Longer alternator life when used to charge house batteries?

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johnny b

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Certainly NOT this unit....hi amp DC current would melt that thing.

Not a bad idea though.

Would need a temp sensor to trigger a slave relay that would in turn trigger a heavy duty disconnect relay.

OK as i was typing that.....a standard solenoid style house battery isolator has its trigger coming from an 'ignition on' source. A small disconnect relay inline on that wire triggered by a temp sensor would do the job.

Now then, I wonder what temp is considered TOO HOT for the alternator? Time to google!

:cool:
 

blars

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Switching off the load side of an alternator causes a voltage spike that can blow the diodes. What you want to do is reduce the field current instead. Better alternators will reduce their output when they get hot, rather than burn themselves out. This has been discussed on the boating LiFePO4 thread, since they can take maximum current until fully charged rather than cutting back like lead-acid.
 

SternWake

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A large depleted battery bank asking for a lot of current over wiring capable of passing it can certainly overheat an alternator, and even a single additional depleted battery bank adds tremendously to its work load, especially if it is a high$$ AGM battery.


Longer Alternator life can be obtained by keeping it cooler.

A cold air intake feeding the alternator ambient air instead of hot  underhood engine air can do a lot.  This has been on my to do list for years, but it is a want, not need type of thing and always has been put on back burner.

Reduction in the cabling diameter to the depleted house battery will also limit what the battery can ask for, and keep the alternator cooler.  The voltage drop on the thinner cable will lower the voltage delta between source and load, and voltage is electrical pressure so the effectively limits what the alternator has to make, but at the expense of faster recharging.

Reduction in field current would also reduce output and temperatures. But shutting off loads entirely on a spinning alternator can indeed cause Diode destroying voltage spikes, and these voltage spikes might also damage other electronics, such as the engine computer.

DO NOT remove a battery cable with engine running to test alternator on my modern vehicle.  This 'test' of an alternator could very well destroy it, and perhaps other things.  This is one of grandpa's holdovers that should be forgotten about.

Even if the engine battery is still on the system and one switches off the house battery bank which was asking for 50 amps, there could be a very short duration voltage spike that could damage electronices or the Diodes in the alternator and even if it does not instantly allow the magic blue smoke to escape, the damage is cumulative.

I am actually set up now to collect some data on alternator heating, but have not yet collected a lot of data.

What i have collected so far is a bit dismaying.

I drove around running errands, the engine was upto full temperature indicated by coolant and Oil pressure.  My battery was requiring about 24 amps to be held at 14.4 absorption voltage.

The final relay of the errand trip was about 1.5 miles of 25 to 40mph with headlamps on and blower motor on medium speed for an additional ~21 amp draw , then a 100 yard 10mph slow idle to my parking spot.

When parked and idling, lights and blower  now turned off, I checked the alternator temperature by turning on my digital multimeter and setting mode to fahrenheit, 119F.  As I continued to idle, with 24 amps into the battery, about 8 amps to run the engine, the alternator temp rose to 139.5f in a minute or two.  When I turned lights back onto high beams, and my 2 sets of fog lights, and my blower motor on high, this ~ an additional 60 amp load on the alternator, and at idle speed my alternator cannot keep up, the battery was now discharging to make up for what the alternator could not.  It was maxed out.  In 30 seconds of this alternator temperature had risen to 157 degrees.

So preliminary conclusions based on limited data, is that on my Dodge van, the airflow under the hood at speed makes a HUGE difference in alternator temperature compared to just Idling.  My engine also idles hot at 525 rpm according to my  aftermarket tachometer and cannot produce more than about 40 amps at that speed, but add a few hundred rpm and output easily climbs into the 60amp range.

So When i was driving with headlights on and blower motor on, It was around this 60 amp total level, and likely under 119f.

When parked idling and about half that total output, temperature increased 20F.
Maxing out the alternator at hot  idle, not moving, increased it another ~20F in less than 30 seconds.

