Caravan Batteries

Submitted: Monday, Jul 25, 2005 at 09:38
ThreadID: 25021 Views:3711 Replies:28 FollowUps:21
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Hi.
I have heard that one of the best ways to charge a DSB mounted in a caravan is via an inverter and battery charger. The inverter being powered from the tow vehicle. Any thoughts on this? I am led to believe that this system is more efficient that any of the standard isolator type systems. Any advice would be greatly appreciated
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Reply By: pjchris - Monday, Jul 25, 2005 at 10:58

Monday, Jul 25, 2005 at 10:58
Absolutely true...Or use solar panels and a regulator.

Reasoning is this: The length of cable from the car to the caravan battery causes voltage drop. Also many caravans have a protection diode fitted so the caravan battery won't discharge back in to the car. this all means that you wil probably lose at least .6 volts (Diode alone) to 1-1.5 volts (Added loss in wiring to Diode) which means that the voltage at the Caravan battery will, in all likelihood, be between 13.4v and 12.9v (Assuming the alternator produces 14.4v). This is not enough to fully charge the caravan battery.

Peter
AnswerID: 121895

Reply By: Member - Chrispy (NSW) - Monday, Jul 25, 2005 at 11:05

Monday, Jul 25, 2005 at 11:05
I'm very interested in this thread too.

OK - given that you are charging a caravan battery with a charger coming off an inverter - how big has this charger got to be??????

An isolator will give you a fair few amps more than your average "affordable" battery charger won't it? I have a battery charger that I paid a bit for a while ago - and off 240V it can only muster 8 amps... which isn't going to re-charge my 105A/H van battery withing a day's driving....
AnswerID: 121896

Reply By: drivesafe - Monday, Jul 25, 2005 at 13:03

Monday, Jul 25, 2005 at 13:03
Right on the money Chrispy, for a start, to be able to get the correct current and voltage to the van to run the inverter properly, you will have to install huge cables from the front of the tow vehicle to the inverter in the caravan or camper trailer.

Even then as Chrispy has pointed out, unless you have a large battery charger, it is still going to take forever to charge the battery.

As for the diode in the caravan, I think you will find this is more to do with a given type of battery isolator and not the specific installation of a diode in a caravan, haven’t come across that one.

Forget the inverter + battery charger idea. For a fraction of the cost of a large battery charger, you can install heavy cables in the first place and this alone will dramatically speed up the charging of the rear battery and the sooner a battery is charged the more likely it is going to be fully charge while you travel from one camp site to the next.

Cheers.
AnswerID: 121923

Reply By: fourplayfull - Monday, Jul 25, 2005 at 14:55

Monday, Jul 25, 2005 at 14:55
Hi Ray ,
I have set up two systems same idea as drivesafe and they work fine .
Run heavy cables from aux. batt thru' 50 amp andersons to same heavy cable to ct batts.
Important : when at campsite , keep aux. hooked up to ct . if you need to park parallel to ct I use extn. cable with andersons from front of 4by - this keeps aux. & ct batts.even charge .
: aux. & ct batts must be similar ie all wets , gels or AGM to facilitate more efficient recharging - I use 2- 12v x 120ahr.in ct & 100ahr optima as aux.
I get nil voltage drop when rested or charging - runs 80 litre engel & lights no probs.

CYA John
AnswerID: 121935

Follow Up By: Wizard1 - Monday, Jul 25, 2005 at 16:26

Monday, Jul 25, 2005 at 16:26
Does that mean you are re-charging your camper trailer (I assume that is what ct stands for) from your vehicle's auxilary battery without passing through any sort of charge control device?

Wizard
Prado TD
Gold Coast.
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FollowupID: 377097

Reply By: Member -Dodger - Monday, Jul 25, 2005 at 16:54

Monday, Jul 25, 2005 at 16:54
Get a twin charge unit from the 12volt shop and you will have no worries about voltage loss.
see this site
www.allabout12volt.com.au

The unit is called an...... ARID twin charge, it is purpose built to charge a van battery from the vehicle.
I used to have a handle on life, but it broke.

