Smart dual battery isolators not so smart?

Submitted: Wednesday, Jun 10, 2009 at 17:09
ThreadID: 69687 Views:9336 Replies:13 FollowUps:19
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It seems there may be some misconceptions out there as to how a smart system (redarc, etc) actually charges the battery..
Firstly I am not a sparky but have now discussed this with a few..
A dual battery system promises to
1)charge the cranking battery first
2)then charge the aux battery
3)isolate the starter battery when ignition is off, power from au only

Now I understand item 3) above, it is items 1) and 2) that are grey. The 'promise' on the ads is that ALL the charge go to the starter battery, after which ALL the charge go to the aux. That also enables you to have dissimilar batteries as they are not in parallel

Right? Apparently not! Yes the charge go to the cranking battery, but when that is full the aux battery is simply 'hooked on' to parallel. There is no such animal as ALL the charge going to the aux battery only. As a non-sparky this actually makes sense as the isolator thingy is 'downstream' from the main battery, so surely it can't receive ALL the charge in isolation from the main? The chatge from the alternator goes by cable to the main then to the aux, there is no cable to the aux without going through the main first?

I hope I am wrong, as one of the main reasons I want to split my current factory fitted twin batteries was so I can install an AGM as aux and not worry about dissimilar batteries charging in parallel

Can someone please shed some light (provide a spark!) in plain English as I am confused

Cheers

CJ
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Reply By: Member - Norm C (QLD) - Wednesday, Jun 10, 2009 at 17:30

Wednesday, Jun 10, 2009 at 17:30
CJ, you pretty much have the important facts right in terms of how most of these systems work.

But there is no need to worry. Despite fears held and repeated by some people about charging dissimilar batteries in parallel, there is little to worry about. Just do it.

I have been using AGMs as aux batteries for over four years. I currently have five AGMs used as aux (3 in van and 2 in vehicle - one of which is in engine bay). I have never had a problem and one of the AGMs in the vehicle is now over 4 years old.

There are many 'old wives tales' about 12 Volt batteries. In my view, you have been told one of them.

Norm C
AnswerID: 369350

Reply By: Lex M (Brisbane) - Wednesday, Jun 10, 2009 at 18:21

Wednesday, Jun 10, 2009 at 18:21
3)isolate the starter battery when ignition is off, power from au only


There's been a fair bit of discussion recently about this misconception also.
Some (most) voltage sensing isolators keep the batteries connected for some time after engine stopped, ignition off until the main battery voltage drops.
AnswerID: 369362

Reply By: tim_c - Wednesday, Jun 10, 2009 at 18:35

Wednesday, Jun 10, 2009 at 18:35
1) generally the "smart" systems keep the batteries isolated until the main battery reaches a pre-determined voltage level ie. charged
2) at this point, the second battery is electrically connected. Since the main battery is theoretically charged, it should not accept any further charging current to maintain the required voltage, therefore all remaining current should go to the second battery at this time.
3) This is the most important aspect - the whole point of having a second battery!

As someone else said, many of the so-called "smart" systems leave the batteries connected after the engine has been shut off, until the batteries drop back to the pre-determined voltage level. Some even click in and out sevel times a second if the aux battery is being used. This is because the load on the aux battery causes the voltage to drop. If it's still connected to the main battery, the main battery voltage drops too causing the system to isolate. This then relieves the main battery so the voltage increases again and the "smart" solenoid then reconnects the batteries and this process repeats... very bad for both batteries.

When I wired in my system, I did it in a far simpler way - they were isolated when the engine wasn't running (even if ignition was on) and they were connected as soon as the engine started. If you wanted to get fancy, you could add a timer so the batteries connected a certain time (ie. a couple of minutes) after starting the engine giving the main battery a chance to be topped-up after starting the engine before connecting the aux battery. And still isolate as soon as the engine is turned off.
AnswerID: 369366

Reply By: ABR - SIDEWINDER - Wednesday, Jun 10, 2009 at 19:07

Wednesday, Jun 10, 2009 at 19:07
Hi CJ

Well spotted and this thread will clear up your worries. We are working on this issue and fingers crossed will have our new isolator available by the end of the year.

We have decided to redesign the battery isolator from scratch and have a worked out a way using 3 integrated circuits to switch the alternator and not the batteries but still supply enough current to the main battery to run the car electrics. Load demand will shift the alternator back to the main battery should the load be greater than circuit 3 is supplying back to the main battery and once the load is reduced it flips over the other way again. All done with a 3 minute dwell to prevents any surges and spikes.