So More data is really needed, and how applicable it will be to other alternators in other vehicles is an unknown variable, but it is safe to say that alternator temperature is directly related to both Load on the alternator,  and vehicle speed, as the alternator's fan pulling in 65F ambient air is much different than 120F ambient air.

One other data point I have is with a 2013 Ram powerwagon and a 160 amp alternator.  I depleted a new Lifeline GPL-31xt battery to 50%, and then hooked this depleted battery to a large winch connector that ran directly to alternator over ~12 feet one way of 2 awg cable.  When I flipped the switch to on, even the 5.7 liter Hemi engine note changed as the battery was demanding over 100 amps and the consuming ~ 4 engine horsepower to make that.

Alternator temperature quickly heated upto 220F, and then amps tapered to 86.  The battery voltage was still in the low 13's indicating the alternator was being limited in output, as more engine rpm did not increase the output.  It never rose above 86 amps again or 220 F searching for the hotspot with an IR temp gun, so I believe this alternator was temperature protected and 220F was where it said "Whoaaaa ho ho , Nellie, calm the Eff down"

I am not sure how these temperature protections are employed, or if this particular alternator is internally or externally regulated.

I have recently bypassed the voltage regulator in my engine computer, and have employed an adjustable voltage regulator instead.  Detail of this can be read here:
https://vanlivingforum.com/Thread-Your-Vehicles-voltage-regulator

With my dashboard mounted voltage potentiometer i can easily reduce alternator output by twisting the dial downward reducing the voltage delta.  If the VR is seeking to bring system voltage upto 13.4 volts, perhaps the alternator only needs to make 13 amps into the depleted battery, but if it was seeking 14.7v perhaps 45 amps additional amperage would be required to get the system voltage up that high with the depleted  battery gobbling up a huge percentage of total output.

I need to do more testing with a better temperature display I can safely see whilst driving, and do it with a depleted battery which can out a larger load on the alternator at any given rpm.

Another nice option of my adjustable voltage regulator is when i set it to the same absorption voltage as my solar controller, they work in conjunction to meet the electrical demand of accessories and depleted battery.  Before my VR mod, the ECM's VR would often choose 14.9v, and the second 14.5v was achieved the solar controller would go open circuit and not add anything, even if 12 amps were available and the battery would have appreciated it, and the alternator too would have enjoyed having to make 12 less amps.  If the battery is fully charged and can;t accept more than 0.4 amps current, then I can lower voltage and the Solar can actually meet the electrical demands of the engine ignition and fuel delivery is enough sun is available.

BTW my temperature sensor is my digital multimeter that uses a K type thermocouple.  It came with a 3 foot length one, but I have purchased additional 3 6 and 10 foot versions as they are rather inexpensive.  I used Arctic silver  5 minute thermal epoxy to hold sensor tip to the prepped alternator casing.  i will be doing the same for my battery and perhaps thermostat housing.

Here is a 4 input Ktype thermocouple for a reasonable price.

It should be interesting to see 4 different temperature displays at once:
 http://www.ebay.com/itm/4-Channel-K...527730?hash=item46374d5d32:g:QMoAAOSw7FRWVX7l



I'd love to see some data from another vehicle's alternator at various load levels and ambient temperatures, if anybody reading is as much of a nerd when it comes to this stuff.

I've always said Idling to recharge is a waste of cas in most circumstances, but my data has proven, at least on my vehicle that it significantly increases alternator temperature, as the alternator fan is not spinning fast enough, and the engine's fan is only spinning fast enough to keep the engine coolant at 195f.  This heat is effectively sent into the engine compartment surrounding the alternator.

So An Alternator that has a  the ability to produce half of its maximum rating at Idle speed, and is asked for everything it can make at idle speed by a depleted battery bank, could be a smoking hot alternator with a short lifespan.  So drive to recharge whenever possible, as Idling to recharge a depleted bank might seriously knock the alternator lifespan downward due to excessive heating.

