Battery Isolators

Submitted: Thursday, Jan 23, 2003 at 14:45
ThreadID: 3068 Views:1738 Replies:7 FollowUps:12
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How can I connect up two batteries in my GU patrol without paying $275.00 (or up to $375) for a Pirahna battery isolator? I cant see the sense in these high price things, there must be some sort of alternative thats cheaper. I currently have a constant rated solenoid between the two which switches out when the key is turned off. I hear that the alternator senses the battery voltage and lowers the charging current when the main battery is full (16.8 volts?)

Help!!!!!!
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Reply By: Truckster - Thursday, Jan 23, 2003 at 14:52

Thursday, Jan 23, 2003 at 14:52
Jaycar is your friend.

head down there and talk to the man.....
AnswerID: 11756

Follow Up By: Bonza - Thursday, Jan 23, 2003 at 14:53

Thursday, Jan 23, 2003 at 14:53
woohoo we have one of them in Melbourne, what do I ask them for?
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Reply By: Peter S - Thursday, Jan 23, 2003 at 15:31

Thursday, Jan 23, 2003 at 15:31
try looking for these www.gsl.com.au or Redarc www.redarc.com.au

Both seem to be getting good reviews from people

You are basically correct in the battery charging.

The other thing to consider is that a link between two batteries will cause a current flow betwween the two if one is discharged and the other fully charged.
This large current flow wil detoriate life of both batteries.

then you have 2 1/2 charged batteries.
AnswerID: 11757

Follow Up By: Phil - Thursday, Jan 23, 2003 at 17:13

Thursday, Jan 23, 2003 at 17:13
Actually, not so.
If the fully charged battery has a voltage of, say, 12.7v at no load, there will be an initial current flow and the voltage of both will rapidly settle at a voltage well above 12v. The current flow is well within safety limits for the batteries. The characteristic of lead acid batteries is that little charging occurs below about 13.0v, so after the initial current there will be not much change in the amount of charge in either, and little current flow.
For example. It takes 45 hours to recharge a 100% discharged battery to 90% charge at a voltage of 13.0v. (from a reference I have) So if the voltage is 12.3v the time would be essentially infinite because the voltage is way below that at which the battery accepts significant charge.

So what you get is an almost fully charged battery and a slightly charged one even though they are connected together. Only a charging voltage above about 13v will equalise the charges because the flat battery will accept current and the full battery little.

As an aside,
When the NRMA jump starts a vehicle with a flat battery using one of those portable battery packs there is no great spark when it is connected.

There are some good references to the characteristics of lead acid batteries on the web and these have been quoted in this forum recentlly Unfortunately I have not got them to hand right now.
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Follow Up By: Oziexplorer - Thursday, Jan 23, 2003 at 19:50

Thursday, Jan 23, 2003 at 19:50
Phil, have you got access to a data logger. If you have, and you hook it up to a Redarc battary isolator and second battery, you will find the modern batteries are quiete different to the older technology batteries. If they were not, I would not be using one in association with my solar panels.

At the end of the day, there is not to my knowledge any battery isolator system that you can buy off the shelf ready to install in a vehicle that is automatic that will adequately charge a second battery in the manner that would be ideal. If there is one, I would love to see and hear about it.
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Reply By: OziExplorer - Thursday, Jan 23, 2003 at 16:24

Thursday, Jan 23, 2003 at 16:24
Bonza as Peter S advised, the Redarc unit is my preferred choice as well.
http://www.redarc.com.au/sbi.htm
These units are available from Ashdowns and most other auto electrical outlets for $110 approx incl GST. Last month they were on special for $85.00 plus GST = $95.00 incl GST.
Suggest you also check out their technical specs here:
http://www.redarc.com.au/sbi-techspec.htm

Redarc also have excellent spike protection, and look at the URL below against what you are presently using. The spikes in modern vehicles can do mighty expensive damage.
http://www.redarc.com.au/sbi-techspec2.htm

The Piranha unit is basically identical to the GSL battery isolator, and believe is made by GSL for Piranha. The GSL has terminals, where the Piranha comes with cables, a flash sticker, anodised red and more than double the price. Personally, I do prefer the Redarc over the GSL unit, but that is a personal preference, not that the GSL is poor. The GSL and Redarc are within two dollars of each other, so price is not an issue.

AnswerID: 11758

Follow Up By: Member - Mike - Thursday, Jan 23, 2003 at 18:01

Thursday, Jan 23, 2003 at 18:01
Ozi, another case of showing my ignorance.
My pre EFI GQ dual battery system has cranking battery connected to deep cycle via 90 amp cable and a simple isolating switch (Pirhana I think - "isolated "red knob is removed). Has worked well for 3 years with same batteries. Overnight plus - I use switch.
Question and advice please - am I living dangerously??!! I have read the REDARC Tech info with interest.
Thanks
Mike
Ps You can see I am not too technically minded!
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Follow Up By: Oziexplorer - Thursday, Jan 23, 2003 at 19:10

Thursday, Jan 23, 2003 at 19:10
Mike, not, not at all. It works, and you don't have all the electronic goodies today that are fitted to petrol and diesel vehicles. What I do like about the Redarc unit, it is fit and forget.

