second battery for 60Ltr engel ?

sorry bout that !! im from adelaide

Hi Mainey, I want to buy two batteries for my camper after Christmas. I live in Newcastle I am looking at spending around $600.00. I already have a 120amp hour AGM that I got from TJM not sure of the brand in the rear of the vehicle.

We are basically running a 60litre engel and 12 volt lights. We have a solar panel as well so I am thinking the extra batteries should see me have enough power given the most we usually stop in one place without power is 5 days.

Thanks and sorry to hijack the thread....I guess I should think about becoming a member so I can send direct :)

mazda bravo 2.6petrol 1995 dualcab,305,000kms, hehe, redarc 100 amp isolator, battery in back tray 5m of 13mm2 cable to the back, 3days without driving car at most and not on the dole but soon could be!!. would like to spend no more than $250 on battery if possible.only running fridge and it has a new compressor in it so running 4.5amp
darren

Hi Darren,
That's something to get the teeth into, first thing that jumps out. Your cable is way too small, far too much voltage drop to have a chance of fully charging the battery in the tray.

This image is a screen grab of a spreadsheet I made up some time back to calculate whether a given cable size is suitable for a given load. In this scenario I've assumed the Bravo has an 80 Amp alternator. Using 13mm2 cable you are losing over 1 volt or 8.3% odd of your charge in the cable alone! (I've also assumed a 5 metre positive and 5 metre negative cable = 10 metre circuit)

Let me know if any of those assumptions are incorrect.



Now, on to your battery.

If we use your number of 4.5Amp and guess that the Engel will run for say 8 hours a day then you'll be pulling 40Ahrs in a 24 hour period. Note: 4.5Amps x 8 hours does equal 36, I added 10% for losses and fudge factor.

So to get three days you'll need 3 x 40 = 120Ahrs of useable power. If we assume a battery charged to 100% of its stated capacity is spent at 50% charged then we need to double that to 240Ahrs!

I don't think you are going to get a 240Ahr battery for $250 unless it gently falls off the back of a truck!

You'll need to carefully monitor the voltage and charge a battery around the 100 - 120Ahr more frequently is my guess. A sealed lead acid Deep Cycle will give you the lowest entry price but will require you keep it well charged and don't let it go below that magic 50% for long perids. (days) You'll have to fix that voltage drop or it won't recharge successfully and it will sulphate and die.

Or look at a supplementary solar array for when you are stationary for longer periods.

I have two 105Ahr AGM's in my troopy running my 110 litre Waeco and get about 2 days if all goes well and the weather isn't real hot. The vehicle was sealed up all weekend last and the fridge had stopped on low voltage around the 36 hour mark. At the moment my only charging method for them is a 25Amp 3-Stage charger so I can pretty safely say they are always returned to 100% when charged.

Hope all this helps,

Geoff

Is the effect of the voltage drop a bigger or smaller issue if the battery is mounted in the boot rather than in the engine bay?

Basic rule of thumb, the longer the wire the bigger it has to be to combat voltage drop if the volts and amps are constant.

The boot is a long way form the alternator, you'll get more voltage drop.

Geoff

What would the approximate circuit length be if the cable were to run from the alternator to the boot in a standard stationwagon car? You've allowed for 10m in your spreadsheet which sounds like a lot to me, or are you also counting the cabling that goes from the battery to the auxilary equipment?

I allowed 10 metres which is made up of 5 metres for the positive wire and 5 metres for the negative wire.

The cabling from the battery to the other equipment is entirely seperate.

Geoff

Oh, and to answer your original question, I reckon you can't go past AGM batteries. A bit more expensive, but worth the money in my view. The cheaper brands (made in China) like Fullriver, Remco etc) are good quality and excellent value for money.

Norm C

Hi Norm,
I think you are right, I did size for worst possible case!

It's easiest in electrical design to assume the worst when only limited information is available then work back from there!

Geoff

Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies.

I can relate to that......but I also get baldness watching the Knights.....lol

Hey Marc,
Whereabouts in Newcastle are you?

I'm currently at Shortland.

Geoff

Hey Geoff, just a stone's throw away mate. I am at Waratah West not far from the uni.

Keep an eye out for the white Troopy with the ExploreOz wheel cover!

Geoff

Will do. I am in a Series 2 TD5 Disco....southern cross sticker on the left side window....

Where is the best place around newcastle to go for batteries?

Hi Marc,
Give it an hour or so then flick me an email on,

contact_geoff@internode.on.net

Once we make contact on that I'll delete it to annoy the spammers and use my regular email address.

Save driving poor Norm nuts and getting rightly moderated.

Geoff

Geoff, that email address bounced back to me?

Have a crack now, I just sent an email to mysefl and it worked.

Geoff posted the worst scenario and Norm C Posted his proven experience with doing the job.

Both are in a way correct correct as the worst scenario covers maximum and can never be a problem.

Alternators are cold rated and the continuous duty would be around 60% so in reality you can work on cable sizing for that load as the alt will only produce maximum output for a short period.

Once the initial cranking battery has recovered from starting the vehicle which is normally only a few minutes the regulator cuts back the charge rate and you may only get a charge that would be covered by Norms sizing of the cable and definately suitable for that purpose.

Most people do not understand voltage drop in DC and have a tendency to underwire everthing and think they are working OK when they are not.

It is better to overcable to be sure than undercable and be sorry.

Ian

Norm C , have you checked out the price of what WAS the cheaper brands of AGM lately ?? Fullriver + Remco can now not be called cheap or entry level anymore , Same size batt that was $200 5yrs ago is now close to $500.

Whitworths recently had 100 AH Remco AGM for $339. Bias Boating have AGMs (Remco or Amp Tech not sure which as they have pics of both in the catelogue) - 100 AH $369, 120 AH $399.

Price of lead pushed battery prices way up over past couple of years. Lead is now much cheaper, but so is the Aussie $ unfortunately.

Norm C

i only have 5metre cable on the positive side and grounded on negative.