Whether opening the hood will mitigate alternator temperatures at idle, would seem to be very vehicle specific as if the engine fan is able to direct a lot of airflow over the alternator with hood closed, it might run cooler than with hood open.

I am considering a ducted  3 inch bilge blower aimed at my alternator to bathe it in ambient air temp instead of underhood air temps.  Me thinks this would significantly extend alternator lifespan, and likely increase total alternator output, even accounting for the 3 to 5 amp load of the bilge blower.

If one is seeking an automatic way of prolonging alternator life, having a fan operated on a temperature acivated snap switch blowing ambient air at the alternator is likely the easiest way of reducing its temperature and prolonging its life.

Whether there is room for the fan and ducting is another matter.
 

SternWake

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2 alternators are better than one, no doubt. It can save one from being stranded if the Overheated alternator fails.

However the second alternator will still be susceptible to overheating if asked to charge depleted batteries at a high rate over thick cabling. Since it will not have to deal with vehicle loads such as the lights, blower motor, the load will be reduced to some degree, but perhaps the depleted batteries could ask for those extra amps anyway.

Since my AC compressor is now just a pulley, I have considered a second Alternator to replace it, but I have downsized my total battery capacity and do not really require a second alternator. Also I have a lifetime warranty on my alternator, i replaced it last fall for free in 15 minutes after 9 years of hard service where it was maxed out often.

But if my alternator required a lot of labor to replace and 250+$ no doubt I would seek to lessen its work load however I could. I'm not going to destroy a 650$ alternator to prolong the life of a 150$ battery, but a remanufactured lifetime warranty free unit, as long as I am near an oreilly's, well i'll work the SOB as hard as i want to get extra battery life.

Also having solar, and knowing my engine requires 8 amps to run, I could drive a considerable distance without a functioning alternator. if i drive at noon in summer 5 amps might make it into the batteries with a failed alternator.

I have not tested the engines electrical demands at higher than Idle speeds though. the fuel pump is always 4.2 amps but the injectors and ignition would likely increase their consumption at higher rpms, how much, I did not test.
 

johnny b

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Another reason I love this forum....continuing education.
(I let my 'quick fix' mentality get ahead of my 'think it all the way through')....gotta remember the ol logic equations......'if this, then that' !!   :blush:
 

MikeRuth

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Adding a second alternator requires some engineering and you need the room to do it as well. On my 2007 ford e-150 there is absolutely no room.
Another issue is my alternator is mounted on top of the engine. Could it get any hotter? I'm seriously thinking on a system to blow air on to the alternator but to be most effective I believe a fan will be needed. I say that because I too have seen alternator performance change with temp. It's not as bad in winter temps but in the summer with the AC on at idle I will not get more than 13.8 when normal is 14.4.
When stationary the fan would blow that cooling air. While moving I have not seen the drop in voltage or significantly less drop ie 14.0 ish

Just for reference at 80f outside my 130 amp alt, can produce about 90 amps hot sustained. At least that's what I last saw when testing with a roughly 100 amp load on my inverter and the engine rpm's at 1250, that's with the house and starter connected to the alt at the same time.
I had 90 going to the house and 25 to the starting battery.
 

SternWake

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Dodge, in their ultimate wisdom decided to install the alternator so that its backside, where the rectifier bridge is located, is about 1 1/8" away from the exhaust manifold.

Mine has this little heat riser collector/shield over the E manifold for feeding the engine warmer air when warming up, and I extended this device to act as a heat shield for the alternator, and at hot idle from then on, I was getting 5 more amps. This was more effective at idle speed than was a smaller alternator pulley in increasing output.

My alternator pulls in air from the back and it exits out the front by the pulley, So in theory I could make a shroud on the backside of the alternator with a feed tube and the alternator fan could pull in ambient air instead of underhood air and no external fan needed.

But in reality making a tight fitting shroud around the wires, in the space available, would likely turn into a cursing fit and the nearest tool could be launched into low earth orbit followed with a stream of sky blackening curses.

