Higher Power Alternator for My Car

Volkswagen Jetta High Output Alternators - Quality Power

Fix a PV on the roof of the car and charge the same or bigger or separate battery

Where can I get a PV that outputs over 100Amps at 12Volts that will fit the roof of MY volksvaggan?

Why not just go all the way....

I have a 2000 TDI MK4. I don't use an alternator at all, instead I rely on two marine batteries (available cheap at Walmart) in the trunk. I have a low amperage (1.5 amp) charger that I plug in in the evenings. I can drive 12 hours even overnight without running out of juice.

You can probably keep your alternator running and just install additional battery capacity. It is much cheaper to charge your batteries with an efficient wall power based charger than relying on your automotive alternator.

Out of curiosity...

Did you do the math to determine HP savings vs. fuel efficiency (weight gain)?

This is a serious and not smartass question. I have thought of doing this before, too.

What exactly would you be expecting to gain here other than the increased chance of getting stuck someplace without enough battery left to start the engine?

I've driven from central Florida to the Virginia coast with a good portion of the trip after dark (so headlights are burning) several times without problem.

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Its funny but the whole battery modification has made me more aware of the increased inefficiency of large amperage draws (I didn't initially add sufficient additional battery reserve, merely doubling the stock battery).

Even though I now have enough capacity to drive to Virginia at night without battery problems, I still park on a hill when it is convenient and have become very skilled at very low speed, smooth rolling starts.

Even if there isn't a hill, if it is flat, I can push start my car without too much effort (the secret is using 2nd or 3rd gear, and only engaging the clutch for a moment before re-disengaging, so that the engine is free to start without being restricted by the speed of the vehicle).

That has to be one sad little underpowered engine if the loss of a half a HP for the vehicles electrical load is worth 15% fuel mileage increase!

Fuel expended on turning the alternator is significant in pretty much every modern car. Estimates of percent of fuel used on turning a modern cars alternator range from 10% to 20% typically.

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The TDI engine is one of the most efficient engines on the road today and has been for more than a decade.

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With things looking so sad (comment #12) and miserable (comment #9), it makes me wonder if you have forgotten to refill your prescription....

I can't see how those numbers could possibly be true. Given a 100 amp alternator like the one on my Ford F250 can be ran at full output from any typical 4 HP lawn and garden engine even when spinning it at a 2:1 gear up of 7200 RPM.

In the EV world a average full sized sedan takes less than 500 Watt hours of energy per mile at 60 MPH that works out to a rough power demand of around 30,000 watts per hour to move the vehicle. Assuming even 10 percent of that was to drive an alternator that would mean that the alternator would be having to draw at least 3000 watts of mechanical power or 6000 watts at 20%.

To take the assumption even further and allowing for a dismal 50% alternator efficiency that would still give you roughly your 100 amp continuous output at 14.4 volts and the rest going to heat which is highly unlikely being the physical components and size of a 100 amp alternator are not large enough to dissipate some 1500 watts as pure heat energy.

Now going by your references I would assume that the two Walmart deep cycle batteries where the largest ones they carry which are around 110 AH 12 volt units.

Going from that they would have a theoretical combined power storage of roughly 2640 watt hours. Now if they can sustain your car for 12 hours without going dead that would imply that your cars electrical system has to draw less than 225 watts or about 18.5 amps average load.

Also if you can recharge your batteries overnight or even in less than 5 - 6 full days after a 12 hour run using a 1.5 amp charger you are using far less than 225 watts per hour of driving.

Now if 225 watts per hour is taking 10 - 20% more power than just moving the vehicle you must have a very small and sad little engine being that if 10% of its power is 225 watts you have a mechanical engine power of roughly 2250 watts or just about 3 HP or 1.5 HP if it's equaling 20% of your engine power.

Like I said the numbers are not adding up here. Either you have a very small engine or something else is going on to get the numbers you are claiming and right now I know from first hand hands on experience from playing around with AE that there is no alternator that puts out 100 amps or less that takes more than 3 mechanical HP to run at full load.

You are exactly right for steady state driving. The alternator would probably easily be less than 10% of the draw. But real world driving isn't steady state. In fact in many driving conditions, more time is spend off the throttle than on.

The big part of the story that you are missing is when the alternator is pretty much the only load.... like when otherwise coasting, or when sitting at a stop light.

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The engine in these cases would be burning almost nothing, but the alternator is making it work to turn the fans and recharge the battery.

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And considering where engines are typically least efficient... at partial throttle at idle, it really isn't that difficult to understand how an alternator can be responsible for even 20% of fuel consumption.

Actually, I saw an immediate and substantial improvement in MPG efficiency. It is by far the largest single increase in efficiency I have been able to make.

The MPG gained was over 15%. That is not a best tank value. That is the minimum gain over the averages of several tanks.

