What size auxilary battery do I need?

[goldrush]

Can anyone tell me how to choose what size battery i would need to run various accessories ? If I know the power used by these things in watts how do I figure out how many amp/hrs I would need from a battery ?

[BUSHNUT]

Hi Goldrush,

There are 2 things I dont stuff around with and thats brakes and electrical, a reputable auto eloectrician is the best to answer your question. My auxillary battery is one of these 50% cranking, 50% deepcycle battery,not totally convinced as yet about it, there is some favourable reports about these new calcium batterys, but I tend to wait and see if they are as good as they are cracked up to be, the secret to any dual battery system is a reliable isolater switch system.

Another thing that is overlooked is the capacity/performance of the alternater to recharge, you can have the greatest battery under the sun but if your alternater is not up to scratch then its all for nothing.

As I am a diabetic, refrigeration is very important for insulin,not forgetting the beer and other goodies, I run 2 fridges a 40 and a 32 litre Engels, depends on who I am going away with as to which one holds the grog.

If it is what I call a rolling camp - where you up stakes and move on to the next destination each day then with an alternator performing as it should you should be okay .

With standing camps - where you sit and prop for a few days, I carry a 80 watt solar panel to keep the battery up to it, I also carry an Engel pack as back up just in case- cant let the grog get warm.

Remember that with an alternater that is up to scratch you need to run your motor at least 1000 rpm for at least 40 minutes each day to keep the battery up to the mark.

A couple of members are probably a bit more informed about this Tectrek for one.

A lot of the new so called sookie la la fourbie batterys are not designed to do anything streneous, two discoveries on our trip across the Simpson Desert had problems just running a fridge - a winch was out of the question.

Safe Travel

Bushnut

[ZORDO]

Mate i just use the two biggest batteries that i can fit. you can never have too much battery power.
Cheers

[centaur]

Originally Posted by ZORDO

Mate i just the two biggest batteries that i can fit. you can never have too much battery power.
Cheers

I agree, I have just had fitted a Calcium 730 CCA Battery as the starter battery, and a Normal 630 CCA as the Aux battery using a Redarc Smart Solenoid. I then changed things like spotlights relay, UHF, air horns etc to run of the Aux battery. The UHF has a switch that I can choose between switched power or Aux battery.Went camping on Easter long weekend, and had the stereo/UHF running all weekend, with pumps for the kids air beds, and lights, without a drama.

It would be wise, especially if powering items during a camp, to get the biggest, best batteries you can afford. I chose the calcium battery due the high power output of these batteries, but I am waiting to see how they are when they are deep cycled!

Anyone else got any info on the CValcium Batteries.

[tektrek]

Originally Posted by goldrush

Can anyone tell me how to choose what size battery i would need to run various accessories ? If I know the power used by these things in watts how do I figure out how many amp/hrs I would need from a battery ?

G'day Goldrush.

I am asked this question at least 4 times a week and it is not easily answered in a few words but here goes.

To find out how many amp/hours (Ah) you need, convert the watts by dividing them by 12 which will give you the ampere current (A) rating for each appliance. Next estimate the amount of time in hours consumed by each appliance like say 6 hours for a 1 amp camp light (ie Versalite) and so on. When you have a total figure of amps used per 24 hours, divide that the number into the Ah rating of a deep cycle battery (Calcium, Calcium Lead, AGM, Gelled Electrolyte etc). Most people fit 80Ah to 100Ah deep cycle batteries in their 4WDs as this size fits most auxiliary battery trays. 12v inverters can be calculated by dividing their watts by 10 to give amps, 24v systems are divided by 20.

Points to consider -
1. Do not use an engine start battery as it is not designed for deep cycle applications, only engine starting. Start batteries are only rated in CCA, never in Ah. They are designed to give huge amounts of current in a few seconds which is consumed by starter motors. A deep cycle battery on the otherhand is designed to give constant power over a long time period. Typical deep cycle battery rating is 12v @ 80Ah @ C20 discharge rate.

2. Do not discharge the battery by more than 80% capacity if you want more than 2 years life. Typical deep cycle battery life at 50% discharge is usually around 8-10 years.

3. Use a battery isolator to separate the two batteries to prevent backflow equalisation. Start batteries normally sit around 12.5-12.7v and deep cycles at 12.8-13.0v. If left connected they will try to equalise each other thus resulting in the early death of either or both through sulphation. I use a bilateral isolator myself which means that I can connect a charge source to either battery and charge both at once. After charging i automatically get isolation.

