ANSWER: GM CS-144 alternator is best buy to mod

Dual alternators are a must have for the GM 6.5 or to run a decent sized gas production Hydrogen Generator . The CS-144 also called "large case GM" is the best buy to mod because you can easily open it and replace parts with upgraded parts with just four bolts.  The comparison to the AD244 and DR44G requires pressing (or pulling with a puller properly)  the case apart and de-soldering the stator to do rectifier mods.  The one value to those designs is you can snap off the rear plastic cover to change brushes easily.

Often you will find information to the effect "If the battery is not in good condition, the alternator will be overtaxed trying to charge it and this will shorten the life of the alternator."  Well this is misleading because a battery not in good condition means usually a shorted cell or low on electrolyte, then yes, but if your vehicle needs more electrical load than the alternator was designed to put out, that means the alternator is just undersized.  A good example is a RV or Marine scenario, where there is a starting battery and internal utility power batteries.  When the vehicle is started after the internal batteries have been run down a bit, the alternator voltage regulator will sense the need to charge, and the starting battery will resist overcharging and allow the extra current to pass onto the interior batteries until they come up full.  This will shorten the life of the alternator if it has to max out for a long period of time thus getting hot - which is the definition of "overtaxed".

Any alternator only produces the amperage required to maintain the desired voltage controlled by the voltage regulator in the alternator.  Therefore, if we take a stock 120 amp alternator off the car and replace it with a 360 amp alternator, it may never put out more than something like 100 amps if that is what the various devices in the car are pulling from the electrical system.  In other words, it does exactly the same job as the stock alternator, and no more.

Looking at the drive end as the pic above shows in profile on the side of the left mounting hole are usually GM  particulars dot etched with the last of the top line reading "124A" or "140A" and that is the confuratikn the alternator was built originally as.  While it "might" work, on a dual setup you should avoid mixing the 124 amp and 140 amp rotors.   The experience has been seen that the 124 amp will not start to put out at low rpm - even with an over drive pulley.  Then the slightest rpm increase results in it jumping in shutting down the other alternator instead of them "following each other.    Using external Ford style Transpo F540XHD regulators this can be noticed by touching the two and one will be warm and the other cold.  When they follow they are both uniformly warm.  If you have a gauge it may bounce slightly.  Recently the bouncing increased which is a sign of worn brushes.  When opened the commutator ring was worn with grooves which is another sign one alternator was working harder than the other.  The housing rotor assembly was swapped and new brushes installed.  When started the alternator snapped to immediate 14.2 volts steady.  It previously would slowly go through 13.8 volts eventually reaching 14.2 in a minute or if rev'd slightly would bounce up and if idling below 640 rpm  would drop to 14.0 volts under load like fan and headlights.  After the replacement to the matching 140 amp rotor it holds 14.2  rock steady under even a heavy load with an inverter running a microwave at even 600 rpm - which is a warmed up engine - good fuel rpm on a 6.5 GM Diesel.  The engine can be heard under slight load as the alternators work together to share the increased amp draw.  Previously before the dual alternator setup was installed, the unit had an automatic high idle kick on in such a condition at idle which is shut off by tapping the brake pedal like shutting off cruise control.  It does not activate anymore after the dual alternators were installed unless cut on manually - like to perform a boost to another vehicle or running the 40 amp inverter pure sine with a 110 volt welder plugged in.  The 124 amp rotor apparently has a few less windings. 

For instance larger GM vehicle like  Buick came with CS144 alternators that are capable of delivering 120 amps if needed. The factory matched this alternator quite well  and it can handle the load in most instances. Factory specs are around 75- 80 amps @ idle (750-850rpms) during normal operating temps and 120amps at 1800 engine rpm (55-60mph) cruise.  

To get an alternator to put out more amps you have to LOAD it. Then it will charge lower than average batteries.  There is an expensive  marine product that does just this to create a load to make an alternator charge the onboard interior batteries while motoring, and will cut off when the battery bank is fully charged. See

This is a good place to state that amperage specs for alternators are normally shown versus alternator shaft rpm.  Given that the alternator pulley is smaller than the crank pulley, the alternator is turning faster than the engine rpm.  This ratio may vary from car to car, but, the normal ratio range is usually between 2.5 and 3.0 to 1.  For a car it is close to 2.8-1 when one takes the time to measure the diameters of both.  This means an idle speed of 800 rpm will produce an alternator shaft speed of ~2240 rpm.  Keep this in mind when looked at the graphs provided by the alternator manufacturer and don't be misled by claims otherwise. See the CS-144 alternator graphs below.

