ammeter to voltmeter
Pro
Joined: Dec 2006
Posts: 582
Likes: 3
From: Glen Allen (Richmond) Virginia
I couldn't at first imagine why the Spal engineers would say this.
After some thought, I think I may have a possible answer. It involves the resistance wire that runs from the alternator to the battery lug on the starter (it's the wire that routes alternator charge current to the battery and battery current to the loads when alternator output is insufficient).
Lets assume you've got all electrical loads on; headlights on bright, AC fans on, stereo on, etc. and you turn the engine off. Now all current required comes from the battery and flows through the resistance wire (fusible link). Now a large current is flowing through the wire. The factory sized the wire to withstand this current. I think someone said it was rated at 30 amps. Now, if you have the Spals connected to the alternator, the Spal current will also come from the battery through this wire. Say the Spal takes 20 amps. Now you've got a current that could exceed the current max for the resistance wire (fusible link). This could cause the wire to fail. For example, your car loads might be 20 amps and 20 extra amps for the SPAL (connected to the alternator) would result in 40 amps, exceeding the 30 amp rating of the resistance wire.
Anyhow, my 68 doesn't have AC, etc, so I think I still keep by fans on the alternator. I like the idea that the ammeter reads 0 when the fans are on.
After some thought, I think I may have a possible answer. It involves the resistance wire that runs from the alternator to the battery lug on the starter (it's the wire that routes alternator charge current to the battery and battery current to the loads when alternator output is insufficient).
Lets assume you've got all electrical loads on; headlights on bright, AC fans on, stereo on, etc. and you turn the engine off. Now all current required comes from the battery and flows through the resistance wire (fusible link). Now a large current is flowing through the wire. The factory sized the wire to withstand this current. I think someone said it was rated at 30 amps. Now, if you have the Spals connected to the alternator, the Spal current will also come from the battery through this wire. Say the Spal takes 20 amps. Now you've got a current that could exceed the current max for the resistance wire (fusible link). This could cause the wire to fail. For example, your car loads might be 20 amps and 20 extra amps for the SPAL (connected to the alternator) would result in 40 amps, exceeding the 30 amp rating of the resistance wire.
Anyhow, my 68 doesn't have AC, etc, so I think I still keep by fans on the alternator. I like the idea that the ammeter reads 0 when the fans are on.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
I dunno if the pissing contest between me and Brain Baskin of DCC fame got deleted or not, I frankly don't care but it's allmost a year old now....his controller and MAYBE the Spal controller that Tom DeWitt has had so much trouble with he stopped selling it for a while, do not like input from alternators directly....apparently...due IMO to faulty design...
if you examine the wiring diagrams, you find so many incorrect statements above, I simply don't have time to follow up on each one...
and additionally the topic is a burn out for me....as I have over some 40 years of hotrodding, been through these many GM and other electrical systems I know what seems to be every damn wire by heart...
no freeking WONDER I can't sleep....
at any rate, IF you use a simple single relay setup for both fans and run off the alt direct ....you will NOT have any problems....
IF you run a dual relay set for two differant temps one each fan...you will not have any problem either....and IMO THAT IS THE WAY TO DO IT.....
and it's all run off the alt wire...the + side of the relay coil is set to an IGNITION source, on only when engine is theoretically running...not some damn accessory wire...so the relays can't close if you are stopped with engine still, and just listening....
these PWM controllers are not adequately designed, and hooking off the battery as they desire is cause they too cheep to do it right, and I know what I talking about....
CASE CLOSED......
my last and only post in this thread....
Race Director
Joined: Jun 2000
Posts: 10,036
Likes: 668
From: FL
I couldn't at first imagine why the Spal engineers would say this.
After some thought, I think I may have a possible answer. It involves the resistance wire that runs from the alternator to the battery lug on the starter (it's the wire that routes alternator charge current to the battery and battery current to the loads when alternator output is insufficient).
Lets assume you've got all electrical loads on; headlights on bright, AC fans on, stereo on, etc. and you turn the engine off. Now all current required comes from the battery and flows through the resistance wire (fusible link). Now a large current is flowing through the wire. The factory sized the wire to withstand this current. I think someone said it was rated at 30 amps. Now, if you have the Spals connected to the alternator, the Spal current will also come from the battery through this wire. Say the Spal takes 20 amps. Now you've got a current that could exceed the current max for the resistance wire (fusible link). This could cause the wire to fail. For example, your car loads might be 20 amps and 20 extra amps for the SPAL (connected to the alternator) would result in 40 amps, exceeding the 30 amp rating of the resistance wire.
Anyhow, my 68 doesn't have AC, etc, so I think I still keep by fans on the alternator. I like the idea that the ammeter reads 0 when the fans are on.
