Nissan Navara d40 2006 dual battery

Submitted: Saturday, May 04, 2019 at 13:12
ThreadID: 138274 Views:1551 Replies:6 FollowUps:15
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hi all, i am confused, i have a brand new AGM battery fitted on the back with idc25 dc to dc charger at the back, with 5 meters 8 B&S red from starting battery positive to input of charger and a black from starting negative to charger and aux negative, another 8B&S from output of charger to aux positive, when the car is running and the aux battery is around 12V, the main battery shows 14.4V and when the charger sense the voltage it starts to charge, but as soon as it starts to charge the voltage at the charger input cable drops to 12.2 to 12.5, thus stops charging and the voltage rises again to 14.4, and this process repeats, does this mean the smart alternator kicks in? now the confusion is here, while the voltage keeps changing from 14.4 to 12.2 at the charger input cable the other end of the same cable at the main battery stays constant at 14.4. so is this normal? and if i connect the ignition cable of the charger to ign, would that fix this very slow charge process? any advice is appreciated
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Reply By: Frank P (NSW) - Saturday, May 04, 2019 at 14:45

Saturday, May 04, 2019 at 14:45
The constant 14.4 at the starting battery suggests to me that the alternator/charging system is not of the low voltage "smart" variety.

If you have 5m of cable from crank +ve to the charger and another 5m between the negatives, that's a 10m circuit. 25amp output may be calling for about 30 amp input.

8 B&S for a 10m 30 amp circuit is a bit light on, IMO. 6 B&S might be more appropriate.

Before you spend $$ on re-cabling, I'd try a couple of things:

- Check and re-check EVERY connection, crimp and terminal to ensure a good electrical connection, including fuses/circuit breakers if have them (you should).

- Try taking the charger neg and the aux battery neg with short 8 B&S or heavier cables to good chassis earths. If your charger is near the aux battery (your post suggests it is, which is good) you could run charger neg to aux battery neg to nearby chassis earth. That cuts out nearly 5m of your cabling which may improve things.

AnswerID: 625358

Follow Up By: Allan B (Sunshine Coast) - Saturday, May 04, 2019 at 16:05

Saturday, May 04, 2019 at 16:05
.
I agree with what Frank says, especially that the 8 B&S cable is a bit light on.
But even that size cable should not be producing the reported 2 volt drop.
Are you absolutely certain that you have 8 B&S?

As to the question of connecting an IGN signal to the charger blue wire.....
I am unsure if your vehicle has a "smart alternator" however it may overcome your problem. Your charger currently has a turn-on voltage of 13.4v and a turn-off of 12.8v. With the IGN connected to the charger blue wire the turn-on is 12.2v and the turn-off is 11.9v.
However that 2.0 volt drop on your cable is confusing the charger and really needs to be addressed.
Cheers
Allan

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Follow Up By: RMD - Saturday, May 04, 2019 at 16:23

Saturday, May 04, 2019 at 16:23
Same as Frank and Allan.
You can use a multimeter set on volts and length of wire to connect the multimeter between the main +terminal and the Chargers input + terminal. That will verify any voltage drop in the positive supply line, should be less than 0.5 v if possible and the negative line can be checked in the same way. As Frank mentioned, the voltage drop, VD, no one wants it, is happening in both lines so the additive effect if present may be causing the issue.

Although many don't like it I use the chassis, like Frank said is an option, and an additional heavy cable from the chassis to the main battery negative and so the charger negative is also a heavy cable to the chassis. From the main to charger there is a very heavy orange welding size cable and using this method sees not much voltage drop at all.
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Follow Up By: HKB Electronics - Saturday, May 04, 2019 at 17:37

Saturday, May 04, 2019 at 17:37
As others have said check connections, 6B&S would have been better.

Some chargers will stop charging if the voltage drops, then check the input voltage again, if it recovers they assume the voltage drop is due to wiring loses and eventually will either ignore the drop or throttle back. Have you tried letting it run for some time to see if it adapts?
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Follow Up By: Frank P (NSW) - Saturday, May 04, 2019 at 22:22

Saturday, May 04, 2019 at 22:22
My method on my BT50 with a service canopy and aux battery in the canopy:

0 gauge +ve from starter battery through to a distribution board in the canopy close to where the battery is. 0 gauge -ve from distribution board to OEM chassis earth point close to starter battery. 8 gauge pos and neg from distribution board to the 25A DC-DC charger and from charger to battery (cable run about 1.5m total from charger to battery).