Cheers Dodg.

Lifetime Member
My Profile  Send Message

AnswerID: 121947

Reply By: Magnus - Monday, Jul 25, 2005 at 18:00

Monday, Jul 25, 2005 at 18:00
Hi Ray,

There is a considerable amount of material on the INTERNET that says a Deep Cycle Battery can not be fully charged from a vehicle alternator. They do not put out sufficient voltage nor the amps in a fashion suited to a deep cycle battery.

Also there is the issue that a deep cycle battery needs a three stage charger designed for the Deep Cycle style of battery.

The inverter, battery charger set up is quite a common approach to fully charging a deep cycle battery in a van or CT.

You will probably have both of these items in any case, so it could be just a case of using existing gear and adding some decent cabling.

Cheers

Magnus
AnswerID: 121956

Follow Up By: drivesafe - Monday, Jul 25, 2005 at 19:50

Monday, Jul 25, 2005 at 19:50
Hi Magnus, this not being able to charge an automotive battery, any automotive battery, not just deep cycle batteries, is a myth.

Provided you can get 13.8 volts or high, to the battery, there is no reason why you can’t fully charge the battery.

Don’t take my word for it, go to the different battery manufacture’s web sites.

I think this myth has come about by either people note reading battery stats properly or manufacturers not giving clear and simple data about recharging batteries.

There is an advantage to charging a battery at a high voltage, but it is more about shortening the recharge time not about getting the battery fully charged.
Go to the web sites and check the data for yourself.

Cheers
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FollowupID: 377141

Follow Up By: Magnus - Monday, Jul 25, 2005 at 21:46

Monday, Jul 25, 2005 at 21:46
Hi Drivesafe,

The sites I normally rely on for Battery info are

Darden

and

Arizona

plus a variety of other sites. The main issue appears to be the voltage requirements of Deep Cycle batteries in their charging phase exceeds the rated output of most car alternators. The output from my Mazda Tribute is right at the bottom end of the charging requirements for the average Deep Cycle Battery.

So, that is where I am coming from.

I do use an inverter and a charger, but I have those in any case for other purposes. So, for me it suits and appears to work well. Have done the cabling bit correctly with the right size and for the inverter with two cables to the main battery etc etc.

There certainly appears to be many different ways of going about powering up a Camper Trailer or Caravan or a Truck for that matter. And they all seem to work at least well enough to satisfy the owners.!

Cheers

Magnus


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FollowupID: 377165

Reply By: Flash - Monday, Jul 25, 2005 at 19:13

Monday, Jul 25, 2005 at 19:13
The inverter/charger idea DOES work well, very well.
BUT you need a large pure sinewave inverter, larger than you'd think due to an inductive load.
However, IF you have a large enough inverter hooked up to a three stage charger it works a treat.
AnswerID: 121978

Follow Up By: drivesafe - Monday, Jul 25, 2005 at 19:39

Monday, Jul 25, 2005 at 19:39
Hi Flash, I agree with you in that you posted the need for a very large inverter and charger. This is the problem, how many people would have a 25 amp battery charger and then have an inverter big enough to continually power the charger. Then add the size of cable needed to get a sufficiently high enough current at any where near a reasonable voltage, you would need substation grade cable to get it to work properly and then there is the efficiency question. Your alternator is now going to be flat out just trying to keep up with the current required by the charging system before it powers any thing else.

Nothing beats your alternator supplying the charge current directly to you rear battery via decent sized cable.
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FollowupID: 377139

Follow Up By: Flash - Thursday, Jul 28, 2005 at 12:01

Thursday, Jul 28, 2005 at 12:01
No, it's not as bad as it sounds.
I have helped set up such inverter/charger systems on a couple of vans where they already had the inverter- very little extra expense. Your vehicle alternator should handle the load as long as you don't have a humongous charger (The two I helped set up were both 25 Amp. I believe the current draw from the alternator is then probably less than 35 amps (ie: the 25 amps plus inefficencies in the inverter and charger- both usually better than 85-90% efficient.)
Where your alternator on it's own does a less than perfect job is in two areas:
1.it is only a "single stage" charger which works by regulating constant voltage- typically 13.8-14 volts. This will virtually never FULLY charge a Deep cycle battery (takes a long, long time).
2. That is dramatically further compounded by the fact that you get voltage drop when running low voltage all the way from your engine back to your Caravan - even as little as 0.25 volt drop means very poor charging indeed.

