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Old 10-23-2017, 03:34 PM   #1
weq92f
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too many amps, need better alt?

Going to add electric fans which when running will draw 24 amps ( 2x12 ). Calculating my total amp draw across the entire system I find that if everything is actuating all at once my total draw would be 121 amps.

My alt is currently a CS-130 at 105AMP. So, it's pretty close at the moment to being about the right size for my system without the fans ( amp draw without fans is currently 97 if all electrics came on at once! ).

What'dya think, should I upgrade the alternator as well when I add the fans?

Here's the amp calculations just for grins:


dizzy 8
Electric cooling Fans 24 total ( 12x2 )
Headlights 15
tail led lights 2
gauges 5
Radio/Stereo 8
Atomic EFI unit w/pump 30 max: normal: 14-18 -- I calc'ed 18
MSD 6a box 6 max
electric windows 10?
electric door locks 4
electirc seats 10?
A/C blower fan 7 on high
A/C clutch 4

121 total if all is running at same time
97 without the fans added

Thanks,

-klb
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Old 10-23-2017, 09:04 PM   #2
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Re: too many amps, need better alt?

I think your numbers are high in lots of places. If you are running a msd box the distributor is pretty much not going to draw much, dont think you need to have the door locks on the list. They only pull for a split second. What are the chances of all this on and at full load all at once? I think you will be fine with what you have.
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Old 10-24-2017, 12:29 AM   #3
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Re: too many amps, need better alt?

I agree, you can always upgrade the alternator if it doesn't meet your needs. Remember when they went to the CS alternators they were used on cars and trucks with fans and power windows, Locks etc.
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Old 10-24-2017, 12:39 AM   #4
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Re: too many amps, need better alt?

I agree with PG.

I would add up all your heavy hitters that could be on at once and at idle.
Like fans, fuel pump, AC, headlights and stereo.
I would dig out the DMM and measure voltage at the battery and alt to figure out what alt you need. Most alternators amp rating are at the max rating and not at engine idle speeds. So a 105 amp alt may only put out 65 amps at idle (800 RPM), and 105 amps at like 1200 RPM. Just something to add to the equation.
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Old 10-24-2017, 08:24 AM   #5
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Re: too many amps, need better alt?

Thanks guys! The consensus seems to be my alt ( 60-80A idle, 105A max ) will probably do the job just fine. If not, a couple hundred bucks will get me an easy swap to the next level at 140A or so down the road.

So at idle with fans spinning and the usual stuff on, my gauge should still read around 13 Volts at the dash? If I see it dip to 12 or below, that's no good right?

Thanks,

-klb
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Old 10-24-2017, 02:29 PM   #6
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Re: too many amps, need better alt?

Quote:
Originally Posted by weq92f View Post
Thanks guys! The consensus seems to be my alt ( 60-80A idle, 105A max ) will probably do the job just fine. If not, a couple hundred bucks will get me an easy swap to the next level at 140A or so down the road.

So at idle with fans spinning and the usual stuff on, my gauge should still read around 13 Volts at the dash? If I see it dip to 12 or below, that's no good right?

Thanks,

-klb
Correct. You should actually see around 14.3 volts running at idle. Use a digital multi-meter. Also a good indicator is if your headlights go dim at idle and get brighter when you rev it when all accessories are on.
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Old 10-27-2017, 10:11 AM   #7
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Re: too many amps, need better alt?

My formula:

Alternator should be running @ 75% capacity no more.

Total amp draw should be 75% of alt max amp rating. This ensures a good long alternator life.
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Old 10-27-2017, 03:06 PM   #8
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Re: too many amps, need better alt?

One thing I didn't see in your calcs are the wipers.

Very likely you could be running headlights, running lights, wipers, blower motor on max and AC + stuff needed to run the truck all at the same time. Quick test would be to turn all that stuff on at a bit above idle and watch the volts. If they stay up, you are good.

Don't worry about things like locks, windows and adjustable seats since the battery can easily supply them for the seconds they are on.
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Old 04-09-2019, 07:40 PM   #9
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Re: too many amps, need better alt?

Today I'm doing some testing in 85* outdoor temps. With everything on ( cooling fans on high, AC blowing on high, lights, radio wipers,...), I'm reading 12.5 volts at the battery, 13.5 volts at the alternator post and the gauge is reading around 12, likely closer to the battery reading but lower. This is at idle in neutral ( auto trans ) at about 675 RPM. In gear, the RPM doesn't drop very much.

Minus the lights and wipers, this is pretty much the norm for summertime driving in terms of the state of the charging system during stop and go summertime driving. At speed, the fans will kick off.

What do you guys think, is my alt keeping up well enough here at full load? BTW, most of the big draw items are wired directly to the alt post.

-klb
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Old 04-10-2019, 05:31 PM   #10
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Re: too many amps, need better alt?

Checked all the connections today and did some further measuring of things after a longer drive. Today I measured 12.4 volts at the battery, 13.3 at the alt post and the gauge was reading around 12. This while all the eletrics were on full blast.

Actually had to sit idle at a train for a good 10 minutes ( near constant cooling fan on high and A/C blowing - I think the fans cycled off once or twice ) before pulling up into the drive and measuring with the DMM. After killing the engine the battery measured 12.47 volts.