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Follow Up By: Kam - Monday, May 06, 2019 at 15:11

Monday, May 06, 2019 at 15:11
thanks guys, i found the problem, first i tested all connections and they were all good, then i followed the test suggestion by RMD, big drop on red cable but no drop on Black, so as you all suggested the 8B&S is probably undersized, even thou the charger manual recommends 8B&S upto 6 meters, even when i spoke to Projecta a while back, they send me a diagram with 8B&S black and red from main battery to the back and after many tests they asked me to do, they finally said there is a big resistance somewhere that i need to find and fix other than that everything looks fine.
since i already have a 4awg black cable, i am going to replace the red with a 4awg cable and set it up the way Frank has got his with the distribution board. i will let you know how the system works when i have the work done.
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Reply By: Member - FSH00 - Saturday, May 04, 2019 at 23:10

Saturday, May 04, 2019 at 23:10
May be of some interest.

http://www.home12volt.com.au/uploads/2/6/0/5/2605767/dc_chargers_and_the_alternatives_-_vehicle_charging.pdf
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Reply By: Zippo - Sunday, May 05, 2019 at 12:09

Sunday, May 05, 2019 at 12:09
The DC-DC charger has an IGNITION CABLE? It is meant to be connected to the IGN circuit so that operation occurs whenever the engine is running, but not otherwise - to save the cranking battery from undue discharge.

What - if anything - have you connected it to at this stage?
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Follow Up By: Frank P (NSW) - Sunday, May 05, 2019 at 13:36

Sunday, May 05, 2019 at 13:36
Follow-up deleted after reading RMD's Reply below
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Reply By: RMD - Sunday, May 05, 2019 at 14:23

Sunday, May 05, 2019 at 14:23
The dc dc unit you have is not an isolator in the true sense of the word. It's action is one of isolation but not anything like a solenoid isolator. A solenoid isolator either connects or it doesn't, according to voltage level.
The IDC25 with an ignition/ positive sense wire allows the dc dc unit to drag charge from the battery until it lowers to under 13volts, ie,12.7v approx if sense wire is NOT activated.

With the wire connected and motor running or stopped, the IDC25 most likely will continue to consume main battery until just below 12V. Suits those silly alternators. But if key on and motor stopped it will drag the main battery down to 12v. Not good to do that if main battery is valued, relied upon.
There is always total isolation between the input and output of an IDC25. So considering isolation to be factor is misleading seeing the technical aspects of modern electronics means a variety of possible situation.
Leave the wire off, you don't require that feature.
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Follow Up By: Allan B (Sunshine Coast) - Sunday, May 05, 2019 at 14:45

Sunday, May 05, 2019 at 14:45
.
Why would you have.... "key on and motor stopped"?
Seems not a good idea at any time.
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Allan

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Follow Up By: RMD - Sunday, May 05, 2019 at 16:43

Sunday, May 05, 2019 at 16:43
G'day Allan
Just mentioned it because it might happen sometimes with ign left on OR the owner may have a switch on that wire to a +ve source which acts as though the ign is On. Therefore the unit would still be active to the lower voltage level of main battery and depleting main battery charge reserve. On a freezing morning in camp up in high country with main down to 11.9 v and trying to start a glow plug assisted Diesel will be interesting with little punch in the battery.
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Reply By: Kam - Sunday, May 05, 2019 at 17:38

Sunday, May 05, 2019 at 17:38
thanks all, every one has shed some light on my problem, i will get on diagnosing the voltage drop as it really should not be happening with standard alternator anyway, i will consider every advice and test everything when i get the time in a day or so, one thing i noticed so far is that thru every cycle of start stop charge by charger, the charger push a little bit of current into the aux battery making the aux battery to take little bit of charge on every cycle and as the voltage of the aux battery rises over time, so does the input voltage at the charger until it reaches the 12.8 volt where the charger keeps the constant charge and more rapidly charges the aux until the aux battery is in full charge, but even when the aux battery is in full charge (the charger goes into maintenance mode) the input voltage at the charger remains at 13.5V while the car is still running and alternator is producing 14.4 volt. (the negative cable i have between the negative terminals of aux and main battery is marked 4awg and the red between main battery and charger and from charger to aux is marked 8awg)
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Follow Up By: Allan B (Sunshine Coast) - Sunday, May 05, 2019 at 17:47

