battery

Submitted: Monday, Sep 26, 2016 at 17:16
ThreadID: 133504 Views:3858 Replies:14 FollowUps:10
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how to stop the current flowing back to my anderson plug from my caravan battery
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Reply By: Member - mechpete - Monday, Sep 26, 2016 at 17:26

Monday, Sep 26, 2016 at 17:26
So whats the problem with that
Mechpete
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Reply By: skulldug - Monday, Sep 26, 2016 at 17:40

Monday, Sep 26, 2016 at 17:40
unplugging it should work
AnswerID: 604668

Reply By: Member - Roachie - Monday, Sep 26, 2016 at 17:46

Monday, Sep 26, 2016 at 17:46
Install a DC-DC charger on board the caravan, fed via the Anderson plug.

No current will flow back to the Anderson plug from the caravan battery/ies AND you will (should) get a better state of charge too.
AnswerID: 604669

Follow Up By: gbc - Tuesday, Sep 27, 2016 at 20:02

Tuesday, Sep 27, 2016 at 20:02
Actually some dc chargers will reopen the alt feed side once the van batteries are charged and back charge the tug batteries as well (assuming there is solar or other 12v on the van supplying excess power). The ctec 250 does this.
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Follow Up By: Member - Bigfish - Wednesday, Sep 28, 2016 at 13:31

Wednesday, Sep 28, 2016 at 13:31
Get a dcdc charger that is IGNITION fed...problem solved.
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Follow Up By: gbc - Wednesday, Sep 28, 2016 at 19:26

Wednesday, Sep 28, 2016 at 19:26
I'm not sure that will fix it.
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Reply By: Allan B (Member, SunCoast) - Monday, Sep 26, 2016 at 18:09

Monday, Sep 26, 2016 at 18:09
How is your vehicle Anderson plug supplied from the vehicle's crank-battery/alternator? Is there an isolator solenoid etc.?
Is anything else such as a vehicle fridge connected to that line?

If there IS an isolator and no other loads on the line from the crank-battery to the Anderson then there would be no problem with the caravan battery being connected as there would be no current back-flow.
Cheers
Allan

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Reply By: scruffy - Monday, Sep 26, 2016 at 18:52

Monday, Sep 26, 2016 at 18:52
Why would it matter. Mine does the same. Havent had a problem with it in 2 years.
AnswerID: 604673

Reply By: Robin Miller - Monday, Sep 26, 2016 at 19:02

Monday, Sep 26, 2016 at 19:02
I just put a diode in the power in wire from the car.
(actually I have 3 schottky 7amp diodes in parallel which minimizes voltage drop to a small 22ah battery)

Now while thats easy to say we have no idea of your Vans battery size.

If you have big van battery and its nearly flat you could draw a lot of current while it chargers.

But its very cheap to play around.

get a ZR-1324 diode bridge from jaycar about 5 bucks .

These are 4 diodes in a bridge but you only connect up 2 leads.
The reason I suggest these is because they have a mounting hole.
(also if you juice a diode, well theres spares in the bridge.

Imperative to include an inline fuse (20 amp).

You can be tricky and optimize the above further , but I have been told I get into to much engineering detail , so I'll leave it there for now.





Robin Miller

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Follow Up By: The Bantam - Tuesday, Sep 27, 2016 at 08:35

Tuesday, Sep 27, 2016 at 08:35
But now you have reduced your caravan charging voltage by 0.6 Volts.

Most caravans have problems with charging efficiency already, because of the voltage drop in the cables. Dropping another 0.6 volts is unhelpfull.

Peopl are looking at boosing their alternator voltage these days, because of poor charging efficiency.

Diode Isolators where a thing in the past ... Jaycar did at one time stock them.

But you can Buy a basic relay isolator for about $60 ...... and most of them are good for 100 amps.

Cheers
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Follow Up By: Member - Boobook - Tuesday, Sep 27, 2016 at 15:01

Tuesday, Sep 27, 2016 at 15:01
Yeah there is enough voltage drop in most caravan charging situations, let alone having a diode in series, even a Schottky one. That could be a volt or more.

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Follow Up By: Robin Miller - Tuesday, Sep 27, 2016 at 15:50

Tuesday, Sep 27, 2016 at 15:50
Yeah , no it doesn't work that way guys.

Schottky diodes are only approx. 0.3 v .

In practise diodes don't actually cut right off anyway and will trickle charge lower drops.

My battery for example usually sits at about 0.2v and the simplicity of the solution , lack of constant relay current draw and extra wiring means it has a place - but its not for all situations.