-klb
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07 335 sport turbo 6sp
94 Trans Am GT LT1 6sp posi -- sold after 22yrs
99 540 sport V8 6sp -- sold
73 240z L24 4sp -- given to friend
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Old 04-10-2019, 07:36 PM   #11
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Re: too many amps, need better alt?

I would be a bit concerned about the 1.0 volt drop alt to battery. Maybe start by putting a larger gauge wire from the alternator to the battery.

Where is the volt meter connected? Under the dash?
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Old 04-10-2019, 11:05 PM   #12
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Re: too many amps, need better alt?

Battery should be seeing what the alt is seeing for voltage. I’d like to see a diagram of how your power distribution is set up. Sounds like the remote voltage sensing is not liking however you have everything wired.
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Old 04-11-2019, 11:48 AM   #13
weq92f
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Re: too many amps, need better alt?

Quote:
Originally Posted by 67 Burb View Post
I would be a bit concerned about the 1.0 volt drop alt to battery. Maybe start by putting a larger gauge wire from the alternator to the battery.

Where is the volt meter connected? Under the dash?
Will have to chase it down to determine...

Quote:
Originally Posted by gmachinz View Post
Battery should be seeing what the alt is seeing for voltage. Id like to see a diagram of how your power distribution is set up. Sounds like the remote voltage sensing is not liking however you have everything wired.
A PO installed a new harness, Painless I believe. It's going to be an adventure tracing down the leads to figure out exactly how it's all wired up. The gauge of the leads connected to the alt all appear to be on the small end of the scale and none of them make a direct path to the battery. Appears to me any path to the battery goes through the fuse box, probably through the volt gauge and through some other wiring that is definitely not of the proper gauge.

The cooling fans pull directly from the battery. If the alt doesn't really have a direct circuit to the battery, could the amp draw of the fans on the battery cause damage to the wiring ( possible fire ) between the alt and the battery due to the draw?

As you may have figured, I'm not a great electrical guru!

-klb
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Old 04-11-2019, 12:09 PM   #14
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Re: too many amps, need better alt?

Well the problem I have with Painless and even AAW to a degree is that they follow pretty damn close how GM originally designed the circuits...complete with shortcuts, barely adequate wiring sizes and type, etc. There should be more of a focus on modernizing the electrical circuits but thats more difficult to do that to just copy GM 100%.

The various power leads do need fused protection BUT-there should not be any accesssories pulling directly from the battery-instead all power runs should come from a single common +12 junction-and from that junction the alternator remote voltage sensing wire also needs to land there. The reason is because its easier for the voltage regulator to adjust to changing voltages if it is directly upstream from all sources of power-everything passes thru sort of like a floodgate and the regulator will try to maintain system voltage of 14V or so.

Now, if you are running multiple things and pulling power from different places, the alternators’ regulator can’t “see” the changes in voltage demands as easy so it has a hard time keeing up....thats why there is imo a significant amount of voltage drop (over 1V) in your system. Moreover you have:

Too many power runs
Not large enough wire diameter
Too long of wire lengths
Not updated enough to run modern accessories

This isnt to say what you have now wont work or continue to, I’m just saying its not optimal-alternators don’t like being overworked...and not running a sustained higher voltage (over 14V) makes it tuff on any alternator to live a long life. And consequently, your accessories wont live as long either. 12VDC things like actuators, motors, etc are designed to run at 16V, so the closer you can get to that the less amperage they require to do the work. So if that alternator is hovering around a system voltage of 12-12.5 all of your devices are pulling more amperage than they would use at 14V. That is why bigger is always better with regards to wire sizing and the charging system-but it needs to be thought out.
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Last edited by gmachinz; 04-11-2019 at 12:14 PM.
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Old 04-11-2019, 01:03 PM   #15
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Re: too many amps, need better alt?

.
Thank you for this explanation, really helps me understand what may be happening.

Before adding the fans, the system was OK. Adding the fans and particularly my decision to wire the relays to the battery ( through a breaker ) has pushed it a bit too far.

There are other accessories that are direct draw from the battery as well for example the headlight relays are wired there.

All of these power leads should be combined onto a common distribution block along with those that are wired directly to the alt post and then a larger gauge lead should be run from the alt post to the block? Then the block would be connected to the battery by an equally large gauge cable...say...6?

-klb
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Old 04-11-2019, 02:43 PM   #16
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Re: too many amps, need better alt?

Yes-I think that will eliminate most of your voltage loss. Let us know before/after results too! So take a reading at the alt post before and after as well as at your interior fuse panel batt cavities before/after.
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Old 04-13-2019, 01:01 PM   #17
weq92f
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Re: too many amps, need better alt?

.
After further review...

I think I'm understanding this a bit better now. First, I don't have a CS-130. That was a miss on my part. It's a CS-130 looking case but it's a single wire alt made by tuff stuff.

There are 3 leads attached to the single pole. One to the starter solenoid, one to the main fuse panel power and the other powers the relay bank for headlights/horns.

The cooling fans, starter and a few other leads are connected directly to the battery.

Given this, I think what I need to do is go back to a 3 wire internally regulated alternator so that I can use the remote sense wire to keep 14 volts at a common power distribution block where everything gets power.

That is, unless there is a way to wire the one-wire alt to emulate the same setup?

-klb
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