Having said that, you can still get reasonable charging from your alternator with heavy cables- BUT only if ANY other load- say a 3 way fridge- is ON A TOTALLY SEPARATE CABLE all the way from the alternator. This avoids the ineviable voltage drop caused by the fridge from affecting your batteries chargng. (As your batteries charge, voltage rises, current will drop and therefore voltage drop will become less and less. If however you have a fridge running off the same circuit, the voltage drop will remain and you will never successfully charge your caravan /aux batteries.) I cannot emphasise enough that load items such as a fridge must be on a separate cable.
I have helped many people set up such systems who then get reasonable (not outstanding) battery charging from their vehicles alternator. Only real cost is that of the cable and connectors/ relay or switch.
Cheers
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FollowupID: 377682

Follow Up By: drivesafe - Friday, Jul 29, 2005 at 19:27

Friday, Jul 29, 2005 at 19:27
Hi Flash, as before, I agree with your post but I would like to raise two points.

That is one big charger and if it did not charge the battery quicker to a full charge then there would be some serious problems BUT how much is a charger of that size. This is the point I keep trying to make, the Inverter/charger set up will work but at what cost compered to simply installing a second battery that would give you a greater stored capacity and to this end, I am aiming my argument at people who are looking at setting up a system from scratch.

The second point relates to the fridge being on the same cable. Why not, unless there is something very wrong with the fridge, it will normally cycle and during the off cycle, the battery can take the higher voltage, but being completely honest, the operation of the fridge would lengthen the full recharging time but a full battery is still very feasible.
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FollowupID: 377948

Follow Up By: Flash - Friday, Aug 05, 2005 at 23:43

Friday, Aug 05, 2005 at 23:43
1. Many peope have 20 and 25 amp chargers installed in vans- very common indeed. (Mine had a 25 amp "Truecharge" as part ofthe "package".) If it's there, then why not use it......
2. A compressor fridge will cycle- maybe as high as 75% or more running time in hot weather. While it's running you won't get much charge at all.
A 3-way fridge however DOES NOT cycle on 12v. You will not get any effective charge if you try to do so off the same cable. None.zero.zilch.Too much voltage drop.
Cheers
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FollowupID: 379001

Reply By: cmilton54 - Monday, Jul 25, 2005 at 19:27

Monday, Jul 25, 2005 at 19:27
Ray
Have run 8mm cables from car to caravan via 50amp anderson plug to two 40amp gel batteries in parallel. Have solidnoid in car for cable when engine is running only.
Have solidnoid in caravan to isolate battery charging if needed to. Use caravan fridge on 12volt during day when travelling. I do not leave car charging all day when travelling let (Electrolux) fridge run on battery only for about two hrs then charge for about same. Been using this set up for about four years. Travelled to west every year from Kimba SA. In January and October mainly. Never had problem with 8mm cable. First trip only had 4mm cable and did not work, nearly wrecked batteries.

used same setup with camper trailer to central aust last year but with sealed lead acid battery and charging all time vehicle engine running with no problems. (Engle Fridge)
Cheers
Charlie
AnswerID: 121982

Reply By: gbz2 - Monday, Jul 25, 2005 at 20:25

Monday, Jul 25, 2005 at 20:25
just interested in when hooking up your camper back to main vechile how long it would be before the camper battery starts to drain the main vechiles battery to a level where you wouldnt be able to start main vechile. assumming you havent got an automatic solonoid.
AnswerID: 121996

