Voltage too high??

[another69]

The electrical system in my '69 is pretty basic, and has been very reliable, but today I noticed something odd. While driving around, I noticed my volt gauge would spike to 16 or 17 volts, than back to 14. I noticed it doing this several times. Sometimes it would stay at 16 volts for a few seconds, other times for a split second. It did not seem to be dependent on RPM, but did seem to happen more often above idle. I was not able to confirm the reading with a multimeter. I have an internally regulated alternator conversion. Is there anything external to the alternator that could cause this?

[GeoffP]

Is it an original externally regulated charging system? If so, it sounds like you've got a voltage regulator failing.

[another69]

Yes, originally externally regulated. Now internally regulated with a jumper replacing the original external regulator. I am using a rebuilt 7 year old internally regulated 3 wire alternator (10SI 65 Amp I think) that has a 10 gauge original charge wire going to the original horn relay. Can anything other than the alternator (now that it is internal regulated) cause excessive voltage? If it is the alternator I will likely replace it with a 100 amp unit with a larger charge wire etc. I would like to use an alternator with an internal fan if possible.

[another69]

I hate to put in a new alternator if its ok, but its hard to check because its intermittent. Could it be anything besides the alternator now that its internally regulated?

[GeoffP]

Yah it's likely the internal regulator. I had mine jumped out like yours before I went with an LS engine. It's a fairly common failure point. You can always just replace the regulator (it's really easy on an SI alternator) to see if the problem goes away. I'm guessing SI alternators aren't that expensive these days so it may be worthwhile to replace it before it spikes the voltage for an extended period and starts burning stuff up. If it stays at 16 to 17 volts for very long it will start popping fuses and melting the fusible links.

[another69]

What are my options if I choose to upgrade to a higher amperage alternator? I think the existing one is 65 amps. I have it mounted on passenger side with a simple and effective Summit Racing mount. I have an electric fan now (about 25 amp draw) and plan to add an electric fuel pump in the future, so I may as well upgrade now. I'm thinking something in the 100 amp range would better suit my car. I know there are 12SI units out there that have the same dimensions as the 10SI just with higher output, but I'm wondering if there is something better out there. I was hoping to find something with an internal fan. I will upgrade the charging circuit at the same time. Its fine if I need a different mount, but for now I am keeping the V belt drive.

[GeoffP]

My suggestion is to stick to the SI series alternators unless you want to step up to the larger CS alternators. The CS "mini" alternators can be very unreliable if they are mounted where they don't get good airflow through them. They are also notorious for rear bearing failure. The newer CS series alternator like what comes on the LT1 are more reliable plus they can produce up to about 145 amps if you source it from a police package part number. They are larger and don't have the failure issues from airflow or bearing failure problems that plagued the CS mini. The downside is that you have to use a resistor with the CS alternator to make it charge right. You can't just run a wire to one of the poles on the regulator and have it work correctly like you can with the SI series. GM and some other companies (like MAD) make adapter harnesses for the CS where it can be used in place of an SI. The adapter has the required resistor in it already. As you can tell, I've done a lot with alternators over the years. I've been through the externally regulated to SI conversion a few times, an SI to CS conversion (mini and large) and I've even installed a couple of the new style PCM/ECM controlled units. I hope this info helps you make an educated decision!

[another69]

Yeah, thanks for the info- looks like i'm talking to the right guy! I was looking at getting this:

http://www.summitracing.com/parts/pro-66438

I have not used very many Proform products, and the description (including the one on their website) is very brief. It does seem to be what I am looking for though: internal fan, V belt pulley, 100 amp, internal regulator, 3 wire. It also appears to be a replacement for the 10SI unit that I have now. I assume it bolts in and wires the same as the 10SI. What do you think?

[GeoffP]

Hmm not sure - I'd check Proform's website to see if they provide a wiring diagram. I don't remember who made it but someone use to make an SI alternator upgrade kit that got it right up around 100 amps. Plus it converted it to a 1 wire alt (just the batt pos wire). I'll see what I can find to help you out.

[GeoffP]

http://www.proformparts.com/product-exec/product_id/996/nm/100_NEW_1_WIRE_ALTERNATOR_GM_100_AMP_b_NEW_PRODUCT _b_/category_id/176

Try this one

[another69]

I'm trying to stay away from 1 wire and stay with 3 wire. The original one I was looking at says its 3 wire, but I couldn't find any instructions or literature on Proform's site. It does say on Summit's site that it is a "10SI" body

[another69]

I know that 1 wire is simple, and I like simple, but I read on MAD's website about the pros and cons of 1 wire vs 3 wire, and it seems like 3 wire is the way to go.