Also note that the best alternator in the world will not over come wiring and connection problems.  Bad grounds, corroded connectors, loose connections, too small a wire size, broken strands, etc. can all make a good alternator to be seen as bad.  The first best thing one can do is replace the alternator cable with a 4 or or 0 gauge  battery cable to the battery.

Further, many places are not set up to test alternators properly and an alternator that passes the test down at the parts store may not be as good as the store tells you.  For instance Autozone cannot test anything but a stock alternator by car - and the tester will register a fail on anything else like a modified alternator.

Many stores do not have a proper load test to correctly check an alternator.  In other words, they check the voltage output when spinning the alternator and it checks out good.  But if they had a load tester that would apply 100 amps to the alternator, they might find the voltage dropped to under 12 volts instead of hanging close to 14 volts as it should.  For instance a Carbon Pile load tester is used to do this and some places cannot test over 100 amps anyway.

It is not unusual to buy a replacement alternator that is no good from the get go, either, or it is a rebuilt with lower amperage than the box claims.   Even some alternators that are new rather than rebuilt can fail to be good as they are built overseas with less than great quality parts.  So if you have a CS-144 - you can build or rebuild it yourself with common hand tools in a few minutes.

Normally, an alternator that is failing will start to lose voltage at wide open throttle in the last part of the run as the electrical regulator inside gets hot and lose control of the regulation.  If you have a gauge and the needle bounces, it is a sign the brushes are failing.  If you are sure that the wiring and battery is good, then it is time to find someone that can apply a proper load test to the alternator.

Heat is the biggest enemy of the alternator and you will probably notice that quality high output alternators that are used on serious sound systems have externally mounted rectifiers instead of having them inside the case...and, they may have two.  

Now, let's look at the graph provided by Delco for its CS series alternators.  As mentioned before, this graph depicts amperage vs alternator shaft rpm and not engine rpm.  For most cars, multiply the engine rpm by 2.8 and use that number on the X-Axis of the below graph.

These curves show amperes vs shaft rpm at 14.0 volts.  Our stock alternators are of the first generation CS144-120 amp variety.  The 140 amp alternator came out in 1992 and is a revised alternator improving on some of the weaknesses in our units.  This is my suggested replacement.  Not because it is higher output (significantly so at idle) but, because it is just a better all around unit and is a direct replacement for ours at

Two thing affect alternator output capability - the stator winding - being a quad wound one needed for highest output, and the rectifier didoes - where you ADD the number of Diodes max output ratings one half the rectifier to get max potential output capability.  For instance  a 12 diode rectifier with 80 amp Diodes is 6 times 80 which is 480 amp capable output.

Looking at the above graph and taking the the 2.8-1 multiplication factor into account, we can see that a properly working 120 amp alternator should be putting out approximately 75 amps as stated prior.  This means that the battery will supply additional required amperage as it was designed to do if the requirement is above 75 amps at idle.  This should be adequate, and if your car is pulling a bit more than that, the battery will fill the gap.  Another way is to increase rpm at idle with a smaller pulley but that means you need shorter diameter  belt.

If you are in the habit of standing still for extended periods of time with a good sound system cranked up, then you may well be a candidate for a higher output alternator as the factory unit is going to be working hard to replace the power pulled from the battery when you do drive off.  Your voltage reading will tell you if the alternator is struggling by reporting lower than normal voltages. If you are more typical and the above scenario only occurs at stop signs during rainstorms at night with the sound cranked up, then not enough time elapses to cause a potential problem.

 Remember that most system specs are rated near maximum volume and you may not normally operate in this range.  Still, it is wise to do some research and determine exactly what is suggested for similar set ups and plan accordingly.

If you already have a CS144 - upgrade it with a 200 amp stator (quad wound) and at minimum 60 amp diodes or a 12 diode improvement like ours

In 1992, GM made some revisions to the CS144 series and added a new model rated at 140 amps.  See the above graph.  Note that this unit is capable of approximately 105 amps at 800 engine rpm (~2240 alternator shaft rpm) which some 30 amps more at idle than our original units.

This unit was installed on at least the following cars:

1996-94 Buick Roadmaster 5.7L, 1996-93 Cadillac Fleetwood Brougham (RWD) 5.7L, 1996-93 Chevrolet Caprice 4.3L& 5.7L, 1996-95 Chevrolet Impala 5.7L, 1995-92 Chevrolet Lumina APV Van 3.8L, 1995-92 Oldsmobile Silhouette 3.8L, and the 1995-92 Pontiac Trans Sport 3.8L  You can look for these in a bone yard to find a core to build.