Regards

Derek from ABR
AnswerID: 369379

Follow Up By: olcoolone - Wednesday, Jun 10, 2009 at 19:24

Wednesday, Jun 10, 2009 at 19:24
Is it going to work with smart alternators thats controlled by the ECU.
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FollowupID: 636802

Follow Up By: ABR - SIDEWINDER - Wednesday, Jun 10, 2009 at 19:32

Wednesday, Jun 10, 2009 at 19:32
Yes, we had to increase the dwell time from 1 minute to 3 minutes to overcome this issue.

Our only issue may be with the new 48V systems but that will be a new system altogether.

Regards

Derek
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Follow Up By: Member - Mike DID - Wednesday, Jun 10, 2009 at 23:25

Wednesday, Jun 10, 2009 at 23:25
The change to 48 volt systems was promised many years ago but just hasn't happened.

The arcing when trying open a breaker in a 48 volt systems causes too many problems.
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FollowupID: 636855

Follow Up By: olcoolone - Sunday, Jun 14, 2009 at 13:20

Sunday, Jun 14, 2009 at 13:20
48 volts has been droped, manufactures are going to better load sharing technology.

The main reason 48 volts got the can was it could not do everything they wanted it to do and the onset of 200 to 600 volt systems in Hybrids that can do everything they want it to do..



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Reply By: Sand Man (SA) - Wednesday, Jun 10, 2009 at 19:24

Wednesday, Jun 10, 2009 at 19:24
CJ,

Your assumption is not correct for some smart isolators, according to advice I received from Piranha.

The main starting battery is always protected and cannot be drained by a load connected to the auxiliary battery.

Once the controller has determined that the primary battery has reached a certain voltage, it switches in the auxiliary circuit to enable charging of the second battery.
The two batteries however remain electrically isolated from each other and a load applied to the auxiliary battery will not affect the primary starting battery in any way.

Other makes of Controllers may well perform differently, but are they Isolators, or merely Controllers.


Bill.
Bill


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AnswerID: 369384

Follow Up By: tim_c - Wednesday, Jun 10, 2009 at 20:20

Wednesday, Jun 10, 2009 at 20:20
Maybe I'm missing something here but I don't see how you can switch in the aux circuit to charge the second battery while both batteries remain electrically isolated from each other - unless the main battery is disconnected from the charging circuit whenever the aux circuit is switched in? By connecting the second battery to the charging circuit of the car, it is therefore connected to the main battery (since the main battery is usually permanently connected to the car circuit)
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Follow Up By: olcoolone - Wednesday, Jun 10, 2009 at 22:28

Wednesday, Jun 10, 2009 at 22:28
When the ignition is turned off both batterys will still be connected until the total voltage drops to 12.6 volts.

When 12.6 volts is reached the smart solenoid separates the start and aux battery.

As all your ignition off loads should be of the aux battery...this then leaves the start battery to do it's job (starting the vehicle).

When you start your vehicle the the solenoid will keep the start battery and aux battery isolated from each other until the start battery reaches 13.1 volts.

When it reaches 13.1 volts both batterys are rejoined.

The Redarc Smart solenoid works very well and is very simple to install and use.

The Redarc Smart solenoid is a lot cheaper then most of the other electronic isolators on the market.

The simple answer is it woks well and there are thousand being used around Australia.

It's like most things in....theres not one thing wich is good at everything....theres always a comprimise.

If you want to get the best run a Ranox.
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Follow Up By: Member - Stuart P (WA) - Wednesday, Jun 10, 2009 at 22:47

Wednesday, Jun 10, 2009 at 22:47
if the start battery is at a pre determined voltage ie 14.2 v and the relay switches over the battery with the least charge will take more of the charge from the alternator . if you have a dual battery set up and you have an open circuit battery in the system and a good battery in the same system the charge will tend to charge the open circuit battery first because of its lower resistance and drain the main battery at the same time.
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Follow Up By: olcoolone - Thursday, Jun 11, 2009 at 10:21

Thursday, Jun 11, 2009 at 10:21
And?

What are you saying...
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Follow Up By: Member - Stuart P (WA) - Thursday, Jun 11, 2009 at 23:13

Thursday, Jun 11, 2009 at 23:13
do you want a manual or automatic setup?
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FollowupID: 637000

Reply By: Von Helga - Wednesday, Jun 10, 2009 at 21:08

Wednesday, Jun 10, 2009 at 21:08
CJ
My Redarc is connected to the post on the alternator where the main battery cable is connected to so it is not after the main battery (in circuit terms) so it can actually switch the Aux on and off from the main circuit based on what it reads in the main circuit.
Cheers
Trevor
AnswerID: 369411

Reply By: Peter_n_Margaret - Wednesday, Jun 10, 2009 at 21:41

Wednesday, Jun 10, 2009 at 21:41
Watch out for a spectacular new RedArc product especially for caravans and campers due 1/7/09.