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Even with the inefficiencies of the charger, charging the battery and discharging the battery, I come out way ahead. The wall power cost a few bucks a month.

Fascinating: What does the computer think of this? Does your CEL remain lit?

Yeah the CEL pretty much stays lit. The EGR valve is disabled (another noticeable increase in MPG, but additional precautions need to be taken, so I wouldn't recommend it to anyone who doesn't have a good understanding of how that can affect the engine) and glow plugs are disconnected (I live in a warm area and start-up is always immediate).

Do let the car's insurers know that a modification has been made, as it may affect the premium payable to cover the changed risk. Were the vehicle to be involved in some sort of incident and the insurer were to find out that the vehicle had been modified, then it might be the case that the insurance cover is invalid, and that's not a good place to be.

Gosh it must be a miserable life living in constant fear of what your insurance company may think if something as mundane as replacing an alternator with a better one is worth concern.

It should not be possible to burn out the diodes with a relatively small increase in load - alternators are current-limited. Diodes are more often blown by attaching a mains charger that causes spikes.

Estimated extra load: small fridge (Peltier) say 5A, laptop computers say 5A each. Total 15A extra. That's only about 15% of the alternator's capacity. You could try measuring it to be sure.

The problem might be the time you spend idling. With A/C fan, lights etc plus your extra load, it may exceed your alternator's idle-speed output current capability.

Assuming your alternator is in good working order (no worn out brushes or bad diodes), a simple answer would be to devise a mechanism to raise the idle speed when required. A voltmeter will indicate when it is needed - perhaps at any voltage less than 12.5 .

A manual device like an old-fashioned 'choke' pull might be used, or an automatic one. Delco used to make a relay with voltage detector that was used to shut off the rear window heater, seats heaters etc under low voltage operation. Perhaps such a unit would enable you to activate something like the idle-increase mechanism that is used when the aircon is engaged. Needs some hysteresis to avoid 'hunting'.

Good luck!

At first, to increase the alternator Amp rating is a good start. This we also did when we designed a power supply for a DTV test car.

But more important is the second marine style battery for the computers and the fridge.

The battery should be charged from the alternator via a loading current splitter. Formerly these where diode based but now better FET operated units are available. Also sense making is a battery switch to disconnect the battery in case of non-usage.

It is a good habit on every boat or camper van to differentiate between starter battery and the "equipment battery" to avoid the fact not to be able to start the motor again.

But during the a.m. project we found another way to extend our battery life. We were using in the car standard test signal generators, TV monitors and laptops. So in the beginning we had a 2.5KVA inverter on board to supply all the aux equipment. We were a bit surprised about the short battery life of our 180Ah battery. That was because a relative low efficiency of the inverter if the 2.5KVA where not full utilized.

So in case when we used only the TV monitors and a laptop we switched off the 2.5KVA inverter and used a 300W inverter instead to extend the lifetime of our battery.

Considering the drive to the tests where the battery was disconnected but charged via the diode splitter we always had a full battery available and seldomly needed to recharge the battery in our garage for the car.

LET'S BREAK THIS DOWN.

First, you need more/bigger battery. I suggest a sealed lead/acid. Can give huge amount out when needed, AND can be charged at basically anything your car could produce. i THINK A BANK OF BATTERIESIN THE TRUNK WOULD HELP A LOT. This would mean a slightly fat pair of cables to the area, but would pretty much solve a lot of your needs. This should be paired with a boat style battery state-of-charge meter. Then if your draw is larger than the current alternator/ engne speed output, and the battery (s) have low amount of reserve left, it is time to up the rpm's and or reduce the loads.

Living on a crusing sailboat is similar. I did.

Then alternator. several types come to mind, go to a big boat store and look around.

I think if you use an independently mounted diode bridge ( fan cooled) then the alternator might be bigger that would fit now. Alternators need high RPM'S to put out what they can really do.

See if you could change the pulley on the alternator to smaller and thus get it's speed pushed up.

See if you can get bulbs that are more efficient LED's.

fred

The comments in the notes I am replying to are on target and raise actual answers to some of the issues. I will make some more comments. Some are actually pertinent.

The underhood temperatures around the alternator will be in the neighborhood of 250F on a VW with a high ambient temperature. I live in the Southwest, 104F is considered cool! Look at some of the alternators used for the Eurovan or Rialta and you might find a higher rating that might fit. The use of higher rated diodes is always possible and the windings might be able to have a wire size increase. Talk to independent shops that rebuild alternators and modify them. A typical GM 140 amp alternator can be raised to easily above 250 amps. A firm in Texas goes way higher but it is pricey.

