How to burn out your alternator while direct charging LiFePo4

[B and C]

Not one alternator had the fan on the drive pulley unless this is the way they make them now (no fan). This is the reason you should never idle to charge either, no airflow.

[sternwake]

The fans on most of the better alternators today are internal to the casing.

Note, the amps they were producing, 96 on the one test, is well within what my single group 27 northstar AGM was able to consume when newer and healthy.

They also did not factor into the equation that the large drive pulley of an engine spins the small alternator pulley 5 to 7 times faster than engine rpm. They were using an electric motor whose pulley was nearly the same as the alternator pulley, for nearly a 1 to 1 ratio .

But their points and conclusions are very valid, low rpm the alternator might be able to make a lot of amps still, but it cannot dissipate the heat it generates and can burn itself out if it has no current limiting function/ ability.

While my single group 27 northstar, when it was new and well depleted, could suck up perhaps 96 amps for 10 minutes before that number would start tapering, a larger bank of AGMs and of course Lithiums, could suck up that much amperage, and much more, for much longer, creating much more opportunity to overheat and fry the alternator.

So many people think a huge alternator rating means it can always output that much current at almost any rpm, but in reality that is the absolute maximum it can produce spinning fast, when still cold, with huge loads capable of sucking up everything it can make.

Idling to recharge is unwise. More engine rpm not only makes more amperage, but keeps the alternator much cooler, not only as the alternators fan is cooler but the vehicle movement means the alternator is not ingesting 200F + air, but much cooler air instead. is a high idle enough to keep the alternator cooler, or is the high idle simply to allow the alternator to make more amps, or some degree of both.....Without data any declaration is conjecture, and useless opinion.

I don't carry much battery capacity but that which I do is a TPPL AGM which is a very low resistance lead acid battery, and it can and does suck up everything my alternator can make when it is well discharged, and my alternator gets hot fast, if I am idling, and it can only make 50 amps at 550 hot engine rpm and about 75 amps at 800, it can't make its 120 amp rating until about 2250 engine rpm, and cruising at 65mph in overdrive is ~1975 rpm.

12.2 amps are required to run just my ignition and fuel pump. The field current sent to the alternator can be as high as 8 to 10 amps when fully fielded, so in order to make alternator amps, 20+ of those are already spoken for, the rest goto loads, and a depleted battery is a big load. A big bank of depleted batteries, not just lithium, is a big load and can overheat alternators easily, especially alternators capable of high amperage rates at idle speeds with owners who place too much faith in their alternator's rating and ability yet have no idea of its temperature.

If one insists on idling parked to recharge, then one better be feeding some cold air to the alternator and not allowing it to ingest underhood heat. The back of my alternator is about 1.25 inches from the exhaust manifold of cyulinder number 2. A heat shield placed here had a huge effect on keeping the back of the alternator cooler.

Some people also put way too much faith in the designers, unaware the designers never intended for the alternator to be feeding a bank of depleted batteries so a van dweller can play on their laptop 8 hours each night and powering a fridge too. If engineers were to design vehicles and their alternators to charge large banks of depleted batteries the larger body alternator would be fed its own cold air tube and be located in the coolest part of the engine where the belt allows it to be mounted and its voltage regulation would be optimized for fast charging with higher voltages held longer, but also be able to throttle it way back if the alternator gets too hot.
Many automotive alternators have self protections built in, basically lowering voltage to the point the depleted battery is drowning with desire for higher amps, yet given a cocktail straw to breathe through.

The alternator can be tremendously effective in charging depleted batteries upto ~80% state of charge, when it is kept cool and told( by the voltage regulator) to produce enough amperage to maintain a high system voltage. Very Few are. A depleted battery can suck up 2/3 more amperage when 14.7v reaches the battery terminals compared to 13.6v. A battery above 80% charged can also suck up 1/2 to 2/3 more amperage at 14.7 than it can at 13.6v but that amperage number is a small fraction of the number when the battery is at 50%.

Lithium batteries can suck more amperage for longer than the best lead acid batteries, but thinking one's alternator is safe from overheating because they are using lead, not lithium, is unwise

I have a K type thermocouple adhered to my alternator casing. The K type thermocouple is what many digital multimeters come with. I have a unit which reads 4 K type thermocouples, and I have one on my alternator, voltaeg regulator, thermostat housing, upper radiator tank, and want one on my transmission output line and lower radiator hose and perhaps differential too.

