Running a 2k at .5 ohms on stock alternator possible?

[MrAcd 10+ year member]

I have found some subs i want and for a good deal problem is he has two and they are dual 2 ohm so i would need to go .5 or 2 ohm. Im on a FSD 2600 and want to run it at .5 since at 2 ohms the subs wont see that much power. This will be a daily beater.

My question is, do you think i should run it on stock alternator, which in my case is a 136 amp alt. I have the big three done and a AGM up front. Think if i get another AGM in the rear i will be good? is there other people who have ran a 2k amp at .5 on there stock electrical? I will give it a go, if you guys think i could do it with the AGM in the front and rear?

Also, what would i need to watch out for, in the case of frying my amp? is low voltage the only thing i need to look out for?

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[wew lad 5,000+ posts]

depends if you're talking about adding a dedicated ground run. i think you'll need a HO alt and 3 batts to be honest, im willing to bet you'll drop into the 11s but using a dedicated 1/0 ofc ground and power run you'll save yourself a good amount of drop

 

[MrAcd 10+ year member]

depends if you're talking about adding a dedicated ground run. i think you'll need a HO alt and 3 batts to be honest, im willing to bet you'll drop into the 11s but using a dedicated 1/0 ofc ground and power run you'll save yourself a good amount of drop

I have "Heard" a lot of others say they done it with only drops into mid 12's and that i would only need 1 or 2 batteries, and others are saying HO and 3+ batteries like you are saying. I will eventually do that but it will be slowly. Could i get away with it at this moment is all. and Dedicated ground run to the rear battery?

 

[wew lad 5,000+ posts]

minimum of two batts and a dedicated 1/0 ofc run from the front batt/alternator for pos/neg

you'll need to be careful with your voltage and watch it very closely especially at idle but you should be ok for a little while

you need to understand that this is a minimum of 250a of current you'll be pulling from the one amp alone

 

[MrAcd 10+ year member]

minimum of two batts and a dedicated 1/0 ofc run from the front batt/alternator for pos/neg
you'll need to be careful with your voltage and watch it very closely especially at idle but you should be ok for a little while

you need to understand that this is a minimum of 250a of current you'll be pulling from the one amp alone

and that is asking for a lot of a stock alternator. I got you. The HO will be an upgrade for sure, but it wont be till at earliest mid summer. and 2 batts total or 2 in the rear?

also will i really gain that much doing a dedicated ground round from the front battery?

 

[wew lad 5,000+ posts]

and that is asking for a lot of a stock alternator. I got you. The HO will be an upgrade for sure, but it wont be till at earliest mid summer. and 2 batts total or 2 in the rear?
also will i really gain that much doing a dedicated ground round from the front battery?

2 batts total if they're decent size, 3 is better. yes a dedicated ground run will make that much of a difference. im only pulling 200a and i get about a volt of drop from a chassis ground

 

[TheFiverMan 10+ year member]

Have a good G34 upfront and a G31 in the rear and you will be fine. Dont let it drop under 12v for long if any.

 

[Papermaker85 5,000+ posts]

adding more batteries gives you more reserve.. have your alt rewound. the use larger windings and higher output diodes. they cost about half a high output on and you can get nearly the same output. fact is the high output alts use the same **** case for most of the midrange output alternators..

 

[TheFiverMan 10+ year member]

adding more batteries gives you more reserve.. have your alt rewound. the use larger windings and higher output diodes. they cost about half a high output on and you can get nearly the same output. fact is the high output alts use the same **** case for most of the midrange output alternators..

Very true maybe he has some one near by that rebuilds Alts But with that size and him being a little smart with his equipment with the added batteries he will be ok.

 

[adulbrich 5,000+ posts]

I wouldn't run that with less than a 270 amp alt.

If you're dead-set on keeping the stock alternator, you can add more batteries, but that won't solve your problem. They won't be able to recharge fast enough with a stock alternator. You'll still have low voltage, but will have more reserve and buffer.

Plus, your stock alternator will go out anyways if you're running that amp at .5 and have bad voltage drop. Stock alternators aren't meant to be putting out their maximum current all the time.

Either way, you'll have to get a new alternator. Basically your just deciding if you want to be hard on your amp or not before you have to buy another alternator.

