Advice on duel battery setup.

Submitted: Thursday, May 20, 2010 at 18:26
ThreadID: 78617 Views:3097 Replies:4 FollowUps:0
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Hi Guys,

I have recently bought a van which I am looking to customise and add a second battery to in order to run some electrical equipment. At this stage, I'm just looking into what would be a suitable setup. I am yet to buy most of the equipment so would appreciate any input and recommendations. This is a bit of a project for me so I'm prepared to spend quite a bit of money on it so rather than opting to buy what is within my budget, I'd rather find out what would be the best option and then save money to buy it.

The items which I would be requiring power for would be:
- a fridge (probably a waeco cf-50L)
- roof mounted dvd player
- a few lights
- a stereo
- charger for phone, camera, laptop (I have a 250W inverter though am considering buying DC chargers)
- possible UHF or HF radio in the future.

I have read quite a few articles on this site but my electrical knowledge is minimal. I am learning towards the idea of a AGM deep cycle battery, as in my van the battery is under the drivers seat and there is not a lot of room for a second. So with an AGM battery I could find another position in the back of the van to mount it.To allow for future expansion, I figure I would rather pay extra to get a larger battery, maybe 200-250aH.

If I choose a larger battery, as opposed to a 100aH, would it recharge at the same rate?
For instance, if I use 60aH of power overnight of a 200aH AGM battery, will this be recharged at the same rate as if I used 60aH from a 100aH AGM battery?
If I'm driving for say 3 or 4 hours the next day, will that be sufficient time to recharge the 60aH I have used the previous night?

At some point in the future I would also like to add a couple of solar panels to recharge the AGM battery on trips where I'll be in one spot for a few days. Will it be difficult to incorporate it into the setup?

Due to insufficient electrical know-how, I will be paying to have it all installed so just need to buy the parts.

I realise I need:
- AGM Deep cycle battery 200aH (any suggested brand? I hear fullriver are supposed to be good)
- an Isolator (Redac?)
- spike / surge protector (if not built into the isalotor)
- battery monitor
- and I pressume the electrician will have the required cabling (100 amp 8 B&S?)

Is there anything else I will need? or any electricians in Perth worth a special mention for the job?

Any input is appeciated. Thanks
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Reply By: Maîneÿ . . .- Thursday, May 20, 2010 at 19:15

Thursday, May 20, 2010 at 19:15
Fullriver are not as expensive as most other batteries, that’s possibly why you hear about them more often.
Most times the question is related to 'where can I buy a battery and also save money too'

You can't save money buying expensive batteries *initially* but in the long term you will realize the benefit of a quality battery over an inexpensive one is not only in price.

If an electrician offers you 8 B&S cable look for a new electrician, use 2B&S.

Why not consider an electronic battery isolator over a mechanical solenoid?

Maîneÿ . . .
AnswerID: 417417

Reply By: ChipPunk - Thursday, May 20, 2010 at 19:17

Thursday, May 20, 2010 at 19:17
"If I choose a larger battery, as opposed to a 100aH, would it recharge at the same rate? "

No, but the answer I think you are after is yes.

The same amount of energy/power is taken from both batteries so the same energy has to be replaced. That's the simple part....

The bigger battery will have "discharged less" wrt its capacity - ie, it will be at a higher voltage and has more in reserve.
Because it is at higher voltage, it may recharge at a lower rate, but being bigger (and a higher voltage) it probably has a lower internal resistance so recharges quicker.....

The main consideration is the bigger the battery, the better it will handle a given drain - the longer it will last etc.
And that's where practicality and cost comes in....

I realise that you & others herein are not electrically minded, however I add the following regarding a simple & cheap battery isolator for consideration.
Any auto electrician should be capable of implementing the following and assessing its applicability (ie, newer ECU controlled alternators), but feel free to stop here and stick toRedarc or other isolators as recommended by others.

I prefer and use a relay that is controlled by the charge lamp circuit.
A 140A relay costs ~$15, and 200A-400A about $25.
Add a 20c diode and they provide the same spike protection as the Radarc.

I see no advantage to Redarcs and other similar voltage sensing isolators other than one less connection, and its over-voltage protection (but only for the secondary switched circuit) and that they only connect when above a certain voltage.
But the latter can be a disadvantage, and requires timing circuits/delays to avoid certain situations.

OTOH, the charge lamp method connects the other batteries only after the vehicle has started ad the alternator thinks it is "charging".
It's cheap and without the "smart" complexity (your alternator's regulaor provides that), and can uses virtually any relay and can be extended to any capacity.
It does require ONE extra wire - namely that to the alternator's charge-Lamp circuit, but otherwise it is identical to Redarc and other isolator cabling (except for diode isolaters - and I would rarely recommend those for high-current and vehicle applications!).

I do however describe a solution for DIY and self-sufficiency with maximum redundancy, reliability & adaptability; with minimal costs using "standard" components.
With that, most users will have a voltmeter else alarm that monitors battery voltage (so they know the exact state of their system).
Things like alternator over-voltage are covered by primary systems (not secondary as with the Redarc).
And with a voltmeter, collapsed batteries etc should be evident.
AnswerID: 417418

Reply By: Member - John and Val - Thursday, May 20, 2010 at 20:17

Thursday, May 20, 2010 at 20:17

With the battery some distance from the alternator, fully charging it becomes an issue. If you are going to instal a 200 Ah battery, I'd suggest look into a 30A dc-dc charger such as is available from ABR Sidewinder (a commercial member of this forum). This will ensure that the battery gets a decent charge from the alternator, will increase the available voltage and overcome voltage drop in the cabling. Cables should be substantial, as you are already aware.

I use something similar to ChipPunk's switching system, much less expensive than other controllers and totally reliable.

You may get some extra ideas from our blog Electricity for Camping .

Your energy budget, allowing 60 Ah overnight, sounds a bit high. I budget on about 35 - 40 Ah per 24 hours, with simial loads to those you propose. If you fit a 30 Amp dc-dc charger, it should actually deliver 30 amps, completely replacing within a couple of hours the energy you've consumed in a day.

Charging time? As suggested above, the time to replace the energy you've used will be roughly the same, regardless of the size of the battery. To fully charge your battery though a dc-dc charger would be a great advantage.

Finally, you are probably aware - when fitting a battery inside the vehicle it should not be a wet acid type. AGM or gel are more expensive, but much safer.


J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein

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AnswerID: 417430

Reply By: LindsayC - Friday, May 21, 2010 at 19:51

Friday, May 21, 2010 at 19:51
Call into your nearst BATTERY WORLD store they stock the new CTEK dc-dc charger. A geat way to charge your batteries quickly and to there full capacity
AnswerID: 417583

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