Cheers,
Peter
OKA196 Motorhome
AnswerID: 369422

Follow Up By: olcoolone - Wednesday, Jun 10, 2009 at 22:31

Wednesday, Jun 10, 2009 at 22:31
You must be talking about their new DC-DC charger.
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FollowupID: 636844

Reply By: Maîneÿ . . .- Wednesday, Jun 10, 2009 at 21:42

Wednesday, Jun 10, 2009 at 21:42
CJ,
ROTRONICS make a battery Isolator that WILL charge the Auxiliary (Deep Cycle) battery Directly by the Alternator, with-out having the Cranking battery in the same charging circuit, so you are charging the Deep Cycle battery system independently.

The Cranking battery is charged and is then Isolated from the alternator.

Maîneÿ . . .
AnswerID: 369423

Follow Up By: Member - Matt M (ACT) - Friday, Jun 12, 2009 at 11:45

Friday, Jun 12, 2009 at 11:45
So what provides service power to the vehicle then?
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FollowupID: 637057

Follow Up By: Maîneÿ . . .- Friday, Jun 12, 2009 at 14:41

Friday, Jun 12, 2009 at 14:41
This link: Rotronics charging system has information on how the Auxiliary battery is recharged Directly by the Alternator.
The Main battery is topped-up for the vehicle restart and then Isolated from the alternator and the vehicle power supplies.

Maîneÿ . . .
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FollowupID: 637074

Reply By: CJ - Wednesday, Jun 10, 2009 at 22:04

Wednesday, Jun 10, 2009 at 22:04
Guys,

Thank you all for your replies. It has cleared a few things up for me, I hope it has been of use to others

CJ
AnswerID: 369425

Reply By: Member - Phil G (SA) - Wednesday, Jun 10, 2009 at 22:28

Wednesday, Jun 10, 2009 at 22:28
If you want to isolate your ?100series TD twin batteries, then you have two options:

#1 Simply fit a battery kill switch between the two batteries. Keep them joined most of the time. If you are camped more than one night, you might want to lift the bonnet and flick the switch to isolate them. The modern fridges don't use much power these days. This option costs $20 and works more reliably than any of the flash (???Smart) isolators. But none of the 4wd shops will sell this because they won't make money. Best to have two identical batteries (eg Exide Extremes) for this setup.

#2 Buy a seriously Smart isolator - eg Rotronics MH10 that will cost twice as much as a Redarc not-so-smart isolator. It is hooked into the IGN circuit, so the batteries are isolated when you switch the motor off. Costs about $300 for the isolator. Can use dissimilar batteries with this setup.

I personally favour #1 for a 2 battery system with my style of camping/4wding. I drive the vehicle every day and twin batteries crank nicely and last a long time. If you stay put for a couple of days, or really want an AGM, you might prefer option #2.
AnswerID: 369431

Follow Up By: CJ - Thursday, Jun 11, 2009 at 09:15

Thursday, Jun 11, 2009 at 09:15
Wouldn't this option cause a spike and potentially damage one of the many computor/ECU/etc?
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FollowupID: 636881

Follow Up By: Member - Phil G (SA) - Thursday, Jun 11, 2009 at 09:40

Thursday, Jun 11, 2009 at 09:40
Gday CJ,

The only way I know of to cause a spike would be to turn the switch and isolate a depleted battery while the motor was running at high revs.

Given you have to stop and lift the bonnet to flick the switch, and that there is no need to isolate batteries when the motor is running, I can't see it ever happening. I also think modern (Japanese) vehicles have sufficient spike protection these days.

Cheers
Phil
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FollowupID: 636886

Reply By: Jimmywhisker - Thursday, Jun 11, 2009 at 06:19

Thursday, Jun 11, 2009 at 06:19
CJ,

One problem I had was, when the main battery was totally dead, there wasn't even enough charge for the smart battery system to switch over to run the aux in parrellel. I had to install a manual override switch as the smart battery system was connected to my standard 12v electrics. This works well though and a good backup nonetheless.

In my case, I have a number of auxiliary power points throughtout the vehicle that run directly of my deep cycle auxiliary battery and those outlets run irrespective of the key position. This works really weell as I have a light permanently plugged in whenever I am on the road.