4. Use multi stranded cables for all connections and keep them short where possible to reduce voltage drop. Get cable like OFC monster cable from Jaycay or Dick Smith as it has a very low volt drop. We use this stuff as a cheap alternative to rather expensive solar low loss cable for long runs.

5. If you are base camping for a few days it would be wise to invest in a solar panel to keep up the charge to the deep cycle battery. If you are interested in this concept, email me and I will do a deal for you.

Hopefully the above will give you a bit of a lead to solving your question but should you need help please feel free to email me tektrek@optusnet.com.au and I will assist you further. By the way I am a battery, battery charger and solar power dealer and can give you and any other member of this forum a good price on any of my products. Some of my products can be seen at www.tektrek.com.au

[centaur]

Originally Posted by tektrek

G'day Goldrush.

I am asked this question at least 4 times a week and it is not easily answered in a few words but here goes.

By the way I am a battery, battery charger and solar power dealer and can give you and any other member of this forum a good price on any of my products. Some of my products can be seen at www.tektrek.com.au

Very informative post, and one I read with great interest. I have also just visited your site,a nd I am now going to hassle my missus for the Credit card....

Just a quick question, you list on your site the "The Voltage Sensitive Relay", as a simple and cost effective unit. This is probably going to be a dumb question, but how does this unit compare with the Redarc Smart Solenoid that I have just had fitted to my Landcruiser? I had done a fair bit of research and asked a few Autro Ekecs, and the consensus was to use of the these units, which is what I have done!

Does your unit carry out the same tasks, have similiar features or even better features? I am concerned now that maybe I have not chosen wisely. I have only owned a 4x4 for less than a year, and with 7 kids, takes me a long time to save for this equiopment and would hate to think I have made an incorrect choice.

I am interested in your reply.

[tektrek]

Hi Centaur,

Unfortunately there are very few if any auto elecs that know about the Voltage Sensitive Relay as it was designed for marine applications like cruisers, yachts and especially trawlers.

The Redarc isolator is known by most 4Wders and auto elecs due to agressive advertising which your research has indicated. BEP Marine in NZ (the manufacturer of VSR) has done likewise in the marine industry worldwide.

We discovered a few years ago that the VSR could be used with 4WDs and at a price below that of other isolators like Redarc. The VSR we sell compares favourably with the Redarc unit (they both work on the same voltage sensing principle) with the exception that ours is completely watertight, simpler and faster to install. Our isolator can be installed by the average handyman whereas the Redarc unit usually requires an auto elec for installation which adds to the overall cost. Unfortunately the Redarc unit is not totally watertight (Redarc instruction sheet states "Spraying the unit with a good grade silicone sealant at installation will assist to ensure total protection".) which means you need to be careful with high pressure water cleaners and ensure that it is well protected from river crossings and deep bogholes. Our isolator will easily cope with lots of water around and will according to the manufacturer, even work in a bucket of water without any water ingress to the electronics.

You have not wasted your money in buying a unit that in most respects works well. The VSR we sell is somewhat better in environmental specification, ease of installation, and price. By the way, the VSR can easily be used between an auxiliary battery and a caravan battery too which puts an automatic end to having to remember to manually disconnect any plugs on the towbar when stopped.

I hope the above helps.

- tektrek

[goldrush]

Thanks tektrek. Your info is exactly what I was looking for. When the finances ( and SWMBO ) allow I will give you a call about supplying all the gear I need for my rig.

[tektrek]

Originally Posted by goldrush

Thanks tektrek. Your info is exactly what I was looking for. When the finances ( and SWMBO ) allow I will give you a call about supplying all the gear I need for my rig.

It's a pleasure and thank you.

[centaur]

Originally Posted by tektrek

Hi Centaur,

You have not wasted your money in buying a unit that in most respects works well. The VSR we sell is somewhat better in environmental specification, ease of installation, and price. By the way, the VSR can easily be used between an auxiliary battery and a caravan battery too which puts an automatic end to having to remember to manually disconnect any plugs on the towbar when stopped.

I hope the above helps.

- tektrek

Thanks for your reply, good to know that I have not been led up the garden path. When you say it works well in most cases, I gather that just means the weather/waterproffing, or is there other areas that my unit fall sdown in when compared to yours.

Just asking, my friends are thinking of going down the same path, and I wouldlike to be able to give different advise or a comparison between my gadget and yours. Thanks.