Reply By: angler - Monday, Jul 25, 2005 at 21:09

Monday, Jul 25, 2005 at 21:09
If your ct has an absorbtion type fridge, electrolix or dometic then the battery drain is around 15 amps just for the fridge. I use a charger setup on an inverter, If you know a sparky he can put a capacitor across the 240V output and this will increase the 12V output due to power factor improvement. The inverter does not have to be sine wave in this situation. Charging from the car even with large cables will not work really well if you have one of those power hungry fridges. It works with an engel or waeco OK.
AnswerID: 122010

Reply By: fourplayfull - Monday, Jul 25, 2005 at 22:47

Monday, Jul 25, 2005 at 22:47
No , just direct hook up to aux. with a simple redarc iso between engine batt which is also AGM .
If one battery say aux. has a higher charge than the other 2 , the alt. decreases charge rate thus extending recharge time - thus the reason to keep the use even on all batts .
When ct left at campsite while you go "4bing" for the day the aux. will be at a higher charge than the ct so on return, connect andersons to allow the batts to equalise overnight .
I forgot to mention earlier , the 4by has a 60 litre engel running as well .
As back up , which has not been needed yet , I have a Yamaha 1000 inverter gen set powering a 3 stage 40 amp True charge batt charger hard wired .
Remember inverters loose approx.20% - you cannot get 240v out of 12v for free .
CYA John
AnswerID: 122027

Reply By: neilvin - Tuesday, Jul 26, 2005 at 11:21

Tuesday, Jul 26, 2005 at 11:21
Use an Arrid Twin Charge from the 12v shop as Dodger suggested
They work fine
Neil
AnswerID: 122088

Reply By: Member - Collyn R (WA) - Wednesday, Jul 27, 2005 at 11:55

Wednesday, Jul 27, 2005 at 11:55
It is possible that the current interest in inverter/three-stage battery charger setups follows my Tech Notes article that was published The Wanderer (the CMCA's monthly journal) some half year ago. I have also described and suggested it on several Forums.

It is primarily of benefit in motorhomes that have 24-volt vehicle electrics and 12-volt house electrics, but is well worth considering otherwise.

Before eloborating, I'd like to comment on a number of issues raised in this thread.

That conventional lead acid batteries rarely charge beyond 70% in vehicles is not a myth. Whilst is true that 13.8 volts will eventually bring a battery close to full charge the time required is virtually weeks. Several battery makers state that caravan batteries are typically unlikely to exceed 65%.

The 70% voltage limitation is deliberate as it safeguards batteries against overcharging on very long trips or non-stop usage. Starting is not compromised as the system is designed accordingly.

In practice (as opposed to theory) most car batteries do charge to approx 70%. They discharge to about 67.5% whilst starting. Because they fall to below 9 so volts whilst doing so (and there is thus a huge diffetential between battery and alternator voltage), the energy used is typically replaced by the alternator within a one-two minutes. Whilst the charging limitationm does not affect starting, any parallel charged battery has the same limitation forced upon it.

Most conventional paralleling charging methods work reasonably well but are usually a compromise if disparate batteries are involved - as their charge acceptance characteristics are almost certainly different. Rotronics up-market device gets around this - but is very costly.

The inverter/charging system is most economic where an inverter and/or mains battery charger is needed anyway, but is worth considering generally.

It advantage is that no modifications need to be made to the vehicle (the inverter is just another appliance) and that the charger can be set to provide the optimum charging regime for the battery.

It needs neither humungous inverters or heavy cabling. The charger needs not be huge as long as it is a three-stage unit that provides constant current charging.

Charging a battery at (say) a constant 20 amps is far better than most alternator/regulators can do - so a 20-25 amp charger is adequate unless you have a heap of battery capacity. Driving the charger requires (at most) a 500-watt inverter, connected by cables capable of carrying about 27.5 amps.

I have one minor reservation re using this technique with a trailer. And that is the legality of running a low voltage (240-volts ac) cable between towing vehicle and trailer. There appears to be nothing in AS/NZS 3000:2000 or 30001:2001 that covers this. Whilst I am a professional engineer with electrical engineering experience I am not a licensed electrician - and those I have discussed this with are as equally unclear.

I have no hesitation in suggesting it otherwise. An increasing number of motorhome owners are using it with every success.

