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Discussion Starter · #1 ·
Please be patient as this may sound stupid.....

I have a dual battery system and need to understand more on how it works. This is how I think it does so correct me if I'm wrong.

The controller is a db something...not real important for my q.......

My crank battery has to be up to a certain voltage before the controller directs current to the aux....as indicated by small green LED in controller. If the crank battery is fine then there is no prob but....what if it starts failing on a trip?? It's dated 2005 so has lasted pretty well so far. If it starts to fail and not get to the correct voltage...well that means none to the aux supplying power to the fridge.
Now my question is....in this situation, as long as the engine is running, can I link the two with a jumper lead in order to charge the aux?

If I can't do this, are there any other options while out bush apart from running the fridge off the main batt while the engine is going of course?

thanks for your help.....
 

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thats roughly right. however your main battery only gets up to voltage when engine is running ie alternator is charging. if your running high loads and battery voltage drops then aux battery will not get charged.
if the battery is dieing it can not accept charge and voltage will be high so aux battery will charge. however if main battery is shorting internally then it will draw more power, combined with other loads can drop below required voltage and aux battery won't charge.

putting a jumper across may not charge it up as voltage isn't above aux battery voltage.
 

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Discussion Starter · #3 ·
thanks tweak'e,

I'm assuming that the voltage in the aux would be low by the time I find out it's not charging so the output of the alternator would be greater of the 2....thats my theory anyways.
Will go and get the crank batt load tested anyway just to see how it is....
Hope you are not in chch....I was born there and have a lot of family still there...all ok apart from one house that needs some repairs.....

thanks again
sneezy
 

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The Bear
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posting this in 2 parts.
1. Buy a small genny and a batt charger for "out bush" or a solar panel for the aux batt and emerg charging of start batt.

2. You will see that after you stop your engine the "green charge indicator light" on the VSR stays on so both batteries are still connected till the start battery voltage drops below VSR switch threshold then turns off. Theoretically whilst connected if the aux batt is fully charged and the start is failing the aux should hold the VSR closed (active) till the aux bat drops to the opening voltage of the VSR - unless there is a huge diode in there to prevent back current- I doubt it - because the VSR is sensing the voltage level from the aux battery whilst both batteries are connected, and when it closes the voltage level in the aux battery will still be high but the start batt voltage will continue falling till its flat. You can test that theory by putting a battery charger on your aux battery and start the engine till the charge light comes on on the VSR then turn the engine off, the VSR charge light should stay on because it should be detecting the higher voltage in the main battery back through the VSR from the Aux because of the battery charger.

Okay just did the experiment instead of theory, My VSR is a 140 amp marine one from BEP cut in voltage 13.7 cut out voltage 12.8v.

TEST start main batt 12.66 volts at rest, aux 12.9 v at rest. Connect 25 amp ctek batt charger to aux batt and turn on aux batt goes to 14.06V on charge, start engine and rev motor alt cuts in and VSR kicks in main battery charging at 13.62V on alternator slowly rising, aux still at 14.06v. turn engine off, battery charger still on, start batt at 13.67 and rising, aux at 14.05v VSR still active. Turn battery charger off, after three minutes main battery at 12.75V, aux at 12.9v VSR still closed, after 5 minutes main at 12.72v (below cut out voltage of VSR), aux at 12.9v, VSR still active, 7 minutes main batt12.69v, aux 12.9v, VSR still active, 8 minutes main at 12.67v, aux at 12.9v VSR still active. I then turned the VSR off ( got a sw in the earth line of VSR) and back on again VSR relay dropped out because main batt voltage too low to activate, main batt 12.67v, aux still at 12.9v.

That definately shows that the aux batt was holding the VSR closed (active), but the higher voltage of the AUX battery at rest of 12.9 was not sensed at the start battery (12.67v) after the battery charger was turned off. Voltage losses between front and back varied between 0.15v and 0.34v.

So there is no back current flow in the actual voltage sensing circuit of the VSR after the main battery drops below the switching threshold, but the relay is held closed and charge flows back to the start battery from the battery charger, battery charger off, current back flow drops but VSR relay still held open for a time, I would suggest till the aux battery drops below 12.8v, didn't test that would take too long as its still at 12.9 at rest after 8 minutes. Probably drops out after 10 mins or so.
 

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The Bear
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If the start battery "collapses" overnight then you will have no warning as it probably faulted during our driving day and the alternator made up for it, when the ign is off and the start battery voltage dropped below sensor threshold the VSR relay will safely isolate your aux, so its full all the time.(volt meter)

If you have an aftermarket volt meter, a cheapie digital from jaycar will do the job you will detect a "failing battery" long before it "collapses", because before you start in the Am you will notice that the voltage is down on the main because it is not holding charge overnight, and voltage in the aux will probably be higher. Plus the starter will be noticably lazy, headlights dim quickly with engine off.