Sunday, May 05, 2019 at 17:47
.
Just one question Kam, are the voltages at the different points all being read by the one portable multimeter...... or do you have some installed meters?
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Allan

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Follow Up By: Kam - Sunday, May 05, 2019 at 18:09

Sunday, May 05, 2019 at 18:09
Hi Allan, i use the same portable multimeter
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Follow Up By: RMD - Sunday, May 05, 2019 at 20:11

Sunday, May 05, 2019 at 20:11
Does the voltage at the main battery really stay constant or is it the same each time you check when the dc unit stops charging. If the alternators has a blown diode the battery voltage will reach it's normal regulated voltage, BUT under load the loss of 2/3 of current ability will see the loaded voltage of main drop to below the dc unit threshold and so it will then cycle on and off as the dc unit applies and disconnects it's inverter section as the main battery voltage level is discharged and then subsequently recharged. Without the dc unit in circuit, test alternator by turning on everything and see what voltage the alternator can hold the main battery up to. Sometimes the alt charge wire is too small in size and that also limits the output of alt to battery.
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Follow Up By: Kam - Tuesday, May 07, 2019 at 13:50

Tuesday, May 07, 2019 at 13:50
i was sure the main battery voltage stays constant at 14.4, but i run a test as you suggested, and it stays at 14.2 under load. so i assume the alternator is OK, right?
another question, when i upgrade the red cable from main battery to the distribution board at the back with a 2AWG (i am intending to upgrade to this size cable), what kind of fuse is available to fit at the main battery to connect this cable to? at the moment i have an 8awg inline fuse.
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Follow Up By: Frank P (NSW) - Tuesday, May 07, 2019 at 15:23

Tuesday, May 07, 2019 at 15:23
With the cable sixes you are talking, a bolt-down type type of fuse and holder such as this one by Redarc would be the best option, IMO. That one is expensive, but there are cheaper options - search on eBay or Jaycar for "bolt down fuse holder" and take your choice.

A quality circuit breaker is another option but they can be affected by engine bay heat. I had a 70 amp one in an engine bay. It continually popped with a 40 amp load. I now have a bolt down fuse.

Cheers
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, May 07, 2019 at 16:53

Tuesday, May 07, 2019 at 16:53
.
I absolutely agree Frank. Bolt-in fuses are the only way to go for high capacity applications.
....I like Redarc but 70 bucks for a fuse plus holder is outrageous.

Jaycar, Narva and others do the same for about $24.

And there is an even cheaper way for the fuse located at the battery. Use a fuse without the holder, attach one end to the battery post terminal and connect the other end to the cable with a lug and short 8mm bolt & nut. Cover the fuse with heatshrink. Voila.... less than $10 all-up. Totally reliable and fused right where it should be. And that is how mine are.

I originally had a quality(?) 60A thermal circuit breaker in the engine bay but it failed, not from heat, but from fine dust ingress. Now it's a fuse! But the same CB's on the cabin distribution board are OK. Here they are good as they also perform as isolator switches.

Blade fuses?????..... I have had two fail due to oxidised contacts in the last month. No current demand, one supplies a voltmeter the other a relay.
Both of these came from stock I purchased some time ago. Methinks I'll chuck the lot out and get new quality stock. Bolt-in fuses would be a bit of overkill here.

Cheers
Allan

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Reply By: Kam - Sunday, May 19, 2019 at 19:26

Sunday, May 19, 2019 at 19:26
Hi every one, problem solved, i upgraded the red cable to 2AWG with bolt in fuses and a distribution board at the back, perfect, no voltage drop, aux battery charges fast, when it is at 12v, it takes couple of hours to being fully charged and no need for the blue wire at IDC25 to be connected to ignition, it works as it should. thank you every one.
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Follow Up By: Frank P (NSW) - Sunday, May 19, 2019 at 22:05

Sunday, May 19, 2019 at 22:05
Good result, glad we could help.

Cheers
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