I will arrange to post the CMCA feature on my own website asap.
Collyn Rivers
AnswerID: 122266

Follow Up By: Ray Bates - Wednesday, Jul 27, 2005 at 19:38

Wednesday, Jul 27, 2005 at 19:38
Dear Collyn,
It would appear that you are thinking on the same lines as me regarding the inverter/charger system. My DSB is mounted in a rather large metal box on the drawbar of my caravan and has adequate spare space for an inverter and a charger. I would though not consider running 240V all the way from the car and all the conversion would be done in this box. I already have a 150watt inverter but my charger only gives out 15amps which according to your calculations is not sufficient. I already have 18mm2 (4Australian Standard Wire Gauge) running from the car to the caravan so voltage drop should not be a problem. The toolbox is seeled and lockable and the length of 240v cable would be very short and nontouchable except for maintenance.
Thank you for your comments
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FollowupID: 377539

Follow Up By: drivesafe - Thursday, Jul 28, 2005 at 18:31

Thursday, Jul 28, 2005 at 18:31
Hi Ray, with the size of cable you already have, I would lay money that if you tested the two ways of charging your rear battery that you would not only charge the battery quicker by simply connecting the cable straight to the battery, you would ultimately use far less power and as such reduce wear on you alternator.

Using the inverter/charger set up will work but will take longer, require far more power compered to the amount of power you end up storing and as stated, you are just making your alternator work harder for no advantage over a conventional system. The inverter/charger set up is just overkill with no real gain.

One more point, some motor homes may use the Inverter/charger set but I supply auxiliary battery charging gear to a number of automotive companies, including Australia’s largest motor home manufacture and I can assure you, even with the huge inverters and battery chargers that these vehicles come with, nothing charges the banks of batteries that some of the vehicles have, quicker than the voltage coming directly from the alternator.

Cheers
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FollowupID: 377762

Follow Up By: drivesafe - Thursday, Jul 28, 2005 at 19:27

Thursday, Jul 28, 2005 at 19:27
Ray here is suggestion for you.

If you really want to use the Inverter/charger set but want to get the quickest charge then when you know you are going to be doing a fair few hours driving.

For the first two or three hours ( depending on how discharged the battery is ) run the cable straight to the battery then after that connect up the Inverter/charger.

You will get the bulk of you charge at any time in the first few hours and doing it this way will also continue the charge at a high voltage off the charger.

Still, unless you have an inverter and charger already, installing an additional battery in the van would be far more efficient and cost effective set up.

Cheers.
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FollowupID: 377770

Reply By: Member - Collyn R (WA) - Thursday, Jul 28, 2005 at 14:46

Thursday, Jul 28, 2005 at 14:46
Ray

It sounds great - particularly the 18 sq mm cable!

Incidentally that is the approach I suggest for people with fifth wheelers (ie running the final metre or two at 12 volts).
Collyn Rivers
AnswerID: 122554

Reply By: Member - Collyn R (WA) - Friday, Jul 29, 2005 at 17:03

Friday, Jul 29, 2005 at 17:03
Nick

AGMs have very low internal impedance. This provides their happy characteristic of charging quickly and very close to 100% from much lower charging voltages than are needed for (particularly) deep-cycle batteries. They will accept voltage between 13.8 and 14.6 or so.

Their operational voltages are also a tad higher than conventional batteries.

In my new book (The Camper Trailer Book) that I am just about to print, I quote off-load rested voltages as 100% charge - 12.8 volts, 75% charge 12.6 volts, and 50% charge as 12.3 volts (ie all about 0.1 volt higher).

As AGMs reduce in price I believe increasingly they are the way to go.

Re having all AGMs or no AGMs, I am partially responsible for this belief having stated this in many magazine articles and in early editions of my books. I did so because that's what their makers warned.

Since then however, Redarc and other similar voltage sensing relays have gained wide acceptance. As long as one of these delays paralleling until the starter battery reaches about 13.6 or so volts, there seem no major problems in parallel charging and thousands of people now do so.

