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Old 10-18-2007, 11:20 AM
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Increase Alternator Amperage

Is it possible to increase the amperage of an alternator aside from buying a new one?

My '76 K5 Blazer has a 54A (fairly new, stock replacement) alternator. I have installed a Mark VIII electric fan & and some 150W KC's. If I am running the fan and just the headlights the volt meter drops to about 10v at low rpm (<1300). Once the RPMs go up it will stay around 13V. Recently at the coast I did quite a bit of low speed driving in the fog. When I shut down for a couple of minutes the battery was dead (Optima Red). Had to jump it.

When on the dunes with everything on (headlights high, KC's & fan) the volt meter will not go above 12V.

If I am sitting at a long light with the headlights and fan on, the volt meter drops to about 10 or possibly less. I sometimes think I can feel the engine start to stumble. I have gotten into the habit of taking it out of drive when at a light at night. I will sometimes shut the fan off if the weather permits (when at a light - watching the temp of course).

Is there something in the alternator that I can replace to increase it's amperage or will I need to buy another alternator?

Fan and KC's are relayed to the battery/ground.

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Last edited by 70bird; 10-18-2007 at 11:39 AM.
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Old 10-18-2007, 07:54 PM
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Technically, you could install the parts to increase the amperage output to your current alternator, which would include replacing all of the major components, such as the stator, bridge rectifier, brushes, etc., but the higher amperage would only be available when the engine is making moderate to high rpm's.

Your current alternator can not output enough amps to run all of your additional accessories, thats why you are seeing such low voltage readings, your battery is also trying to supplement current for the lack of output by your current alternator, which is why you are experiencing a dead battery after driving.

For your application, you need to change alternators and install a GM CS130 or a CS144. The CS130 comes in several versions, but 105 amp is pretty standard, I'm running a 130amp version in my street rod. The standard version of the CS144 is 120 amps. The CS130 or the CS144 alternators output a higher amperage at idle conditions, which is what you really need to solve your current electrical needs. These alternators also have dual cooling fans to prolong the life of the alternator.

There are several websites that explain the conversion between the alternator you have and as CS series. Here's a couple I had bookmarked:

http://www.novaresource.org/alternator.htm

http://www.chevelles.com/techref/ftecref14.html
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Old 10-18-2007, 08:11 PM
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Another option is to try a 94 amp 12si alternator (your current alternator is a 10si). I switched to a 12si on my '75 K25, and it made a significant difference in keeping the voltage up to about 13.5-14.0.

You can get a 94 amp 12si for your truck from any auto parts store. If you get one with a V-belt pulley, its a direct bolt-in to replace your current 10si.

The only other change you need with a 12si is to run an 8 gauge charge wire (with a 12 gauge fusible link) from the B terminal on the alternator over to your battery.

The CS alternators will put out more amperage, but the conversion is a little more complicated.

Bruce
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Old 08-30-2009, 02:20 PM
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Increasing Alternator Output

Ah this old chestnut keeps on coming around again and again however you may be able to improve matters by fitting a smaller alternator pulley. If belt slip then becomes a problem it is possible to increase the angle of belt wrap by using an idler roller or two and a longer belt. (A greater angle of wrap around the pulley is better than having an overtightened belt). As to advertised amperage ratings, in general this is the 6000 rpm rating (alternator rpm not engine rpm). When the alternator is only turning at 1500 rpm there is not much output. 1800 rpm is needed to achieve "idle output" which is typically a third to a half of maximum output. Top class alternators can withstand 20,000 rpm briefly so for engines that rev to 6000 maximum a 3 to 1 speed-up ratio is about right. For diesels 4:1 is worth considering. Whilst bigger and better alternators are very good to have, it is still necessary to spin them fast.
Another way if one has a vehicle with a spare groove on the crankshaft pulley is to fit a second alternator. This dodge is commonly used on boats where engines often tick over slowly. Back in the "good old days" before quartz-halogen bulbs and alternators were invented twin dynamos were popular for night rallies in England. (Parallelling dynamos can be quite tricky but parallelling alternators is no big deal) Good luck.
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Old 08-30-2009, 03:51 PM
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Quote:
Originally Posted by Davey1000
Ah this old chestnut keeps on coming around again and again however you may be able to improve matters by fitting a smaller alternator pulley. If belt slip then becomes a problem it is possible to increase the angle of belt wrap by using an idler roller or two and a longer belt. (A greater angle of wrap around the pulley is better than having an overtightened belt). As to advertised amperage ratings, in general this is the 6000 rpm rating (alternator rpm not engine rpm). When the alternator is only turning at 1500 rpm there is not much output. 1800 rpm is needed to achieve "idle output" which is typically a third to a half of maximum output. Top class alternators can withstand 20,000 rpm briefly so for engines that rev to 6000 maximum a 3 to 1 speed-up ratio is about right. For diesels 4:1 is worth considering. Whilst bigger and better alternators are very good to have, it is still necessary to spin them fast.
Another way if one has a vehicle with a spare groove on the crankshaft pulley is to fit a second alternator. This dodge is commonly used on boats where engines often tick over slowly. Back in the "good old days" before quartz-halogen bulbs and alternators were invented twin dynamos were popular for night rallies in England. (Parallelling dynamos can be quite tricky but parallelling alternators is no big deal) Good luck.

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