While heat certainly impacts what the ideal voltage allowed is, and a hot alternator is less capable of producing anything near its rated output, the voltage regulator itself might be able to sense underhood temperatures and or battery temperatures and limit maximum voltage, and thus alternator output, so it could be that the alternator is not max out or overheating, just that a voltage regulator might have temperature compensation somehow and reduces max allowable voltage.

Remember that vehicle's electrical systems are designed to keep a fully charged engine battery fully charged, or at least above 80% while powering all vehicle loads. They were never wired nor intended to charge depleted house batteries which are a huge additional load, especially when the hose between City water and flowerbed is as thick as a firehose, such as when a dweller adds a thick copper circuit between alternator and house bank.

In Mainesail's writeup on Lifepo4 batteries, he touches on alternator recharging of them. Since they are of even lower resistance than high$$ AGM they truly can max out and fry an alternator quickly, as they will take everything until 95% charged, where as lead acid is about 80%.
There is also good reading in the following link which might help put some pieces together for others regarding lead acid battery charging.

225F seems to be the upper allowable limit on alternator temperature. The boaters have specialized voltage regulators which will limit field current, and thus output, to save the alternator and the belt driving it. These are in the neighborhood of 750$

http://www.pbase.com/mainecruising/lifepo4_on_boats

So one can see that alternator recharging can be taken to extremes to both maximize output, but also to keep the alternator from smoking itself trying to feed a hungry bank of batteries.
 

Konaexpress

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Here's a stupid thought, how about a small vertical windmill that helps charge while driving? They do this on boats.

Just a wild stray thought fluttering about......

John

EDIT: Now that I think a bit more, a horizontal one would do just fine. A long squirrel cage hooked up to an electric motor maybe. You can find them on air conditioners and swamp coolers. Wonder what it would sound like going down the road? :D
 

SternWake

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It would create more drag on the engine than a belt driven alternator.

Keeping an alternator cooler is the best way to extend its longevity. This can be done by reducing its load, or increasing its inherent ventilation/ heat dissipation abilities.

Idling parked to recharge a well depleted house or engine battery 'might' be the time the alternator gets hottest. This is very vehicle platform dependent and depends on its underhood airflow, the actual ability of the alternator at idle speed, and its own fans ability to move air through it.

I need to do more testing since I can now test alternator temperature, but the preliminary test had my alternator temp skyrocket when parked and idling and maxed out, compared to a similar output when driving. Even not maxed out at ~32 amps output at parked idle, it was significantly hotter than when driving with ~ 55 amps of load on it.
 

Konaexpress

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You think so even if you made an air dam around it with a small opening that opens on to the paddles/blades going with the wind? Blocking the air from the paddle as it comes up and around or vise verse? hmm would love to try this........

Back on topic......

John
 

SternWake

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If you were to put a 100 amp alternator on a 10 speed bicycle tire in a proper ratio, get upto a comfortable speed, and only then feed the alternator or 8 amps of field current, you might break a leg.

It takes about 1 engine HP for the alternator make 25 amps output.

A wind generator is a horse of a different color, and will never approach the abilities of an engine driven alternator, until the size formats are the frontal area of an 18 wheeler.
 

highdesertranger

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as for the windmill on your van, you will create more drag than the energy produced. first rule of physics. energy is not free. you never get more energy then the amount of energy you put in. in other words if you could, you would have a perpetual motion machine. highdesertranger
 

Konaexpress

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SternWake said:
If you were to put a 100 amp alternator on a 10 speed bicycle tire in a proper ratio,  get upto a comfortable speed, and only then feed the alternator  or 8 amps of field current, you might break a leg.

It takes about 1 engine HP for the alternator make 25 amps output.

A wind generator is a horse of a different color, and will never approach the abilities of an engine driven alternator, until the size formats are the frontal area of an 18 wheeler.

Sorry, a misunderstanding here. I didn't intend for it to compete with the power f an alternator. I meant to use it for a top off or trickle charge.

Sorry,
John
 
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