voltage drop when load is applied with HO alternator

[Miguels]

if youre checking on the lighter most likely its not accurate.. i have a voltage meter on my epicenter and with nothing on on i see 14.01 and 13.8.. once i turn lights on i see it drop to 12.9.. i go with my dmm and check and the alt is maintaining 14v

have someone mess with the windows while you check alt with a dmm.. also having a big alt dont mean you will not see voltage drop.. you will see a small drop before the alts kicks in.. the drain is fast for the alt to keep up.. thats why you see it drop a little with the bass notes.. battery bank will help in this situation but will always see a small drop before the alt produces the amperage to keep the voltage at 14v

[LoudBimmer]

I'm thinking about adding PCM and increasing charging voltage to 14.8V.

Also looking at getting a bigger amp (~2000watts) and seeing what will happen with bigger load.

Other thing I will try to do is swapping batteries. Maybe my D3100 went bad, who knows.

[rickybobby]

I'm thinking about adding PCM and increasing charging voltage to 14.8V.

Also looking at getting a bigger amp (~2000watts) and seeing what will happen with bigger load.

Other thing I will try to do is swapping batteries. Maybe my D3100 went bad, who knows.

wait what? look up these parts that everyone is talking about. adding a PCM is not possible..... i dont think your d3100 went bad. we need to see

pictures of your install on your batteries and big 3. it will help alot

[rickybobby]

Well, I'm trying again to fix this issue. car BMW e46 325i

So right now I have 260amp alternator with a xs power D3100 battery(fully charged). I also replaced belt and tensioner pulley. At 2k rpm voltage stays at 14V (normal for my car.)

When ever I apply a small load, like rolling windows up, my voltage would dip down to 13.7 for a second and back to 14v. If I turn the heater on, headlights and fog lights, voltage goes down to 13.4-13.6. even if I keep my rpms@2k. WHY?

If I understand it correctly, at 2k rpm alternator puts out 260amp, so a minor load should not cause a voltage drop. It doesn't look like a belt slip, since the voltage stays constant while I drive. Only when load is applied it does this.

I tried using different alternator (stock) and it was doing the same exact thing. So does this mean I have a bad relay somewhere? or wtf is the problem?

I had HO alternator tested and it was 100% functional. I was told that I need to get a better belt wrap to fix this issue. But seeing how even the stock was doing this, belt wrap is not an issue.

What else can it be?

this is normal.

[LoudBimmer]

I'm thinking about adding PCM and increasing charging voltage to 14.8V.

Also looking at getting a bigger amp (~2000watts) and seeing what will happen with bigger load.

Other thing I will try to do is swapping batteries. Maybe my D3100 went bad, who knows.

wait what? look up these parts that everyone is talking about. adding a PCM is not possible..... i dont think your d3100 went bad. we need to see

pictures of your install on your batteries and big 3. it will help alot

I meant to say external regulator. Don't know why I said PCM. lol

I don't have big 3, since my alternator only has a positive terminal. But I have a 0 gauge run from alternator positive to battery positive. and 0 gauge from battery negative to the frame.

[rickybobby]

It would make sense to see a quick voltage drop due to the stock electrical being small ( 16gauge wire).

I will re-check voltage at alternator and in the back where battery is with 0gauge wire run.

One other thing, so does alternator put out 260A@2k rpms? Constant 260A to the battery or only when it requires the 260A??

The draw has to be there for the output to be supplied. With everything off, there's infinite resistance and nothing to pull current. At 2k RPM, the current should be available but just needs something to draw it.

[LoudBimmer]

It would make sense to see a quick voltage drop due to the stock electrical being small ( 16gauge wire).

I will re-check voltage at alternator and in the back where battery is with 0gauge wire run.

One other thing, so does alternator put out 260A@2k rpms? Constant 260A to the battery or only when it requires the 260A??

The draw has to be there for the output to be supplied. With everything off, there's infinite resistance and nothing to pull current. At 2k RPM, the current should be available but just needs something to draw it.

I will do more testing this weekend. Gonna try different battery. test the voltage at alt output, back pretty much everywhere.

[rickybobby]

ok sounds good. when you are testing the voltage, Do this- 1.hook your amp up in the trunk to the back battery hook a sub up to the amp, 2. turn the radio up ,3. play music, 4. hook up your meter to the back battery, 5. turn amp gain up a quarter turn while watching your volt meter/DMM to see what your voltage does. with the engine running at idle. then let us know what happened.

[OrzechNJ]

mine singer alt was doing the same thing.. on cold, voltage was about 14.5-6 then went down to about 14.0-1.. voltage was going down when i rolled windows down, turned hids on etc.. however it was going back on 14 right away and i had no voltage drop with about 1800rms and d3400 under the hood...