Look at your loads. You say refrigerator, what kind. They are not all equal. I have a Vixen motorhome that uses an electric refrigerator and has no generator. It is very efficient but old. I purchased a popup pickup camper also and changed the icebox to an electric refrigerator. When I looked at the power draw on refrigerators, I had to go to a marine grade refrigerator that retails for over $1500. Although I got it for a little over $600 it was still quite pricey for me. The little boxes from Walmart or Sears just don't cut it. Be sure the refrigerator is not just adding heat to the interior of the vehicle or you may have to run you AC on high to compensate and that adds a power load for the fan.

The other loads that we run into on our vehicles are computers and lighting. Both my wife and I use computers and other electronics a lot and with the camping type vehicles we use a lot of lighting and computers in the evenings. Laptops are much more efficient than desk models but some still burn up a lot of power. Many times we found that the plug in power supplies use the same power whether the battery is being charged or not. What we have settled for was purchase of a newer but not current Apple model for my wife that is particularly noted for low power consumption and we plug and unplug the charging cord at the 110 to bring the battery to full charge and then run off the batteries. Our inverters were picked for high efficiency. My choice of computer is MS and I picked a really outdated convertible tablet that is very efficient energy wise but has a very small battery. I find that I usually have been keeping it plugged in but it has an energy efficient charger. We have looked at the IPAD and Android and actually have the later, but since they are not real computers (my windows phone can do more than they can and it is really dated) it is not feasible to carry them in a limited space environment. I will say that they are much more energy efficient. Some of the newer windows tablets are looking good. The other tablets (ipad and android) are good for games and light programs but not serious computer work. As time goes on and real applications are added that may change, but right now they won't even work alone with most printers.

We have converted all interior lighting to LED. That is a big power saving.

One last thing, My vehicles both ran headlights during the day time for safety. My truck was able to be programmed to run the running lights instead which could be changed to LED. I am in the process of doing wiring to accomplish this on the Vixen also.

We have a number of Vixen owners in our VOA organization who use their vehicles as portable offices and do quite well. They particularly like having the "facilities" and microwave available. They have found innovative ways to save power. They never get the mileage your vehicles do, but 32mpg isn't all that bad. I personally have 400 watts of solar available also but will be increasing that to 600 soon and that helps when not driving.

The use of sealed lead-acid only have an advantage in that they are better if the battery is not in a ventilated area. Flooded lead acid are better space and weight wise for the equivalent power, but must be vented to eliminate explosive gases. In my Vixen I have opted for LIFEPO4 batteries (360 amp hours) but talk about pricey!

I will make a comment to some that think that the Alternator takes a lot of power. I have not seen that. I have a very high output alternator and have run some heavy loads from it when camping. (I have allowed my daughters Rialta to plug in to 110 from my inverter to be able to run both microwaves and all other items when her batteries failed) I am an EE and most alternator designs are reasonably efficient. A 140 amp load at 14.4 volts (if it ever got to that) is 2.8 HP and if you add 20% for belts and inefficiency (which is high) you get about 3.33 HP which is certainly not the 15% load on the engine that some have sited. I have monitored fuel flow with the batteries charged and no amps and with the batteries almost out and inverter and microwave use and over 100 amps from the alternator. The increase in fuel flow rate is too small to detect. It is a diesel, but still, just turning over the engine takes quite a flow at idle. The alternator seems to have no effect on it. I have not tried the same experiment on my gasoline powered truck yet. I did that on the motor home to justify the added solar panels. Yes, they will pay for themselves quickly. I will then not ever have to idle the Vixen when I camp "dry" for extended periods.

"A 140 amp load at 14.4 volts (if it ever got to that) is 2.8 HP and if you add 20% for belts and inefficiency (which is high) you get about 3.33 HP which is certainly not the 15% load on the engine that some have sited. I have monitored fuel flow with the batteries charged and no amps and with the batteries almost out and inverter and microwave use and over 100 amps from the alternator. The increase in fuel flow rate is too small to detect. It is a diesel, but still, just turning over the engine takes quite a flow at idle. The alternator seems to have no effect on it."

Yep same observations here as well. We have a number of old tractors and vehicles we use around the farm that I have converted over from generators to modern Delco 10SI 60 - 100 amp alternators and with everyone of them the good old amp meter tells the whole battery charging story very well.

Start them up and the amp meter says they are taking 30 - 40 amps to charge the battery but for maybe 20 - 30 seconds where at that point they drop to zero or very close to it. Also being open frame tractors it's easy to just reach in and put a hand on the alternator to see ifit hot or not and not one of them warms up unless there is an actual high current load being drawn. No load = no heat = no added drag on the engine.

Same with the big tractors that are diesels with the 100 amp alternators, two big batteries, eight 60 watt halogen lights, AC, cab fans, radios, and other electrical accessories. Start them up and they draw high amps for about 30 seconds to a minute while the batteries come back up then drop off to near zero again even with all the added loads running. With all the added loads on their alternators run warm but nowhere near dangerously hot to touch.

