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Old 01-11-2017, 03:04 PM   #1
defeo94

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What is the purpose of a car isolator?

I have dual Sundown SA8's powered by a Hifonics Brutus 1316D connected to 2ohms pushing 900 RMS. Stock 85A alternator, but a powerful Odyssey battery under the hood.
I tend to lose a lot of voltage after running the system for a period of time (like, 30 minutes of loud blasting)
Spoke with a car audio expert in a local shop and he told me I need a second battery installed with an isolator. He said a HO alternator isn't necessary for just 900 RMS.
This system is in my 2003 Mitsubishi Galant.
Thank you,
DeFeo94
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Old 01-11-2017, 04:37 PM   #2
basicxj

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Quote:
Originally Posted by defeo94 View Post
I have dual Sundown SA8's powered by a Hifonics Brutus 1316D connected to 2ohms pushing 900 RMS. Stock 85A alternator, but a powerful Odyssey battery under the hood.
I tend to lose a lot of voltage after running the system for a period of time (like, 30 minutes of loud blasting)
Spoke with a car audio expert in a local shop and he told me I need a second battery installed with an isolator. He said a HO alternator isn't necessary for just 900 RMS.
This system is in my 2003 Mitsubishi Galant.
Thank you,
DeFeo94
An isolator is installed to prevent an additional battery for the audio system from discharging your starting battery under the hood. If you connect both batteries to the same points in the vehicle, if one gets discharged it will try to equalize its state of charge with the other battery. The isolator is installed in the circuit to allow charging to happen for both batteries but prevent one from discharging the other.

Hint: Many "experts" at car audio shops will be more than happy to feed you a line in order to sell you something (products, services), whether that something helps your problem or not. In your case, a second battery will not help the issues you are experiencing. An additional battery will extend the length of time you can play the system with the engine off, but will not provide more current- that is limited by your vehicle's alternator (which is too small for the task at hand). If your alternator is already too small for the amount of draw you are putting on it, asking it to charge a second battery will tax it further.
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Old 01-12-2017, 12:48 PM   #3
SPL_Krayzie112

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Switch over to Optimas...
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Old 01-12-2017, 02:31 PM   #4
ckeeler11

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+2 on what Basic said. You have a tiny alternator that is where the problem is located.
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Old 01-12-2017, 07:29 PM   #5
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A HO alt isn't needed for 900wrms. However, you can have your stock alt rebuilt/rewound to 125-135A easily for around $60. Fixes your problem. No need for 2nd battery & iso which would cost $120-160.
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Old 01-12-2017, 08:10 PM   #6
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Quote:
Originally Posted by neillio View Post
A HO alt isn't needed for 900wrms. However, you can have your stock alt rebuilt/rewound to 125-135A easily for around $60. Fixes your problem. No need for 2nd battery & iso which would cost $120-160.
He has one of these on a stock 85A alternator and has been experiencing dimming, battery and alternator failure:

http://www.sonicelectronix.com/item_...RX1516.1D.html

I suggested he get the rewound alternator for more output here (in post #11):

http://www.caraudioforum.com/showthread.php?t=383452

...but he stated he was against it and wanted to add a second battery. It was explained that would not solve the problem.
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Old 01-12-2017, 10:10 PM   #7
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I was surprised that using a 1200 watt amp on my stock Honda never dimmed the lights but I use a much more reasonable 450 watt total system power now.
However I did own a car once with dimming issues when the bass hit and a capacitor did prevent it from dimming but my batteries were shot within a year or so and likely was killing my alternator too but ditched the car before that happened. Always wise for better alternators and I think they make brackets so you can install more than 1 alt if there's room.
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Old 01-12-2017, 11:30 PM   #8
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If he's going to sell the vehicle is a few months, it makes sense to have the current alt rewound to around 125A. If the car is experiencing charging system issues, you can remove your stock alt in 15min and take it to a starter/alternator shop. If even slightly unsure on how to do it, youtube will show you. Will you need to borrow a vehicle, or get a rental for 2-3 days? Possibly.
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Old 01-18-2017, 06:04 PM   #9
Coryf

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900 watts divided by 14.4 volts is 62.5 amps. plus all your other electronics the alternator is powering... yeah you prob need a bigger one.
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