One further reservation is that the charge acceptance is such that there may be a risk of overloading an alternator if attempting to charge too large an AGM battery bank.

There is next to no risk of charging an AGM at too high a rate - they will withstand substantial input currents.
Trust this helps
Collyn Rivers
AnswerID: 122738

Reply By: Nick - Friday, Jul 29, 2005 at 18:52

Friday, Jul 29, 2005 at 18:52
Collyn

Thanks for clarifying that.

I have searched for and found many comparison charts of rested voltage vs. charge % and they seem to vary quite a bit. I was never sure which one to use. Yours seems on the pessimistic side, but you may well be right. It is never easy to know the true AGM battery charge status because of all the variables which affect the voltage reading. It is especially difficult to know what’s going on when you are actually using the auxiliary battery as you don’t get the chance to rest it. I haven’t been able to find any “rules of thumb”, however inaccurate, to help interpret the state of charge voltage readings you get while say a 3 amp fridge is drawing power at the same time. Do you have any comments, or do I keep wondering what the readings really mean?

Thanks
Nick
AnswerID: 122752

Follow Up By: Member - Collyn R (WA) - Saturday, Jul 30, 2005 at 09:11

Saturday, Jul 30, 2005 at 09:11
Nick
It's not really a pessimistic approach - for any given percentage charge, an AGM battery's output is typically 0.1 -01.5 volt higher than most. This is due to its lower internal impedance. I'd be more inclined to see this as a plus because whatever you are driving via anm AGM will be fed with a marginally higher operating voltage at any given state of charge.

It is close to impossible to obtain reliable indications of battery charge from instantaneous voltage (or even hydrometer)measurements. This is because of the very long electrochemical reactions within the battery.

Because of this a still almost totally discharged deep-cycle battery present as fully charged for some time after being given a short heavy current charge - and a close to fully-charged battery may present as close to flat for some time after driving (say) a microwave oven.

Further, the battery's internal impedance introduces a voltage drop related to the external current drawn. Thus drawing any current from a battery will drop the voltage across it, but by just how much depends on the internal impedance, temperature, state of charge and Ah capacity (ie it's a nest of worms!). Abou all one can assume is that the actual battery voltage will always be higher than shown on a voltmeter whilst that battery is under load - and will generally be much higher for a deep-cycle battery than for a starter battery or AGM.

The only reliable way is as we keep track of money. Count what comes in, count what goes out (allowing for any losses). What's left is what you've got.

With batteries, this is done by energy monitors - and that function (plus many others) is built in to most up market solar regulators.

There really is no other reliable way - all other methods have huge potential errors and equally huge potential to mislead. I have seen many otherwise perfectly healthy batteries discarded through this.
Trust this helps
Collyn Rivers

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FollowupID: 378013

Follow Up By: Nick - Saturday, Jul 30, 2005 at 10:34

Saturday, Jul 30, 2005 at 10:34
Collyn

Yes, pessimistic was the wrong word, I meant pessimistic from the viewpoint of someone checking his battery's voltage against a %charge estimate and wishing he had more charge left than he has!

Thanks for the other info. I might conduct a few experiments to see what-happens-when with load applied for a while and then disconnected and rested.

Nick
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FollowupID: 378023

Reply By: Mainey (WA) - Sunday, Jul 31, 2005 at 22:58

Sunday, Jul 31, 2005 at 22:58
My opinion on charging aux batteries is simple and based on some experience;

Use the largest Deep Cycle battery bank you can fit in a given area

Use Large cable to the aux batteries, both pos and neg leads

Use solar panel/s with a good solar regulator

Reason is;
solar works when you are not driving
solar gives high voltage

yes, is only my opinion :-)
AnswerID: 123079

Reply By: Ray Bates - Tuesday, Aug 02, 2005 at 20:41

Tuesday, Aug 02, 2005 at 20:41
Hi,
When I first asked the question I did not know that it would cause so much contaversy. Sorry if I have cause any of you any trouble
AnswerID: 123441

Follow Up By: drivesafe - Tuesday, Aug 02, 2005 at 21:30

Tuesday, Aug 02, 2005 at 21:30
Ray, you have nothing to be sorry for, if anything, I owe you an apology for continuing to debate with Collyn R.