My point is if there is no high power load the alternator has nothing to do and thusly does not draw any extra mechanical power from the engine.

If a person is curious as to how much power their alternator is putting out its easy to simply wire a common dash mounted aftermarket amp meter or commercial shunt meter right in series with the alternators main power lead and see exactly how many amps its needing to put out at any one time. Odds are unless you have a lot of added loads on the system the average output is not going to add up to much power wise compared to what the engine puts out even at idle or part throttle.

--800-1000 RPM idle speed for Jetta TDi

--50% to 60% efficiency for alternators

--3 HP to run an alternator at about 700 W

--Jetta TDi makes roughly 30 HP at idle

--10% of the produced HP is used to power the alternator

--As engine speed increase (vehicle speed) more HP is required to simply move the car leaving less power for increased coolant flow, air conditioning, etc. The remaining power produced by the engine goes towards the alternator as well, which has the increased load off-idle for fans, accessories, lighting, etc.

-The alternator load will continue to be around the same level for the average driver, not the hyper-miler.

Some good ideas here, well worth thinking about.

My suggestion is to first make sure that the alternator is not pulling current when the engine is stopped, easy checked with a clip on ammeter.

Secondly, add a small 12 volt fan (or two) to suck air through the alternator and thereby keeping it coo, waterproof ones would be good, run via a thermostat would be best.....

The other ideas may be not needed, though I do like the extra battery idea a lot....

Remove the six diode bridge from the alternator and let the three wires from the stator exit the alternator housing. Install a bridge using over sized diodes which is external to the alternator. The bridge could be made from large stud mounted diodes.

• The diodes should never fail if they are over sized for current and reverse voltage and cooled with a heat sink.
• The heat produced from the forward drop of the bridge is now outside the alternator.

Since the stator is now the only element producing heat within the alternator body, you'll be able to get more capacity out of it. And to boost it's capacity even more, provide some cooling from an external electric fan blowing directly on the housing or duct air to the alternator.

GA

Someone is thinking outside of the box!!!!

It would appear that way at first but in reality it's more than likely you would lose more than you gain.

The typical automotive alternator uses Germanium or similar low forward voltage drop diodes. Most test at around .4 - .5 volts at their full rated current.

Now also alternators are three phase devices so at any moment there are no more than three of the 6 diodes conducting plus the total DC amp output averages out as being only 1/3 of the amps coming from each phase which means that in a 100 amp alternator at any one point you have no more than three diodes conducting with an average power loss combined of around 50 watts out of a system supplying some 1400 watts.

Now the problem is if you go with external stud mount type diodes that odds are they will be the standard silicon type with a .7 - 1 volt forward voltage drop at full output which now means your external diode system is now wasting more power than the stock one inside the alternator did meaning you not only gained nothing but you actually lost usable power for your efforts.

If the OP needs more alternator power his is best off either working with the knowledgeable people who build up vehicle electrical systems for high powered audio applications or to go with refitting a better alternator from another type of vehicle.

It should be possible to obtain diodes that at the modest rating of 140 amps will have less than .3 volt drop. I think that external diodes are a better way to go, along with an external voltage regulator, but it would do well to rewind the alternator with better windings, increase the voltage capability slightly with more turns and increase the wire size to give more amps. A little help on the cooling wouldn't be bad since it is a VW design. The diodes should be well oversized to reduce losses since they don't go up in price proportional to amps so they will never go bad. The hockey puck design is cheaper but you spend more for the mounting. I remember having to polish those things into the heatsinks and it is a pain.

It could be done but if you don't know anything about rewinding alternators or about the details of the how and whys and where to find the specialty parts they are rebuilt with for higher than stock power outputs, which very few people do, there is no point to the endeavor.

Especially when a factory built high output unit with a warranty can be had for not much more than the stock unit costs and you know its going to work the way it is supposed to right out of the box.

That is a great idea (I hope). As I am beginning to just doing exactly what you are suggesting to an older car ('92 Saturn SL2 with ~120,000 miles) that has "fried" the 6-diode bridge (rectifier) far too many times - usually every 3 years or less, during its 21 year life. I suspect thermal issues and possible thermal shock (water splash protection is probably marginal in factory location down at the oil plan level and adjacent to the front right tire.) I am using a pre-built kit with two external 6-diode bridges (in parallel) and small cooling fan. I will relocate it in an area that is away from water splashing (thermal shock) as the actual alternator is sandwiched near the oil pan and right front tire. This website link takes you to the remote rectifier. http://alternatorparts.com/quicktifier-external-bridge-rectifier.html Sorry for the text link; I am editing this in an old version of Safari.

Per my post, here is the proper link and a photo for the remote diode box known as the "Quicktifier". I chose the 420 model, as it has 2 rectifier units in parallel and is suited to the heaver amperage loads.

Link: Quicktifier Link