No need to guess or hope. This time last year I was driving through Texas in cool weather, and my dash coolant temp gauge started reading higher and higher. The K type thermocouple on my T stat housing said temps were normal, and instead of stressing or assuming i was overheating or impending failure was near, I kept going without stress.

https://www.ebay.com/itm/4-Channel-K-Type-LCD-Digital-Thermometer-Thermocouple-Temperature-Sensor-Testers/143450426856?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3Dd3bd8cc4b02e465cb5d3bdc1298756de%26pid%3D100005%26rk%3D6%26rkt%3D12%26mehot%3Dco%26sd%3D264541486704%26itm%3D143450426856%26pmt%3D1%26noa%3D0%26pg%3D2047675&_trksid=p2047675.c100005.m1851
https://www.ebay.com/itm/Arctic-Alumina-Ceramic-Thermal-Adhesive-Epoxy-w-Application-Wand-5g/264501973708?epid=2254438459&hash=item3d958bd2cc:g:4vYAAOSwG8ldqJ6q

https://www.ebay.com/itm/1-FlexFix-Metallic-UL181B-FX-Listed-Film-Tape-48mm-X-109-7M-1-89in-X-120-yd/311786643419?epid=1409872181&hash=item4897ee9fdb:g:FBIAAOSwto5cyyvr

I cover the sensor tip of the thermocouple. which is thermo epoxied to the alternator casing, with 2 layers of reflectix held down with Nashua flexfix. Use rubbing alcohol beforehand to insure adhesion. The sensor reads about 12f higher under the reflectix insulation at 65mph. The rectifier inside the alternator would be a better location for the sensor, but I was not removing the alternator to get it in there.

[TWIH]

Thanks again for reiterating the “using your alternator for charging” points and cautions.
Even if most will never have a 12v lithium battery or a couple (Northstar) paralleled AGM’s, its a good thing to remember that one should not idle for recharging anything, even a golf cart set or (gasp) your own starter battery.

If you have the coin for a lithium battery then pay the extra and figure out how to best recharge it. DC to DC charger, gennie, something other than your never designed for it alternator and wiring.

Do people do it, of course but people do all kinds of not best practice (dumb) things.

[Scott7022]

Great write up and observations. Again I will harp it’s a system. No point ponying up the cash to get into a Russian VIP show lounge if you got nothing left over for a drink and/or lap dance. Factory high output spec or marine rated alternators (I’ve seen people quoting these are better) need to be protected and watched. Custom spec ‘d out high output alternator built to purpose and moved out of the heat run close to 800 bills. High end retail 300. Even for the spec’d out one I’d install sternwakes addition. Great testing sensor.


Sent from my iPhone using Tapatalk

[rvpopeye]

Yeah ^ that temp monitor unit is a great find !

[sternwake]

I don't own that exact temp sensor but one fairly similar. I don't always have it set up, but I keep 4 of the k type thermocouple connectors in my glove box which can reach the unit when I want to see it while I drive. They sell the K type thermocouples upto 3 meters in length, but one can buy longer extension cables.


There remains the issue of what to do if the alternator does get too hot. The Balmar regulator has belt saving and overtemperature features, which essentially dial back the field current and thus voltage and then less amps are required to maintain that voltage, but that regulator is hundreds of dollars, and can't simply be installed in most computerized vehicles.

Honestly many vehicles will not allow any manipulatiion of system voltage or it will fire up the check engine light and then Dc to DC converters are required, and these are generally limited to 40 amps, and might not have any provisions for lowering that transfer if the alternator gets too hot.

The Ideal alternator is one which is externally regulated. I had to trick my engine computer with a 50 watt 10 ohm resistor into thinking it is still connected to the alternator, and I use a transpo540-HD regulator which has a voltage potentiometer. i snipped the legs to this potentiometer, added wires to a 10 turn remote potentiometer on my dashboard. If my belt can't handle the amps my battery and other loads want, I dial back the voltage until it stops squealing. Likewise if alternator temp gets too hot I can dial it back all the way to the point it basically makes no more amperage than what the battery requires to maintain 12.8v or so, depending on its state of charge. I don't really worry abut alternator heat anymore as I don't idle to recharge, but low engine rpms and speeds under 25mph show the maxed out alternator rises in temperature quickly too.

The voltage dial is a wonderful learning tool. Spin a dial and watch amperage required to drive voltage up or down increase or decrease. It kind of removes 99% of the mystery of battery charging. Manual voltage control is now pretty much on almost every device I have connected to a battery. My lights and fans have voltage buckers to increase or reduce their speed, My plug in power supply has an easy adjust voltage knob. My dashboard gauges get 5volts, and yes I have a voltage bucker here too.

