Voltage drop with fan on

[sifan]

The car is a 1995 Toyota Tercel (MT, no AC, no PS) with 287K miles on the original engine. I hook up a Scangauge to the OBDII port, so, I can observe the voltage/RPM/MPG/coolant temp while driving. After installing a brand new Odyssey battery PC1200 (a dry cell battery) two days ago I pay speciall attention to the voltage reading since it requires constant voltage to recharge. The voltage remains constant most of the time around 14.1V and occassionally jumps to (no more than) 14.2V during daytime driving.

While driving home from work tonight with headlights (low beam) and fan (at medium speed) on I noticed the voltage dropped from 14.1V to 13.6V when I stopped at a traffic light with the engine idling. To find out the culprit I turned off the headlights and fan respectively. To my surprise it was the fan that drained the voltage which was not even set at the max speed. Once the fan was off the voltage returned to 14.1V at idle with the headlights on. As car was moving the voltage remained at 14.1V even with the fan being turned on.

What could cause the fan to reduce voltage? What can be done to fix this problem? The weather is like winter here now, and I need the fan to circulate heat but without ruining a $240 battery.

 

[brianl703]

Try using a multimeter to check the voltage directly at the battery. See if it really is 13.6V at the battery with the fan on medium and the engine idling.

 

[sifan]

I will test it tomorrow since it is really late now.

What would be your opinion if the battery is or isn't at 13.6V under such a condition? I am not familiar with electricity and am wondering the purpose of this test. Thanks.

 

[chevrofreak]

Fans use a lot of power, even when run at less than full speed. I have a Kill-A-Watt power meter to measure the power usage of 110v devices, and the difference between high and low on some of the fans I have tested wasn't all that large. One of them measured 25 watts on low and 35 on high, and high was significantly faster than low.

 

[eljefino]

You're fine, stop worrying. May try goosing the gas to a high idle to see if you get back to 14.1.

Alts only make ~30 amps at idle, and I'm sure the tercel has one of the smallest lightest weight alts you could find.

Lots of cars run off the battery at idle with enough stuff on, but it doesn't hurt anything because of the bursts of higher speed successfully fixing things.

Also possible your whole interior feed is off one maxifuse and a 10 gauge wire so you have a voltage drop inside when the fan is running.

 

[brianl703]

Originally Posted By: sifan

What would be your opinion if the battery is or isn't at 13.6V under such a condition? I am not familiar with electricity and am wondering the purpose of this test. Thanks.


The purpose of testing directly at the battery is to rule out a voltage drop between the battery and interior fusebox, where your scangauge and the fan are most likely both powered from. Also to rule out a voltage drop in the grounds for both of those.

 

[brianl703]

I looked it up..the 1995 Tercel with the manual trans came with a 60 amp alternator.

The idle output of that alternator is likely to only be around 30 amps or so. Your fan probably takes at least 15 amps, and that leaves 15 amps to charge the battery and run the rest of the car.

The only solution you have is to put a larger alternator in or get a less fussy battery.

13.6V won't harm a regular battery. I've no idea what makes the Odyssey battery so fussy that 13.6V isn't enough for it.

 

[brianl703]

Originally Posted By: eljefino

Alts only make ~30 amps at idle


Most of the more recent ones make a lot more than that at idle. Ford's 3G alternator, which I do believe came out in 1991 or so, is designed for high output. The 130-amp version outputs 80 amps at idle; the 90-amp version used in the 91-newer Escort is around 50 amps at idle. The 120-amp alternator in my 2006 Saab 93 is capable of around 100 amps at idle, according to my testing with a clamp-on ammeter.

The usage of electric cooling fans has driven the need for alternators with good output at idle. After all...those fans use a lot of power and they're most likely to come at idle.

(It probably also reduces in-warranty battery replacements).

 

[Steve S]

Fans draw lots of power look at the fuses rating in the circuit.

 

[PandaBear]

0.5V when there is a large current draw makes sense.

 

[IndyIan]

I have a scanguage too, and I can see why manufacturers don't put in digital gauges! Too much information sometimes.

Anyways, I just replaced the resistor block for the interior fan on my Neon. Lowest speed has the biggest resistor and full speed has no resistor and the middle speeds have a couple resistors inbetween. So no matter what fan speed you use, it draws the same current. Also the resistor block is probably in the interior fan intake so it gets some air flow, so in the summer don't use the lower speeds as you are heating the air blowing in...
The fan must draw alot as the resistor block plug had melted leaving me only full speed. I just cut the plug off and soldered the wires to the new block.
Ian

 

[sifan]

I checked the voltage at the battery with engine idling, headlights on, and fan at full speed. The voltage matched the reading provided by the ScanGauge at 13.5V.