 

[tymoto21 10+ year member]

watch your voltage at the amp terminals and dont draw it down too low.

you will be fine

i ran my 5k at .5ohm with stock (iirc 90a) alt and 2 old batteries.

as long as you dont crank your gain and try to get every last watt you will be fine.

but do get an alt upgrade sooner rather than later.

also just to play devils advocate, two alt rebuilders local to me wanted more than the other shop who sold me a complete h/o alt. nothing special just higher output.

so shop around

 

[MrAcd 10+ year member]

Well ****, you guys read my freaking mind... I was just locating some local shops that other people here have used to get there alts rewound. I will give this place i found a call tomorrow. It looks like it will be like halve the cost and it might be all i need. I have a Stinger volt meter up front to watch that voltage 24/7. I knew batteries could only go so far since they where reserve and only if i drop below 13v.

Honestly i guess i just need to hook it up and check the voltage and if drops stupid low or something happens i will wire back to 2 ohms and upgrade something else in the electrical. If i can get that alt rewound for a good deal i will do that here soon. Think my FSD 2600 will be okay at .5?

 

[adulbrich 5,000+ posts]

Batteries are reserve, yes, but another member who's no longer active and I have had similar experiences with batteries. Here's what I've found:

When adding batteries, max charging voltage decreases. For example, with one battery in the bank I charged at 15.2v cold and 15.0v hot. With five batteries in the bank I charged at 15.0v cold and 14.7 hot. With 30 batteries, I charge at 14.7v cold and 14.5v hot.

Also, batteries hold what is called a "static charge". From my understanding, it's a bit more voltage than what the battery rests at after being loaded down. "12v" batteries for cars normally rest around 12.6v at a full charge. For those of you with volt meters installed in your vehicle, you may notice that your batteries retain a higher voltage even after you turn your vehicle off. Slowly, the voltage drops to where they normally rest due to internal discharging or the loads on the batteries like a headunit retaining memory.

When adding more batteries, I've experienced something I'd describe as "capacitance" above the resting voltage. Batteries have a little extra power to give to amps above what they normally rest at. I've heard people say "adding batteries only helps you maintain power at battery voltage". This is implying that batteries are only really supplying current to meet demand when voltage drops somewhere below 13v. I disagree with this. I think batteries can help maintain a higher voltage.

Working at a battery shop, I charge and load test batteries on a daily basis. I've learned a lot. Normally if a battery comes in and the person says" they had to jump it to get it here, it's been having trouble starting, blah blah blah" (typical story) I load test the battery and if it load tests bad we replace it. At the shop, we have a warranty of one year for free replacement. Also, there is a "5 year prorated warranty" where we'll offer a discount on a replacement if it goes bad after the first year. Sometimes, a bad battery can briefly test good after a vehicle has charged it and just been turned off. After knocking the "static charge" off, you can take a better look at the condition of the battery. Also, after putting a trash battery on a charger and pumping it with 200 amps of current, you can make it temporarily hold a high voltage and even load test decently one time.

The more batteries I add, even with more current demand, I find that maximum system voltage is lower, but I also have less drop. Lowest I've seen so far with the new bank is 13.9v. That's with three 7k's wired to .35 nominal. With the TFE wired at .5, the same alternators, and just five batteries, I was in the low 13's going full tilt and had previously dipped into the high 12's. Nobody can tell me that the batteries weren't helping maintain that higher voltage. I've got the same alternator power, but more current demand and am having less voltage drop.

Just my two cents on electrical theory stuff

EDIT: I'm going to make a new thread about the subject, because I'd like to talk about it more and see what other people have to say

 

[wew lad 5,000+ posts]

sounds like adulbrich is learning, glad to see that.

 

[adulbrich 5,000+ posts]

Thanks, lol.

Besides the obvious benefit of earning money, working at the battery shop has given me lots of good experience and knowledge.

Also, I get quite a bit of free stuff, haha. I've got a ton of jumper cables that were going to be just thrown away, some transformers, circuit breakers, plugs, miscellaneous parts, and some small free button cell batteries. Can also borrow tools like the hammer crimper and heavy duty battery charger so I don't have tom buy them!