Alternator Question?

[Swampdog]

I have a 65 Amp Alternator and when I fire up the engine I get 13.9 volts and it stays there till the electric fan comes on, (has 40 Amp relay). Then it drops to 12.8/12.9 volts. When I turn on the lights it drops to about 12 volts.

The engine RPM doesn't change anything. Standard pulleys and the belt is tight.

I ordered a140 Amp today.

What size wire do I need for the 140 Amp? I think I have 10 gauge right now.

Thanks

Swampdog

 

[railroad]

I have a couple of after market alternators and seems like both recommended 10 gauge. Be sure to use quality lugs on the ends.
I can see your concern with the low amp alt you now have, but it sounds like it is handling the job, unless your fan is on all the time.

 

[Swampdog]

My fan runs all the time here in the summer. I have a 180* thermostat and the fan comes on at 185*. It is suppose to kick off at 165* but with the thermostat is never gets down to that.

Swampdog

 

[railroad]

Nothing totally wrong about your thermo settings, but they are too low. You need a higher window, ie
190* on, 180* off. Depending on your type of driving, cruise speeds above 40 mph should cool the engine, no need for the fan. Not many engines cool down to 165* here in the South.

 

[Screaming Metal]

Also, if you have everything turned on, and your @ 12 volts, rev the motor a little, usually that will excite things enough get what you need. I add all my current draw up, thats lights fans, pumps then I add a 15-25% safety factor, and get the Alt. next size up....at go
Also have to remember that going too big will cause problems because of wire sizes....unless you plan on that. Make sure all your connections are good, clean, and tight. Throw some resistance in there and you could over heat some of your wires....
Watch to make sure you don't overcharge your battery also....

 

[2old2fast]

If the regulator is working properly , why would a battery "overcharge ???
dave

 

[Screaming Metal]

I've seen batterys get 13 volts from a charging system and live. Then agian I've seen a alt. go out, to be replaced by a bigger output one. At replacement of alt., voltage went up to 13.8 -14.0 volts. A steady charge of 1.8 volts over the 12 is sometimes within spec....but for the battery, it was seasoned to 13.0 volts....and started lossing water because of the higher overall charge. Just saying!
A battery has a memory. It remembers being short charged. This can sometimes shorten a batterys life if thrown a full load all the time.
Put it likk this, a trolling motor battery, if you don't run it down completely, you will get the battery used to not being fully discharged before charging.
Drain it completely everytime, then give it a good full charge, and that battery will last longer.

 

[Wild Mango]

I have a 65 Amp Alternator and when I fire up the engine I get 13.9 volts and it stays there till the electric fan comes on, (has 40 Amp relay). Then it drops to 12.8/12.9 volts. When I turn on the lights it drops to about 12 volts.

The engine RPM doesn't change anything. Standard pulleys and the belt is tight.

I ordered a140 Amp today.

What size wire do I need for the 140 Amp? I think I have 10 gauge right now.

Thanks

Swampdog

Everything seems normal here to us Auto Electricians, Swampdog. Fully charged battery shows around 13.8V at the terminals. Your fan will use about say 6A (that 40A for the relay is a current carrying rating, not a load) and around 120W of lighting load will take up say 11Amps, and lets not forget the ignition load at say 3A. Your alternator is taking up the load and because there is work going on there is volt drop, is all. I would expect the 140A alternator to behave exactly the same. A 140A (1.7kW) alternator is one big beast for a lil' ol' bucket. If you think of your electrical loads in Watts (Power) that require Volts and Amps to drive them, and Amps (Power divided by Voltage) as what dictates cable size things could seem a little more logical.

 

[Screaming Metal]

What Mango said....!
After everything is said and done, 65 amps is alot. Most imports/ american cars that have cooling fans aren't that big unless they have electric windows and power seats. I know alot of 1Tons have the 100/120Amps since theres all the lights, the air, stereo, power seats and windows, plus they gotta throw alot of power to reconstitute that battery.... because of big current draws while cranking, along with heaters for glowplugs/gridheaters....
75/80 amps should give you everything you need and have a safety margine. After all, we're talking about charging the battery, lights, cooling fan, fuel pump, stereo (just to be safe), the draw from relays and gauges are almost nill....ign. sys as Mango point, Thats with electric water pump and trans cooler with fan. A healthy load, by T's standards, but not by cars with EFI's, etc...
EFI cars have intank pumps, fans on Rad's, Air, Stereos, GPS's, Lights, .....just something to think about....Another big draw item is the horn....and cooling fans are
How ofter are all these on at the same time? Unless you do alot of night driving....fuel pumps/ cooling fans are, or at least should be going on and off....

 

[Screaming Metal]

When you check your fuel pump and cooling fan, put a multi-tester inline with your load to measure your current draw....this will give you a accurate reading of what the charging system will see as far as load from these items....

 

[Swampdog]

Well I put the 140 Amp Alternator on and I have almost the same readings. I made an 8 guage wire from the Alt to the starter and it cut the voltage drop with the fan to almost nothing but the lights drop the voltage to 12.8 -13.0 range ( with the fan on and it it is on all the time in Louisiana in the summer). I got the 8 guage wire at work and got the terminals pressed on with a hyd terminal installation tool. I got to get the the terminal on the power wire from the battery to the starter terminal repaced. It is a little big for the terminal on the starter. Then I am going to just let it be.

Swampdog

 

[Hotrod46]

A couple of other points to throw in. High output alternators often won't put out anywhere near full load until they are well above idle. They may turn on and charge, but not at full capacity. The common SI GM series have this problem. The later CS series are supposed to be designed to put out at a lower RPM.