The other reason I like it, you can easily bring in your second battery in an emergency if it is fitted with 1BS but preferably 2BS battery cable and mounted under the bonnet.

Mike the sort of system you have there we used for many years before we got all these lovely electronic goodies to make life easy. Because it is not the latest and greatest, does not mean it is not good or functional.

Mike my philosophy is we are here for a short time, so make it a good time and help others as you would hope to be helped. Life is like agriculture, if you so bad seed, you reap a poor crop.
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Follow Up By: Member - Mike - Thursday, Jan 23, 2003 at 19:31

Thursday, Jan 23, 2003 at 19:31
Ozi, VMT for your reply. I ndo appreciate your responses (crawling here!), but seriously trhanks.
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Follow Up By: Member - Mike - Thursday, Jan 23, 2003 at 19:31

Thursday, Jan 23, 2003 at 19:31
Ozi, VMT for your reply. I ndo appreciate your responses (crawling here!), but seriously trhanks.
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Follow Up By: Member - Mike - Thursday, Jan 23, 2003 at 19:33

Thursday, Jan 23, 2003 at 19:33
Cut off in my prime! David where is spellcheck!
Ozi, glad I live for another day!
Mike
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Follow Up By: Member - Nigel - Thursday, Jan 23, 2003 at 22:32

Thursday, Jan 23, 2003 at 22:32
Mike, your system is actually better than say a manual solenoid system as it won't cause as many problems with surges, etc.

Personally I would forget to switch it on or off and then I wouldn't be happy, so I spent my $$$ for convenience.
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Reply By: brian - Thursday, Jan 23, 2003 at 20:59

Thursday, Jan 23, 2003 at 20:59
I think the question was how to connect two batteries and disconnect one without spending $275,therefore what about connecting the two batteries in parral and adding isolator terminals to the positive post of each battery.i know it is a manual system but is cheap it charges just fine either one or the other or both batteries but relies on your memory,also allows you to isolate both batteries to reduce the risk of theft of the vehicle cost less than $50.


AnswerID: 11768

Reply By: Member - Steven - Thursday, Jan 23, 2003 at 21:59

Thursday, Jan 23, 2003 at 21:59
bonza i have a similar system to you with the solenoid but on top of the solenoid cutting off when you turn off ignition i have a switch under dash to turn it off as well i run a century deep cycle 2nd battery and system works well mine is in a gq cheers steve
AnswerID: 11774

Reply By: Member - Nigel - Thursday, Jan 23, 2003 at 22:42

Thursday, Jan 23, 2003 at 22:42
Bonza you'll still get the problem of parallel charging even with the electronic isolators, unless you get an independent charge type (eg Rotronics RFC12) which can actually remove your starter battery from the circuit as you drive.

This type of system is obviously not as cheap as you'd like so you gotta ask yourself will your use justify the cost? If not stick with what you have or go to a completely manual system as suggested above.

Parallel charging does tend to cause the auxillary battery to be a bit undercharged so they end up only lasting 15-18 months. I personally prefer to get 3-4 years from an expensive battery, so I bought an expensive independent isolator. After 6-8 years I'm better off financially, and I'm young enough to get the long term benefit.
AnswerID: 11782

Follow Up By: Oziexplorer - Thursday, Jan 23, 2003 at 22:47

Thursday, Jan 23, 2003 at 22:47
Reading the Rotronics website, I cannot get excited about them at all.
Having a system that is independent charge and has a diode in the circuit - OUCH! I could not see how you could possibly justify the cost on a Rotronics system. You would be substantially better spending that amount of money on a solar panel if you had a place to mount it full time. I just *love* my solar panels. It is like gold mining, I love it, getting money out of the ground for nothing, solar panels are the same, money from heaven to charge your batteries and run your gear.
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Follow Up By: Member - Nigel - Thursday, Jan 23, 2003 at 23:03

Thursday, Jan 23, 2003 at 23:03
Yep I agree about the solar panel.

The rotronics system doesn't rely on diodes and has the smallest voltage drop of any system, including solenoids. It doesn't charge both batteries simultaneously via diodes, it charges one at a time so the alternator only senses that battery. This allows the alternator to recharge each battery in less time that it takes to charge both together.

All of the vehicles electrical connections (except the starter cable) are removed from the main battery and connected to the switch box.
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FollowupID: 6718

Reply By: Eric - Friday, Jan 24, 2003 at 22:45

Friday, Jan 24, 2003 at 22:45
Bonza.
This problem has been solved a long time ago. The reason both batteries dont charge as well when connected in together is because the wiring loom in your car has resistance in it to limit the current to your battery to 8 amps if 2 batteries are sharing that 8 amps they take a long time to charge, this myth that alternators sence battery voltage is leading you astray, the output voltage of you alternator is constant regardles of battery condition. THe solution to yours and every other dual set up is to disconect you soleniod from you starting battery and connect it to the large terminal on the back of the alternator this will charge you auxilary battery fully and correctly. Eric.
AnswerID: 11831

Follow Up By: Rodeoowner - Sunday, Jan 26, 2003 at 15:13

Sunday, Jan 26, 2003 at 15:13
Eric, I'm interested to hear what you have to say. Can you email me? cullenmarkd@hotmail.com

Cheers.
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FollowupID: 6785

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