If you have the Aux in the engine bay you could make a short lead to go directly from the alt output to your aux, or if the aux is in the back and your VSR is in the engine bay then from the alt output directly to the aux charge output on the VSR so it charges the aux bat directly, but you would have to disconnect the start bat because it would suck the life from the aux in short time when you stop because both batteries are directly connected at the alt terminal, that defeats the purpose of the VSR in the first place, unless you put an inline hd breaker/switch in the EMERGENCY charge line between the alt and the VSR OUTPUT, AND REMEMBER TO TURN IT OFF BEFORE YOU TURN THE ENGINE OFF.

All that's a bit of a work around for an emergency but a PIA none the less, better to get your start bat load tested and replace if in any doubt. I use delkor calcium 710 CCA as the start bat as they take a quick charge well, are maintenance free, and have good reserve capacity, and my aux bat (Gel AGM) is in the back of the wagon. Have had to pull it out a few times to jump start the the old delkor died after about 6-7 years.

I would suggest you doing the same test on yours, take rest voltages, then battery charger on aux battery take charge voltage, turn engine on, rev to activate VSR, take main batt voltage, turn engine off, wait then take voltages again, turn battery charger off check voltages again every minute or so till VSR drops out. only takes 10 minutes or so.
 

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Discussion Starter · #6 ·
RosieBear,
Just went out and connected up as stated.
Main batt at rest 12.13
aux 12.45

Started car and main went to 14.24 on fast idle and was slowly rising in Volts
no change in aux

After over 5mins main was 14.47 and the isolator still hadn't kicked in.

gave up.

There is no load on aux. Only connect fridge when needed which is only once or twice a year (unfortunately). The controller is a Piranha dbe 150-s mkII.

Solar panel looking good at the moment.

Thanks for your help
sneezy.
 

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The Bear
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Sounds very much like your Pirana whatever it is, isn't working or wired up wrong, maybe earth not connected, I would get something simpler, like a BEP VSR from a marine reseller, like Bias Boating., reasonable price, and reliable.
 

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Discussion Starter · #8 ·
are they that easy to wire up as the website seems to imply??

if so, I may look at one real soon.
 

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LED ZEPPELIN
1995 GQ TD42 NA
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Yep dual batteries are easy to wire especially if you get the ABR Sidewinder kit (from Derek Bestem, he is on ebay).

If you have 12.13v at rest on your cranking battery I think you have a problem there - should be 12.8 or so.
 

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Discussion Starter · #10 ·
Thanks for the info Squalo, I'll check them out. A bit more info regarding my crank batt.......the 12.13v was taken first thing on sunday morning after sitting most of sat arvo/night. It build date is 2005 but still starts the truck first crank every time....but once it's going and charging, I still think the led on the dual batt controller should come on so suspect a prob with that as well.

thanks again
 

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LED ZEPPELIN
1995 GQ TD42 NA
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Here's the ABR unit:

DUAL BATTERY ISOLATOR ABR SIDEWINDER DBi140 *NEW MODEL* | eBay

I found Derek while researching dual battery kits and was impressed by a) his knowledge and b) his willingness to share it. I'm always happy to give my money to a vendor like that. Whatever electrical work you are planning it's worth reading up on it at his website:

ABR - SIDEWINDER

Just measured my batteries now after sitting overnight, main is the original one so three years old now and it was at 12.5v. Second battery is less than six months old and was 12.7v
 

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Sounds very much like your Pirana whatever it is, isn't working or wired up wrong, maybe earth not connected, I would get something simpler, like a BEP VSR from a marine reseller, like Bias Boating., reasonable price, and reliable.
Had the same problem with the same Piranha unit a while ago. Was fitted by Piranha in their shop in Melbourne so fitting was correct. Worked for a couple of years then started to play up. Could hear the relays click in and out but would not stay on.

Emailed Piranha but no response. Opened it up and it is definitely not a properly sealed unit and showed bits of corrosion. Chucked it in the bin and replaced it with a Redarc. Kept the battery monitor and wired it into the Redarc. Works great - no more problems!

Conclusion: Piranha unit is expensive, unreliable and their customer service sucks!

So I agree, get something more simple. The other thing I like about the Redarc is the option to override the unit and connect both batteries in case of flat start battery: pushing a button to temporarily connect is easier and quicker than using jumper leads!!!
I actually used a momentary push button with built-in LED from Jaycar so the moment the Redarc cuts in there's a light on the dash.
:D:cool::)
 

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Discussion Starter · #13 ·
Here's the ABR unit:

DUAL BATTERY ISOLATOR ABR SIDEWINDER DBi140 *NEW MODEL* | eBay

I found Derek while researching dual battery kits and was impressed by a) his knowledge and b) his willingness to share it. I'm always happy to give my money to a vendor like that. Whatever electrical work you are planning it's worth reading up on it at his website:

ABR - SIDEWINDER

Just measured my batteries now after sitting overnight, main is the original one so three years old now and it was at 12.5v. Second battery is less than six months old and was 12.7v

Thanks Squalo.....got the 120amp one already on the way.....:D
 

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Discussion Starter · #14 ·
Installed the new isolator yesterday and it all works fine. Had the crank batt tested by an auto electrician and he was surprised I think by how strong the battery is for being stamped 05. No probs with it or the deep cycle so am wrapped with the outcome.

Thanks for all your input and advice
sneezy
 
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