrition that up dated our building to 400 AMPS

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #83 – June 29, 2014, 05:39:16 PM

Considering that other than the charging system the car remains relatively unchanged WRT electrical components I wonder if even a 125 amp fuse would be overkill. Perhaps a 100 might be a better fit.....

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #84 – June 30, 2014, 08:11:48 AM

yes, your car as tom said will never ever see any current demands near that value. if you ever ever ever saw 70A i would be amazed.
yet if amplifiers or perhaps a 120v or 120/240 inverter were used like i have in the past (750w), then thats where you add in bullet proof wiring / fusing.

since i have no auto engineering experience, I have to assume and recommend nec table 310.16 "in cable tray or raceway wire ampacity ratings.
all our wires are in a loom so its not allowed to be considered "free air" if a nec table were used.

in your case, the only net gain is reducing voltage drop across the resistivity of the wire. its very beneficial because you know from now on what you read at the battery better be the same voltage you read everywhere else down in the hunderths (sp?) of volts.

i think the reasons people enjoy the 3g upgrade is that going from stock, to 3g, they experience an instant visual / audible change in thier car because they have crossed over beyond the "inefficiency" of thier previous alternator...... just my opinion though.

to go beyond a 3g means two things happened,
-1- you added RV/ camping applications to your vehicles use
-2- technologies have evolved so much that the load demands have made it so. soon to come to your new car will be such technologies either PC / Windows based or higher load demands on various car components. I actually look for the industry standard to evolve soon to 24v in cars.... seeing hints of its need already.

if the industry standard would to to a negative voltage platform (some call it a positive ground system..) then that would cure most all corrosion issues as well because your ground reference would be more positive than your voltage source. corrosion occurs during the exchange of negative electrons,, making the ground positive cures most all of this.
Example, open up your telepone NID,, ask yoursefl why those tiny 22awg wires are not all jacked up with corrosion. its because of the -48v dc plant back at the phone office. positive ground use to be the standard in cars not too long ago.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #85 – June 30, 2014, 08:21:23 AM

Quote from: TOM Renzo;435281

Which brings up the point that my shop has 400 Amp service fed with a number 6 AWG from the telephone pole to the building. Then connects to 3/0 cable feeding the panel in the shop. This was told to me by the licensed electrition that up dated our building to 400 AMPS

there is logic...
if you climb a ladder and go up to the weather head where the power comes in, using a clamp on meter read your amps on each leg...
the power co has years of trend data that shows your peak demands and that value may actually be that low.

as for your AC guy, at the very least he was/is in the rest of the nation required to at a minimum use 2) 2/0 per pole or per phase from the weatherhead all throughout the downstream path up to the terminal lugs on the 400A rated MDP (is your main dist panel board name plate rated for 400A?)

3/0 is rated for 200A in raceway or conduit per table 310.16 at 75degC, rated for 225A at 105degC.

But, if he had a drug deal with the inspector, perhaps he got a way with it.

a 6awg aerial feeder from your pole to the weather head is exempt from the nec cause the power co provided it.

i recently found out why there are exemptions to certain national infrustructure disiplines, its so that in an emergency there are no regulations to slow down the repairs and especially during a matter of national security.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #86 – June 30, 2014, 06:31:18 PM

Not 100% but the inspector said it was OK with the 3/0 to the meter and to the panel and i guess to the top of the building. But the skinny wires from the electric co kind of shocked me as the guy from the electric CO did not replace them with fatter wire. He claims that a 400A service is not a problem for the wires from the pole. He also told me if i maxed out the capacity of the wire i would not be able to pay the electric bill it would be astronomically expensive as he claims. But i needed more power and had to UP DATE. have a great evening guys. By the way the aerial as it is called i think is ALUMINUM WIRE TO BOOT. The installer said copper would be to heavy and rip out of the building in bad weather. WOW!!!

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #87 – June 30, 2014, 07:06:04 PM

All power cable is a type of alluminum for overhead use. underground they use copper.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #88 – June 30, 2014, 09:17:37 PM

yup, cheaper is the reason.
for the same amp rating in copper, you step up one size in Aluminum to be equal to copper.

tom, if its your task to get the utility upgraded, call me.. I know how to "say" the right things to get them to do it.
at the end of the day you can get what you want,, but you will pay.
so if your demands to say you need it,, "if" you want it then you must pay for it.....

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #89 – July 03, 2014, 02:23:33 PM

The car is back together.

Quote from: TheFoeYouKnow;434991

I pulled the whole cable out of the harness and ran a new one with a 175A molded in fuse that I pulled off a 3rd gen Escape. It has ring terminals on both ends and the length was just right.

This is stock Ford factory components. Those wires are 6 gauge upon investigation. 6 gauge, 175 amp, alternator rated @ 130 that'll max at about 145..... I wish I knew the reasoning behind this. I'm seeing 2 schools of thought on this throughout every web search I've done so far. Run the 200 or rock a 100/125 or so.....

Right now it has the 200 in it. The only warmth was that of the sun on my back. All is well.

I still have the old alternator. I'm going to bench test it just to see what happened. My guess? When the link blew a diode went then or shortly thereafter as well.

FWIW -- I kept the stock charging wires, pigtail and voltage regulator pigtail in the car, taped, waterproofed and out of the way. I only cut it back where the initial fusible link that gave me issues was at.

Next trick: New TB and EGR spacer, elbow, MAF....

Running a 70 mm TB and spacer with a 73 mm MAF. Will be going 75 and 76 respectively.....