Other than that, no problems with parrellel charging after many years. It does take quite a drive to get them both charged so I always leave home after leaving them on the 240V charger overnight.

Good luck.

Peter
AnswerID: 369446

Follow Up By: olcoolone - Thursday, Jun 11, 2009 at 10:29

Thursday, Jun 11, 2009 at 10:29
The purpose of the Smart solenoid is to ensure the start battery always has a charge before the aux.

The Smart solenoid is designed to protect the start battery from being run flat.

Thats why they have a manual override incase your start battery goes flat.














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FollowupID: 636902

Reply By: Member - Mary W NW VIC - Thursday, Jun 11, 2009 at 20:58

Thursday, Jun 11, 2009 at 20:58
Now I am totally confused-pretty electrically challenged for a start
Perhaps someone can help
Had a rotronics duel system fitted -seemed to work as intended
have a national lunar volt meter connected which shows volt condition of both batteries with a low vlotage alarm
last year alternator had a problem was reconed-batteriies didn't seem to retain charge at the level noted before-no leakage detected by auto elec
Suggesteed redarc was fitted.now batteries seem to charge simultaneously as i suppose is intenede -ie 2 separate solenoid clicks audible but my confusion is that in the morning both batteries seem to be equalisedat the same state .Ie crank and aux seem to draw downto same voltage
WHat's wrong?
At least rotronic system would reflect usage ie frig on aux
this way it's just both batts down to danger level overnight.
???
Please make replies in as easy to understand language as possible'
Thanks,
Mary
"Some people walk in the rain,others just get wet."

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AnswerID: 369577

Follow Up By: Maîneÿ . . .- Friday, Jun 12, 2009 at 10:23

Friday, Jun 12, 2009 at 10:23
Mary, as I understand your post it goes like the following:

1. You had Rotronics dual battery system (model unknown) it worked as intended!

2. Faulty Alternator reconditioned!

3. Since recon Alternator fitted batteries won't "retain charge"!

4. Rotronics system removed and Redarc fitted!

Your say: "in the morning both batteries seem to be equalised at the same state, ie Crank and Aux seem to draw down to same voltage - what's wrong"



Mary, depends on what the battery Voltage is in the morning?
if it's below the 'cut-out' voltage of the Redarc I would suggest the Redarc is faulty, if it is not then everything is ok.
(Note: different model Redarc have different cut-out Voltage)

* If the Voltage is too low to start the vehicle there is (still) a problem.

* What did you do with your Rotronics system ?

Maîneÿ . . .

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FollowupID: 637041

Reply By: Member - Mary W NW VIC - Friday, Jun 12, 2009 at 21:30

Friday, Jun 12, 2009 at 21:30
Hi mainey,
The overnght voltage of both batts is barely 12 volts now frig will cut out if left on for more than 12 hrs.Previously would get 2 days from aux without starting engine.Since the alt problem seemed to be losing charge but no leakage detected by 2 different testers.Am running delco calcium batts and even replaced these.Auto elec suggested Redarc but i feel that all it does is equalise voltage between bat and not really isolate crank at all,Always seem to be able to start but it's a bit slow sometimes.
This still occurs ater a drive of over 300k's .Do you think it's an alt problem?
Cheers,
mary
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AnswerID: 369741

Follow Up By: Maîneÿ . . .- Saturday, Jun 13, 2009 at 09:28

Saturday, Jun 13, 2009 at 09:28
Mary,
Can you remove, or at least disconnect, the fridge from the 12v battery system for a few days?
(or leave it there and just turn it off)

Do you know the Voltage of the 'Cranking battery' and also the 'Aux battery' measured when the vehicle engine is running faster than idle (both batteries should be connected in parallel by the Redarc and should be registering the same charging Voltage) then measure the 'rested' Voltage of both batteries at least 3 hours after a reasonable drive.

Hope you did not leave your Rotronics system with the Auto sparky :-(

Maîneÿ . . .
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FollowupID: 637185

Follow Up By: Member - Mary W NW VIC - Saturday, Jun 13, 2009 at 11:41

Saturday, Jun 13, 2009 at 11:41
Yes I did leave it there and will check voltages and post later
Thanks,Mary
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Follow Up By: Maîneÿ . . .- Saturday, Jun 13, 2009 at 11:51

Saturday, Jun 13, 2009 at 11:51
Wonder who he sold it to ???
I suggest that because it looks like it may have been 'ok'

Maîneÿ . . .
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