70 AMP BATTERY ISOLATOR

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70 AMP BATTERY ISOLATOR

Postby Gary T » Tue Jun 20, 2006 5:13 pm

Has anyone used somthing like this.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93801

Does this take the place of a seperate charging circuit run to the alternator?
Gary T.

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Postby PaulC » Tue Jun 20, 2006 5:40 pm

Hi Gary, I've used battery isolators on both of my trucks for dual battery set up. If you are thinking of using this for your trailer battery you will need to run full size battery cable thru to the trailer, probably via an Andersen plug. I used to have a trailer with a battery that was charged via the alternator, through the trailer plug with 6mm(?awg) cable and an isolating relay to stop discharge of the car battery. Probably the easiest way to keep the trailer battery topped up. I'm not going into the deep cycle v normal crap here, just a basic idea I used and it worked.
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Postby Chuck Craven » Tue Jun 20, 2006 6:51 pm

Yes I have used them! They are used on mini motor homes and such. Both batteries will charge up to near full charge. The alternator goes to the center lug and each batter goes to the side lugs. That is what I will be using on my tear. Both batteries need to be approximately the same size amp hour ratted. One is your start battery and one a deep cycle battery for camping. My plan is to have dual battery in the car and use an Andersen plug to disconnect the one in the car and connect the battery in the tear to charge it when traveling. If the tears battery runs down when dry camping I will just swap batteries with the one in the car. And recharge it when running around sight seeing. :)

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Postby GeorgeTelford » Tue Jun 20, 2006 7:48 pm

Hi

Yes they work, requires you to remember to switch back and forth.

I have got to disagree with Chuck, batteries will get NOWHERE near a full charge from a standard vehicle alternator, it will never get a battery much beyond 70 % Most experts now agree that 65% is more realistic.

If you are going to charge the battery with a decent staged charger then the switch is a good idea, it means you wont discharge the battery that you have filled at home, while traveling out to the campground, but it gives you the option for when you are out and about and want to add a little back via alternator.

Paul, If you are using an Isolating relay, what is the point of having the switch too?

FYI 6mm is 9 AWG
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Postby PaulC » Wed Jun 21, 2006 1:09 am

George, What switch are you talking about? Unless I'm missing something here I have'nt seen a switch required anywhere. That isolator does'nt have a switch on it so what do you mean by "having to remember to switch back and forth"?
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Postby madjack » Wed Jun 21, 2006 1:14 am

Paul, some isolators have a switching mechanism to allow one, both or none of the batteries to be put into play...some are just large diodes that allow current to flow in one direction only(probably what you have)...
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Postby PaulC » Wed Jun 21, 2006 1:40 am

Hi MJ, Understand all that. I was just a little confused when George suggested that you had to switch the electronic isolator that Gary shows in his link. Both of the isolators I have are very similar in operation to the one shown. Some of my friends have the manual switch that you describe.
I don't profess to know how they work but I've been told they operate on voltage balance versus the main battery being at optimum charge at all times.
The relay I had on my old unit was so that the battery only received charge when the vehicle was running. When the motor was turned off it isolated the trailer battery from the car circuit.
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Postby madjack » Wed Jun 21, 2006 1:45 am

..believe me when I say the actual electronics are a mystery to me also...all I know I have seen switched and unswitched ones.
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p.s....my bad, I guess I should've looked at the link...that unit is automatically switched internally....there is no manual switch...
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Postby GeorgeTelford » Wed Jun 21, 2006 3:54 am

Hi Paul

My bad, Like Jack I read the original post to mean a manual Isolating switch, when I read your post, it seemed to mean that you would have a switch as well as the isolating diode.

Quote Paul C I don't profess to know how they work but I've been told they operate on voltage balance versus the main battery being at optimum charge at all times.

Just to clear this up, your sources are incorrect, the Isolator is a diode, basically there are 2 one way streets leading away from the middle pin, Optimum charge, hmm there is the biggey

There is an experiment I have always wanted to do to see if an Isolating diode, improve's the charging beyond 65-70 %

The reason that a battery doesnt get fully charged via an alternator are very complex ( to the point that when I have demonstrated this to some people with degree's in electronic engineering and they still cannot get their head round whats happening )

Anyway onwards, the diode has 2 known effects, one it keeps the batteries totally isolated from each other, this is because diodes only allow power one way, the other is that they use up approx .8 Volt doing it and there is the rub. for comparison isolating relays allow the batteries to see each other when the alternator is running.

An alterntor puts out 14.4 to 13.8 Volts, with an isolating diode inline, this instantly drops to 13.6 to 13.0 Volts and thats before any voltage drop due to wiring.

To summarise

1. They are the surest means of battery seperation
2. There are no "backfeed" losses beacause of the above
3. There is a voltage drop penalty
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Postby GeorgeTelford » Wed Jun 21, 2006 3:57 am

Hi again

Here is my Isolating diode and some information on diode splitting

http://www.sterling-power.com/htm/di.htm
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Postby PaulC » Wed Jun 21, 2006 6:42 am

George, KISS- I don't need to know! I use the Henry Ford principle in cases like this :lol:

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Postby GeorgeTelford » Wed Jun 21, 2006 7:26 am

Hi Paul

I don't need to know! I use the Henry Ford principle in cases like this


So you dont know? so why make statements about something you do not understand? you said "Probably the easiest way to keep the trailer battery topped up", I think to most people that implies a constantly full battery.

If you were to measure the voltage from the Alternator and then measure the voltage that actually reachs the teardrop battery, you will see a big drop (over 1 Volt lower)

Now given that a standard alternator cannot fully charge a single battery when all the charge is applied direct only 2 to 3 feet away, how can that same output (fully) charge a second battery that is many feet away having lost around .8 Volt minimum just via the isolating diode and more via the long length of wire to the second battery.

Nothing at all wrong with keeping it simple, as long as simple works well.
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Postby dacrazyrn » Wed Jun 21, 2006 10:22 am

So this basically works as a switch. I read through the manual and it's application is for the engine compartment.
Couldn't this just as easily be put into THE TEAR and the "power" coming from the 12V trailer plug be routed through prior to going to the battery? Basically keeping THE TEAR and vehicle battery seperate?
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Postby madjack » Wed Jun 21, 2006 10:38 am

...I read the manual also and here is my problem...I know that you can run a 10ga wire from the alternator to the camper battery(did it for years onna 22'er I had). I had no isolator but simply unhooked the wire when stopped so...why do I want to use somehing that requires that I run a full sized battery cable all the way to the camper...isn't there some kind of isolator that I can put in the camper and just run that same 10 ga wire??? I don't want the expense of a full sized battery cable(20/30'worth) and its attendant routing problems...there has to be a simpler way such as I did on my old 22'camper...
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Postby dacrazyrn » Wed Jun 21, 2006 10:41 am

same thing I am asking, basically...you could still wire your 10ga to it....I would think.
Or is there a better solution (that doesnt cost me my next born).
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