As stated above, one of the main advantages of sites like this is that anybody can post a question and hopefully get an answer or even a number of answers and then you can go off and use this newly gained info to your advantage.

Don’t ever worry about asking a question of any form, it’s your right.

Cheers
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FollowupID: 378479

Follow Up By: Member - Collyn R (WA) - Wednesday, Aug 03, 2005 at 18:16

Wednesday, Aug 03, 2005 at 18:16
Ray
It does not seem feasible to continue to discuss this issue publicaly. If you wish I'm perfectly happy to reply to you privately. No need to apologise, the result was not remotely of your making, but I thank you for your courtesy in doing so.
Collyn Rivers


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FollowupID: 378645

Reply By: drivesafe - Monday, Aug 08, 2005 at 15:30

Monday, Aug 08, 2005 at 15:30
For the benefit of anybody considering using the inverter/charger set up, you may be interested to know that this has been done but is considered by Workcover in NSW as an unsuitable work practice and have apparently notified a number of organisations informing them of their displeasure relating to this form of operation.

Note this specifically relates to work place operations but there must be some question to the safety of the sort of operation.

Cheers
AnswerID: 124294

Reply By: flappa - Monday, Aug 08, 2005 at 15:51

Monday, Aug 08, 2005 at 15:51
Ray , what you have discovered is 12v systems are a HUGE topic of debate (like Hiclones , Nissan V Yota etc etc).

Ask a question and get 100 different ideas , some right , some wrong , some that WILL work , but not necessarily , the best way etc etc.
AnswerID: 124298

Reply By: Mike DiD - Sunday, Aug 14, 2005 at 10:03

Sunday, Aug 14, 2005 at 10:03
It isn’t easy to find information on using battery voltage DURING DISCHARGE to indicate remaining charge, but here is a compilation of what I’ve found. As you can see from the Open-circuit voltages on the left from various sources and battery types, there is quite some variation for battery types.

0x 0y 0z 0w 3 4.5 22 90 270 340 Amps
100% 12.70 12.66 12.80 12.80 12.5 12.8 12.5 12.2 11.6 10.4
80% 12.42 12.49 12.64 12.55 10.2
60% 12.20 12.32 12.48 12.30 9.9
50% 12.06 12.24 12.40 12.18 12.4 12.2 12.0 11.8 11.3 9.4
40% 11.90 12.16 12.32 12.06 9.5
20% 11.58 12.06 11.96 11.82 8.9
0% 10.50 11.89 11.80 11.60 10.6 10.8 10.4 9.5 9.4 6.0

Sources

0x - unspecified battery www.windsun.com/Batteries/Battery_FAQ.htm#AGM,%20or%20Absorbed%20Glass%20Mat%20Batteries

0y - Low Maintenance (Calcium Lead) Battery - www.uuhome.de/william.darden/carfaq4.htm
unspecified battery http://www.batteryuniversity.com/partone-13.htm and www.ibsa.com/www_2001/content/faqs/tech_talk/maintenance/faq_tech_maint.htm

0z - Maintenance Free (Calcium-Calcium) or VRLA (AGM) - www.uuhome.de/william.darden/carfaq4.htm

0w - Odyssey Staring Battery Handbook.

4.5A to 270Amp - Absorbed Power N70-size 90AHr AGM deep cycle battery - http://www.absorbedpower.com/battery/pdf/AP-GT12-90C-01Sep05.pdf

3A and 340A - 60 AHr unspecified battery - www.cyb.com.au/automotive/batt_facts/undbatt_2.htm
AnswerID: 125081

Reply By: Patrick - Sunday, Aug 14, 2005 at 11:22

Sunday, Aug 14, 2005 at 11:22
What an intertesting thread. I find these type of non-agressive deabates very thought provoking. I have been reviewing battery use on my own van and have found the many points raised here full of information.

Great input from all.....thank you
AnswerID: 125090

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