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Follow Up By: Member - Boobook - Tuesday, Sep 27, 2016 at 16:07

Tuesday, Sep 27, 2016 at 16:07
It is hard ( expensive) to get a Schottky diode with more than about 10 - 20A capacity. And a Schottky at, or near its rated current will have a voltage drop of around 0.4 to 0.5V.

To get a voltage drop of 0.2A, the current usually has to be in the milliamps from my research in the past.

Which Schottky diode are you using that can handle charging currents and only has a drop of 0.2V Robin? That would be of interest to a project I have been working on for some time. Also are you aware that the bridge you refer to is a standard silicon bridge, at 40A it has a voltage drop of about 0.8V
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Follow Up By: Robin Miller - Tuesday, Sep 27, 2016 at 17:20

Tuesday, Sep 27, 2016 at 17:20
Hi Boobook

That's the trick , you don't need to run the device(s) at its peak.

In my top reply here I referred to using 3 cheapies in parallel which maximizes the performance and was appropriate for my case.

The 0.2v drop only occurs at very low currents hence my reference to "Trickle charging". (sort of free top up that keeps battery fresh)

Also at the other end , it doesn't matter much that if you are drawing heavy currents and voltage drop goes up when the battery is low because in this mode
the battery has a lower terminal voltage anyway.

That's the beauty of this simple system, apart from preventing the backfeed issue - its also self regulating , as battery demand drops off and its terminal volts increase then the need for charging current decreases.

You will find the same principle used in solar panels.









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Reply By: Member - Charlie M (SA) - Tuesday, Sep 27, 2016 at 09:47

Tuesday, Sep 27, 2016 at 09:47
I just have another Redarc auto solinoid in the caravan, It activates when car running, stops when voltage back to about 12.5 volts.
Cheers
Charlie
AnswerID: 604682

Reply By: Paul and Mel - Tuesday, Sep 27, 2016 at 16:38

Tuesday, Sep 27, 2016 at 16:38
I have a simple solenoid on mine connected to the 7 pin plug for control from the vehicles ignition. Ignition on=solenoid on and charging van battery. Ignition off=solenoid off batteries isolated and no power on anderson plug on van... Simples.
AnswerID: 604694

Reply By: KiwiAngler - Thursday, Sep 29, 2016 at 14:27

Thursday, Sep 29, 2016 at 14:27
In my travels last year I ended up in a shop that had the biggest range of Anderson fittings I have ever seen (unfortunately can't recall which town)
One of which had a diode fitted onside it to (according to sales guy) prevent the current flowing back the other way
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Follow Up By: Nomadic Navara - Saturday, Oct 01, 2016 at 09:33

Saturday, Oct 01, 2016 at 09:33
I bet he did not tell you about the voltage drop that the diode causes.
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Reply By: Member - Rod N (QLD) - Thursday, Sep 29, 2016 at 17:02

Thursday, Sep 29, 2016 at 17:02
Current will only flow if one voltage is higher than the other.
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Reply By: Batt's - Friday, Sep 30, 2016 at 13:55

Friday, Sep 30, 2016 at 13:55
A simple on/off switch tapped into the positive wire that's in an easy to get at place. Just have to remember to turn it back on when traveling not so bad if you forget and have enough solar panels to put charge into the battery or batteries.

I had a switch set up in my 4WD yrs ago which isolated the anderson plug on the back of the vehicle forgot to turn it on and wrecked the van battery. I think fitting the rubber end caps to the anderson plugs is an easier option and less expensive than replacing a battery.
AnswerID: 604774

Reply By: Allan B (Member, SunCoast) - Friday, Sep 30, 2016 at 14:04

Friday, Sep 30, 2016 at 14:04
.
A heap of conjecture here but still "kjsisscar" has not returned to clarify what his problem and actual setup are!

Seems that some of us do not even need an understanding of the issue in order to solve it. LOL
Cheers
Allan

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Reply By: kjsisscar - Friday, Sep 30, 2016 at 15:09

Friday, Sep 30, 2016 at 15:09
Hi kjsisscar here i thank you all for your help. I think putting a switch as one of the members noted would be the best idea for me ,i just did not want the anderson plug from the caravan left live when disconnected from the tow vehicle.thank you.
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Follow Up By: TomH - Friday, Sep 30, 2016 at 15:47

Friday, Sep 30, 2016 at 15:47
Why???????
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Reply By: Maggsie - Saturday, Oct 01, 2016 at 12:15

Saturday, Oct 01, 2016 at 12:15
I second that. Why? The Anderson and trailer plugs on your vehicle are still live after disconnection, unless you have some way of isolating them.
Maggsie

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