Some of my lights and fans have buck/boost modules so I can lower voltage below battery voltage or raise it above. at the twist of my wrist. Modern electronics are pretty amazing. I get 5 of the 5 amp bucker modules for 12$ delivered in a few days. It's certainly taken for granted.

With the temp sensor on the alternator, one can turn the blower motor from speed three of 4,to 4 of 4, and watch it climb 2 degrees.

One does not need lithium batteries to overheat any alternator, not even A HUGE BANK agm'S.
I could overheat my alternator with a single well depleted 90AH group 27agm, but only by idling or driving slow with low engine rpms while the voltage regulator is demanding 14.4v+.

[Blacktank]

one thing i will add is if you have the old style v belt a 150amp alt is more than it can handle,dont have to worry about overheating your alt when you can smell the belt burning

not sure if i will wait for this alt to go bad(maybe a decade)bite the bullet and switch to a 90 amp or convert to serpentine belt but pretty much worthless on a well depleted battery,howls like a banshee and burns up the belt

[sternwake]

A single V belt is certainly limited in max amperage, especially with cold damp pulleys and belts.  Some belt dressing and proper tension can do wonders to attenuate squealing, or increase the output before squealing begins.


More limiting in this situation is not being able to control the field current into the rotor, by having employed an alternator with an internal voltage regulator instead. A simple switch unparallelling depleted house battery is good, but then no charging of it occurs, and then flipping it back on can still cause the hungry battery to try and stop the alternator pulley from spinning

I have a single V belt, and when it squeals I turn my voltage pot down a few rotations CCW to about 13.6v and it stops. Or if my blower motor or lights are on, turn them off.
Then as it dries out and warms up I can crank up voltage to 14.7ish, get a constant unsquealing 95 amps from a single V belt, but it can start slipping and squealing again when slowing down to a stop.
This a 50/120 chrysler alternator, 50 at idle, max 120.

But as pointed out one should not focus on the Ampere Rating, as if the belt slips or a voltage regulator is not seeking high voltage, or  a muititude of other reasons, the rating will never be approached, and the battery is not being charged as fast as safely possible when driving from A to B.
Generally if ones battery is well depleted, fast as possible charging  when driving, is highly desirable, and not being able to influence the voltage regulation, one's alternator can be nearly neutered, and driving 3x as long might be required to reach the same state of charge as an optimized for fast recharging system. 

Some might point out fast charging is hard on the lead acid battery.
I will point out so is overdischarging it and/or letting the next deep cycle begin at a lower state of charge and perhaps much more so.

Regarding alternator fans, I am not sure where the air enters/exits on those with interior fans.  My 50/120 sucks in air from the back and out the front near the pulley and external fan.  I am considering peppering the rectifier plate with the raspberri PI or to220 size heatsinks on mine, keep the diodes cooler, and perhaps more efficien. 
I've also thought abut making a duct cover which clamps over the tailcap of the alternator for a dedicated, perhaps forced air cold air alternator intake,  but I just have never bothered doing so.  Twisting the dial down if it gets towards being too hot, is just so much simpler.  Perhaps if I was carrying around more heavy hungry battery capacity, I would put more effort into it.

There are kits for external recification of alternators, moving the heat source out of the alternator and it having its own dedicated fan.
https://alternatorparts.com/quicktifier-external-bridge-rectifier.html

I've read some reports of disappointed owners of such installations, but I believe they were expecting significantly more output, as opposed to cooler safer alternator running temperatures for more reliability.

[Gr8ful]

I have a serp belt & good fan on the Ambo so I'm good but didn't let it idle to charge & now check the master. I draw 13 amps to run at 70mph.

This is a comment from the article posted Lucian Popescu tkteun • a month ago
Normally yes but we were talking about idle. There are special vehicles used stationary, having high power demand (ambulances, police cars etc)

[Scott7022]

The RedArc manager fifty unit isn't cheap but it is highly rated. Does fifty amp charging. The lower amp versions have been around for a while and I've seen little bad written up in forums or the like. Simple plug and play alternator B2B charger, solar charger, and controller all in one.

The down side past pricey as hell. Is it is one unit for all. Two is one and one is none. Simple failure could leave ya sitting.

Dual alternators dual house bank dual manager 50s. Halfs the work. Redundant and very bloody expensive.

Better other ways to do it for sure. But if you are tall enough and don't want think too much. Not the best way but some folks want or need stupid proof plug and play.