After some thought, I think I may have a possible answer. It involves the resistance wire that runs from the alternator to the battery lug on the starter (it's the wire that routes alternator charge current to the battery and battery current to the loads when alternator output is insufficient).
Lets assume you've got all electrical loads on; headlights on bright, AC fans on, stereo on, etc. and you turn the engine off. Now all current required comes from the battery and flows through the resistance wire (fusible link). Now a large current is flowing through the wire. The factory sized the wire to withstand this current. I think someone said it was rated at 30 amps. Now, if you have the Spals connected to the alternator, the Spal current will also come from the battery through this wire. Say the Spal takes 20 amps. Now you've got a current that could exceed the current max for the resistance wire (fusible link). This could cause the wire to fail. For example, your car loads might be 20 amps and 20 extra amps for the SPAL (connected to the alternator) would result in 40 amps, exceeding the 30 amp rating of the resistance wire.
Anyhow, my 68 doesn't have AC, etc, so I think I still keep by fans on the alternator. I like the idea that the ammeter reads 0 when the fans are on.
Spal instructions here: http://www.s10v8.com/store/FRH-185FH-195FH.pdf
I actually like having the Spals hooked to my battery (starter) and having the ammeter move when the fans kick in. For me, it is a good check that they come on when the temp gets up to 195 and shut off when it cools to 185.
Pro
Joined: Dec 2006
Posts: 582
Likes: 3
From: Glen Allen (Richmond) Virginia
Man....everybody is touchy about this one I guess the best answer is "it's your car put it where you like it" Seriously, this one bugged me so bad that I called the spal guys back and guess what? I got a different answer they said no problem with the alternator in most cases. If you think about it they write the instructions for all cars (not a separate set for rear batteried Corvettes) and the battery is up front so maybe they saw that as a close place to hook up.
I may try the alternator setup only because I get tired of people saying that my car is overcharging when the see the amp gauge at 25-30 amps.
I could always put a couple of small LED lights up in the AC vent so that I can see when the fans are powered up
Seriously, this one bugged me so bad that I called the spal guys back and guess what? I got a different answer they said no problem with the alternator in most cases. If you think about it they write the instructions for all cars (not a separate set for rear batteried Corvettes) and the battery is up front so maybe they saw that as a close place to hook up.I may try the alternator setup only because I get tired of people saying that my car is overcharging when the see the amp gauge at 25-30 amps.
I could always put a couple of small LED lights up in the AC vent so that I can see when the fans are powered up
Advanced
Joined: Aug 2005
Posts: 75
Likes: 0
From: Denver Colorado
I don't understand why you would connect your fans directly to the battery (or big lug on the starter - same thing). All of the electrical loads in the car are powered from the alternator, most notably large loads such as AC fans and headlights. I think M.A.D Electrical has a good article about this (don't know if MAD still has his webpage - he was having health problems). Why not power the fans from the alternator just like everything else?
The battery is connected to the alternator by a wire with some resistance, it's a fusible wire. Current going to, or from the battery, creates a small voltage across this wire. This small voltage is "read" by the ammeter. The sense is that a small positive voltage causes the ammeter to read + amps and small negative voltage results in - amps. Although the ammeter is calibrated in "amps" its really a voltmeter reading the volts across the resistance wire (fusible link).
If you power your fans from the battery lug, the current they draw is coming from the alternator (otherwise the battery would go dead pretty soon). This causes the ammeter to read a "charge" current, when the battery is in fact not charging. The ammeter is now reading the current going to the fans. This is OK, but I thinking you're stressing the resistance wire (fusible link). You don't want this to ultimately blow open.
When my fans run, the ammeter reads 0. Also, I don't need a ammeter to tell me my fans are on. I can hear them, even over the sound of the factory sidepipes.
The battery is connected to the alternator by a wire with some resistance, it's a fusible wire. Current going to, or from the battery, creates a small voltage across this wire. This small voltage is "read" by the ammeter. The sense is that a small positive voltage causes the ammeter to read + amps and small negative voltage results in - amps. Although the ammeter is calibrated in "amps" its really a voltmeter reading the volts across the resistance wire (fusible link).
If you power your fans from the battery lug, the current they draw is coming from the alternator (otherwise the battery would go dead pretty soon). This causes the ammeter to read a "charge" current, when the battery is in fact not charging. The ammeter is now reading the current going to the fans. This is OK, but I thinking you're stressing the resistance wire (fusible link). You don't want this to ultimately blow open.
When my fans run, the ammeter reads 0. Also, I don't need a ammeter to tell me my fans are on. I can hear them, even over the sound of the factory sidepipes.