The below link shows the charging information on Odyssey batteries:

http://www.odysseybatteries.com/charging.htm

The spec is for battery charger that requires voltage between 14.2V and 15V. I wonder if my car alternator is so underpower that might damage the battery. I will need to talk to the technical support to find out more info.

 

[sifan]

Just called the Odyssey tech support. The most knowledgeable guy is out on vacation, and won't return till next Monday.

I did some search on the internet for a high output alternator for my car. The OEM replacement ones are all rated at 60a for manual transmission. It seems there are no high performance alternators on the market specially designed for '95 Tercel. I found an universal one rated at 100A, but am not sure if it will fit.

what are the drawbacks for installing a higher output alternator? Will it need the engine to work harder? Is it good for the engine? Will the engine tune-up spec be changed from the factory one?

 

[mechtech2]

chevrofreak has the right idea.
Fans take power. Even at low settings, there is a resistor that will suck up power.
As a side note, remember that alternators charge a bit more at low temps, and less at high temps. The regulator adjusts for temps either by design or a good happenstance.

 

[Mau]

its a bloody tercel! I'd be surprised if the odyssey tech says it requires between 14.2 and 15v all the time, if he/she does say that then I'd just return or sell the battery and pick up a regular battery (I recommend Interstate brand).

 

[PandaBear]

Originally Posted By: sifan

what are the drawbacks for installing a higher output alternator? Will it need the engine to work harder? Is it good for the engine? Will the engine tune-up spec be changed from the factory one?


Most likely fit and finish issue and whether it will overcharge the battery and blow it up (have seen it before).

 

[IndyIan]

I also just put in a new battery into my Neon. On the old battery voltage would bounce around from 14.2 to 14.6 driving down the highway at 2400 rpm. With the new battery the voltage sits at 14.1 and rarely changes... Why its lower I don't know but the car cranks over much faster, etc.
I wouldn't worry about the battery or the existing alternator to much. Your new battery will hold onto a charge much better so the alternator has to do less than when you had the old battery in there.
Ian

 

[JHZR2]

On my BMW, with a new hella 14.1V regulator, Ill see drops like that quite easily with loads like AC/fan and headlights. Nothing odd there.

I also see change in voltage with (I guess) alternator temperature and battery SOC. Typically Ill be down to about 13.3-13.5V depending upon temperature, at steady state with the AC, fan, stereo and lights on.

 

[brianl703]

Originally Posted By: sifan

what are the drawbacks for installing a higher output alternator?


One major drawback is, if it's the factory sized alternator rewound for higher amperage, it will probably have lower output at idle--which means it won't solve the problem.

I put a rewound alternator in my Mustang. The factory alternator was 75 amps, the rewound was 130 amps. Same physical size alternator. The output of the rewound 130 amp alternator at idle was worse than the factory alternator.

I ended up putting a 130 amp 3G alternator from a Taurus in there. It's physically larger and required grinding part of the mounting bracket away, but other than that it was a direct bolt-in. It was almost a direct plug-in except Ford changed to a bolt stud for the output as opposed to a spade connector. So I cut the old connector off and crimped a ring terminal on.

Plenty of voltage at idle now and I think it's easier on the battery now.

 

[OVERKILL]

Originally Posted By: brianl703
Originally Posted By: sifan

what are the drawbacks for installing a higher output alternator?


One major drawback is, if it's the factory sized alternator rewound for higher amperage, it will probably have lower output at idle--which means it won't solve the problem.

I put a rewound alternator in my Mustang. The factory alternator was 75 amps, the rewound was 130 amps. Same physical size alternator. The output of the rewound 130 amp alternator at idle was worse than the factory alternator.

I ended up putting a 130 amp 3G alternator from a Taurus in there. It's physically larger and required grinding part of the mounting bracket away, but other than that it was a direct bolt-in. It was almost a direct plug-in except Ford changed to a bolt stud for the output as opposed to a spade connector. So I cut the old connector off and crimped a ring terminal on.

Plenty of voltage at idle now and I think it's easier on the battery now.


The 2G alternators were simply junk. The 3G's are a far more efficient design period. I also have the 3G swap on both my vehicles; 130A units, one from a Taurus, other from an SN95.