Most of the pulley sets that are sold for aftermarket applications (chrome and aluminum) don't have the ratio that stock pulleys do. The crankshaft pulleys I've seen run around 6" OD, while stock pulleys are 7-8". They slow the alternator down and can affect output.

They slow the water pump down. too. Less water being moved and if you have an engine driven fan, less airflow.

Mike

 

[PotvinGuy]

Well I put the 140 Amp Alternator on and I have almost the same readings. I made an 8 guage wire from the Alt to the starter and it cut the voltage drop with the fan to almost nothing but the lights drop the voltage to 12.8 -13.0 range ( with the fan on and it it is on all the time in Louisiana in the summer). I got the 8 guage wire at work and got the terminals pressed on with a hyd terminal installation tool. I got to get the the terminal on the power wire from the battery to the starter terminal repaced. It is a little big for the terminal on the starter. Then I am going to just let it be.

Swampdog

This gnaws at me. When you are moving, the alternator should have the system voltage up around 14. Where is your voltage gauge connected? Does the fuse panel get fed straight from the battery or from the starter terminal, and what size is this wire? Can you make a simple diagram of your power wiring? I suspect the path from the alternator to the gauge is causing the low readings.

But I don't think there is cause for alarm, unless your battery is running down.

 

[Screaming Metal]

This gnaws at me. When you are moving, the alternator should have the system voltage up around 14. Where is your voltage gauge connected? Does the fuse panel get fed straight from the battery or from the starter terminal, and what size is this wire? Can you make a simple diagram of your power wiring? I suspect the path from the alternator to the gauge is causing the low readings.

But I don't think there is cause for alarm, unless your battery is running down.

Yea, I usually doublecheck at the alt. output stud with my multitester....and check it agianst the gauge. I like to see what its putting into the system, not just output....

 

[Indycars]

ACDelco published a great amount of technical info on the website ACDelco TechConnect. Just click on the pulldown menu to select the alternator in question. You can see from the graphs that the CS-144 puts out significantly more around idle than the others.
http://www.acdelcotechconnect.com/html/tas_alt_main.jsp

I anticipated a possible cooling problem since I had very little clearance and had to run a Flexalite LowBoy fan rated at 2500 CFM. Therefore I used a CS-144 alternator and a 4 awg wire to maximize fan speed at idle, which is when the alternator is putting out the least current.
https://www.flex-a-lite.com/electri...versal/18-inch-loboy-electric-fan-puller.html

 

[Wild Mango]

This gnaws at me. When you are moving, the alternator should have the system voltage up around 14. Where is your voltage gauge connected? Does the fuse panel get fed straight from the battery or from the starter terminal, and what size is this wire? Can you make a simple diagram of your power wiring? I suspect the path from the alternator to the gauge is causing the low readings.

But I don't think there is cause for alarm, unless your battery is running down.

Good thinking by the Potvin Guy. What is happening is, the regulator in the alternator is a voltage sense device. It tends to track battery voltage in an effort to avoid over charge on the battery. When a load goes on the battery, the battery does work and the terminal voltage drops to reflect that. The regulator will bring the voltage up to carry the load but because the alternator and the battery are in parallel on the load, the voltage rise for the alternator will only reflect the volt drop caused by the load, not the open circuit voltage of a fully charged (or close) battery.

 

[PotvinGuy]

Here's the deal:

Your wiring may be slightly different, but the point is by the time the voltage gets from the alternator to the gauge, it goes thru lots of wire and the ignition switch, all of which have some resistance, and the loads at the end pull it down. The alternator is putting out 14 volts, but the gauge reads less. Common causes of really low readings are undersized wires (particularly the ignition switch wires), poor connections, or an iffy ignition switch. Try not to have any splices in the power wiring; butt connectors are asking for trouble.

If your battery is not running down, you're OK. If you'd like to see the voltage at the alternator or battery, hook a voltage gauge or multimeter right there and test with various loads on and at different RPM's.

Swampdog: is your alternator a 1-wire unit? They are popular, but I use one (GM CS100) with a separate sense lead that goes to the fuse panel; the alternator adjusts it's output so you always have full voltage at the panel.

 

[Hotrod46]

[I use one (GM CS100) with a separate sense lead that goes to the fuse panel; the alternator adjusts it's output so you always have full voltage at the panel.

[/QUOTE]

The Nippondenso alternator I used has a sense lead that I connected to a heavy duty junction block under the dash. All the loads come from that junction block. The sense function keeps the block at about 14.2 volts.

It's common on hot rods to see the sense wire on a GM alternator connected to the main battery stud on the back of the alternator. This will work, but will only maintain 14.2 volts at that stud. One wire alternators do this internally.

One wire alternators were originally made for stationary engines that run above idle most of the time. At least that was what I was told by a guy I know that rebuilds them. They require running up to high rpm to get them to excite. They will charge at low rpm's, but often not at full output.

Also, as Potvin stated, there can be considerable voltage drop in the dash wiring to the gauges. One wiring trick to help combat this is to run the hot wire to all the gauges in a loop. Most of the time the B+ power lead to the gauges will simply be daisy chained from gauge to gauge and can have pretty good voltage drop at the last gauge. By running an additional wire back to the gauge B+ source from the last gauge, you can reduce the drop at the last gauge, because there is no "last" gauge.

Mike

 

[Swampdog]

You guys are on to something. I replaced the power wire (one wire alt) from the alt to the starter with a #8 gauge wire with hyd crimped terminals of the proper size. I have 14.5/14.6 at the alt and the battery now. It only drops about .2 VDC with fan on and another .2 VDC or so with the lights on high. The volt meter reads 11.9 VDC with the fan and lights on at the same time. Anyway I got a new shinny alternator with a flat fan face plate.

Thanks

Swampdog