Adding a second battery
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Elder User
Joined: Apr 2006
Posts: 850
Likes: 3
From: West Granby, CT.
Adding a second battery
I've done some research and decided to go with an isolator and second battery. The second battery is mainly for the plow as it draws so much juice it isn't funny. I am mounting the battery on the frame rail on the passengers side in a plastic battery box. I will run 1 gauge to the isolator & 1 gauge to a ground on the motor.
2 questions - What's the general opinion of doing this? good? bad idea?
Does any one know the exact size of my alternator? I can get a 120 or 160amp isolator and would prefer the smaller size for mounting purposes. I have an 08 5.4.
Thank you for your input.
2 questions - What's the general opinion of doing this? good? bad idea?
Does any one know the exact size of my alternator? I can get a 120 or 160amp isolator and would prefer the smaller size for mounting purposes. I have an 08 5.4.
Thank you for your input.
Postmaster
Joined: Apr 2006
Posts: 3,524
Likes: 2
From: CA Bay Area
I had several bad experiences with insulators on my motorhomes. Not only they drop the voltage, but couple of them had leaks and drained batteries.
Way better is battery combiner, or in your case simple relay activated by ignition should work. Those 200 amp continuous duty relays are hard to buy, but last time I combined several 70 amp relays that sold very cheap on ebay.
Way better is battery combiner, or in your case simple relay activated by ignition should work. Those 200 amp continuous duty relays are hard to buy, but last time I combined several 70 amp relays that sold very cheap on ebay.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
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From: Long Island USA
Get an isolator that's rated at least twice the max amperage of your alternator. That way it's not stressed too much, the voltage drop won't be as bad.
Overheating the thing will cause it to short out the rectifier. So mount it somewhere it can get air flow, the engine compartment might NOT be the best thing for it especially when you're plowing.
A starter solenoid makes a good high-amperage switch if you don't go with an isolator.
Overheating the thing will cause it to short out the rectifier. So mount it somewhere it can get air flow, the engine compartment might NOT be the best thing for it especially when you're plowing.
A starter solenoid makes a good high-amperage switch if you don't go with an isolator.
Cargo Master
Joined: Dec 2007
Posts: 2,196
Likes: 120
From: Carstairs Alberta
the only time you need an isolator is if you are planning to operate your electrical load extensively while the engine is not running. now unless you have figured out a way to plow snow without the engine running, that really should not be an issue for you. Save the money and aggravation and just hook the second battery up direct
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Elder User
Joined: Apr 2006
Posts: 850
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From: West Granby, CT.
the only time you need an isolator is if you are planning to operate your electrical load extensively while the engine is not running. now unless you have figured out a way to plow snow without the engine running, that really should not be an issue for you. Save the money and aggravation and just hook the second battery up direct
Postmaster
Joined: Jun 2008
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From: Wayyy NoCal, USA
The starter wouldn't care if you had 1 or 200 batteries. It's going to draw as much current as it needs from whatever source you give it.
Postmaster
Joined: Apr 2006
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From: CA Bay Area
There is big difference between dual batteries and dual battery banks.
Having dual batteries is common on diesels and with basic know-how it is no big deal.
Dual battery banks are used when second bank is being discharged with engine off and you want preserve starting power in the first bank.
That applies to motorhomes and Police cruisers that use lot of lights with engines off.
I am not familiar with snow plow, but as nitrogen indicate, not likely you really need it.
Having dual batteries is common on diesels and with basic know-how it is no big deal.
Dual battery banks are used when second bank is being discharged with engine off and you want preserve starting power in the first bank.
That applies to motorhomes and Police cruisers that use lot of lights with engines off.
I am not familiar with snow plow, but as nitrogen indicate, not likely you really need it.
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Mountain Pass
Joined: Oct 2007
Posts: 185
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I haven't heard that one before! Just hook them together in parallel - positive to positive and ground the negative. Nothing bad will happen.
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Thread Starter
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Elder User
Joined: Apr 2006
Posts: 850
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From: West Granby, CT.
Some research I found on the isolator says it would "charge" both batteries equally and seperate accessories (my case plow) from the truck battery?
My whole reason for doing this is to prevent the lights/defroster from dimming everytime I use the plow. I can't believe it is good for the truck to draw so much current over & over & over and having motors and lights dimming.
Mountain Pass
Joined: Oct 2007
Posts: 185
Likes: 1
As Nitrogen said, isolators are typically used for running things from a second battery when the engine is off. You can run that battery down and still start your engine with the other battery. When the engine is running both batteries are connected together and the plow would be pulling current from both anyway. So I see no need for an isolator or relay. The lights are dimming because the plow is pulling a huge current load from the battery. With two batteries in parallel, you have twice the capacity to pull current from so the battery voltage shouldn't dip as much and you'll see less light dimming. It may not go completely away but should be improved. Make sure the plow is connected as close to the battery post as possible - preferably at the post.
Cargo Master
Joined: Dec 2007
Posts: 2,196
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From: Carstairs Alberta
yup sebs and mw are dead on. pos to pos =2x the amperage available, same volts. even perfect connections have a voltage drop, so the more connections between the battery and the alternator the lower your voltage at the battery. wiring in an isolator just adds another level of connections. they will charge better and more equally without an isolator in my opinion.
Mountain Pass
Joined: Feb 2005
Posts: 162
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From: Hudson, NH
For what it is worth I agree with the above. I am not familiar with 'isolators' used in vehicles but my assumption would be that they are nothing more than a big diode (or bank of diodes). As soon as you throw a diode in you are going to lose .7Volts from the natural forward voltage drop of a diode.
I would also strongly suggest you ensure that both batteries, the existing and the new, are of a similar age. If the existing one is more than 1-2 years old I would replace it at the same time. Otherwise the newer battery will be pulled down to the older one and spend a bunch of its time trying to charge it.
This is a common problems for battery banks on big UPS systems and Solar systems so I thought I would mention it.
---Aaron
I would also strongly suggest you ensure that both batteries, the existing and the new, are of a similar age. If the existing one is more than 1-2 years old I would replace it at the same time. Otherwise the newer battery will be pulled down to the older one and spend a bunch of its time trying to charge it.
This is a common problems for battery banks on big UPS systems and Solar systems so I thought I would mention it.
---Aaron
Posting Guru
Joined: Jan 2010
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From: Whitecourt AB, Canada
Even more important on 48-52V systems because most of those banks are made out of 2V single cells and in a big series string instead of multi-cell batteries in parallel... one open or shorted cell messes everything else up.
FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
One problem is when you use that plow a lot, you WILL drain both batteries if the alternator isn't big enough to keep up with it.
If you're going to just wire in another battery, get a real voltage gauge and keep an eye on it. You could potentially shut down the truck and not get it started again
If you're going to just wire in another battery, get a real voltage gauge and keep an eye on it. You could potentially shut down the truck and not get it started again