This alternator was also installed on police cars, and fleet vehicles such as taxis where normal operation may include lots of non-moving use with heavy radio traffic.

 It is listed as a Lester no. 8112 which may be helpful at wrecking yards, or such places.

Given that the price of a brand new unit is not much more than a factory 120 amp replacement, I believe this is the logical choice when replacing a bad factory unit.  My first preference would be to check with Pick-a-Part and see if I could get one for $50, or less as most should have several years of life left and parts are readily available for a rebuild if, and when, it needs it.  This CS-144 Alternator is easy to rebuild.  That should be kept in mind.

Make sure you understand that a 300 amp magic alternator does not put out any more amps than a factory 120 amp unit unless the car has something installed that demands the power.  Alternator rating is meaningless unless there is something installed that will actually pull the current.  On a normal car with normal equipment, the only thing that a mega-huge alternator does is create a large draw on your bank account.  However if you are running a Hydrogen Generator that can draw substantial amperage.

Now let's finish with the exotic ultra high amp alternator systems. We all know they are commonly used on ambulances, emergency vehicles and 2000 watt ricer stereo systems.

 Emergency vehicles before the open frame AD244 or DR44G used special CS 144 units with external extreme duty dual rectifiers to handle the load. This is on 250 amp or higher alternators.  This is where 12 Diodes and Heavy Duty external Rectifiers are needed.  Also today if you run an AGM battery you want to change from the 14.7 volt regulator to a 143 volt one, and your best best is dual alternators - PERIOD

The reason is they will return the batteries to as full a charge as possible - FAST - depending on how the alternators are set up and /or the second alternator is needed to handle the load of the Hydrogen Generator.  Stock alternators with the internal regulators will not do as good a job as commercial external regulators - and at least one external regulator on the market can control both alternators itself.  Recommended is the F540XHD set to 14.3 volts - a Ford part - it is adjustable if the rear cover is removed there is a potentiometer adjustment found there exposed in the pot covering the electronics. . Be sure it is a F540XHD from 'Transpo usually - the others do NOT have a voltage adjustment and are usually set to 14.7 volts.  One wire goes to the excitation wire to the alternator - one wire is 12 volts hot at all time - one wire is field and the other stator.  A video is at and here =>   Note that for the AD244 or CR44 no non-avalanche diode rectifiers have been found on the market - so for welding the CS-144 is the only option. Setting up the AD244 and DR44 is the same however for field and stator output through the case to an external regulator. If you have an RV or work truck with an inverter, dual 240 high amp alternators properly set up on a commercial regulator (Taxi - Limousine - Ambulance - Police - RV) system can easily power a small microwave even at idle without drawing on the batteries - and in fact will continue to charge them

A CS-144 can be upgraded to a 200 amp unit with a new 200-240 amp quad wound stator and DR5180 rectifier with 70 amp diodes and a 2 inch overdrive pulley.  An AD244 OEM actual DELCO  needs just a DR4402HD-3 rectifier to make it a 240 amp output unit, and DR44 series Chinese made alternators  can either have the rear housing changed to a DR3580HD-3 with 80 amp diodes - or you can rebuilt it using 3 NTE 5935 and 3 NTE 5934 new press fit 75 amp 400V Diodes .  In both cases you need to de-solder the stator.  If with the DR44 family you will need to split the rear case off  If you cannot see the stator between the two halves of the alternator it is a 230 or 130 unit and you need to replace those as they  are not worth the work and they will overheat.  It should be noted that the DR44 has a way to use 12 diodes by drilling the case and converting the mounted rectifier plate so in theory it could pass 450 amps maximum.

Setting up the alternator as a commercial charging system is not hard in the GM CS-144 and 244 - one simply breaking the stator and field connection - at the brush heading to the internal regulator and adds a wire to each that goes outside of the case.  The wire on the regulator side is the "stator" and the one on the brush side is the "field",  Then the exciter wire normally to the regulator goes shared to the commercial regulator (it would be the one that is wired to the key on of the start and run) and there is a hot wire from the battery, and the regulator must of course be grounded.   One of the easiest ones to get and use is the Ford style F540XHD and if it is opened, one can see it is "potted"; however it has a small adjustment resistor point exposed to turn it up or down.  It is set at 14.2 volt - but will go - unaltered as high a 14.4 in a dual alternator configuration without damaging an AGM Battery.  See also

Certainly one way to combat this is to use more than just two large CCA rated batteries and better yet high CCA rated AGM batteries only, but if you have dual alternators your batteries will return to full charge as fast as possible because they can deliver higher amps to recharge them in a faster time period and it will extend their life