Can you have too many batteries?

Submitted: Sunday, Feb 06, 2005 at 10:06
ThreadID: 20166 Views:3344 Replies:8 FollowUps:10
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Have a Patrol GU, also have a Jumbuck Camper.

I'm looking to put a Dual battery system in the Patrol, and the Jumbuck already has a small cranking battery in it but it is on the way out.

I've been told not to bother with Deep Cycle batteries and I would be better to buy in two more cranking batteries same size OR LARGER than my starting battery

Supercharge Gold MF MF95D31L 720CCA 160AH $130

I'd run some 6-8mm cable down to the camper to charge that battery, I'd throw some heavy duty isolator switchs inbetween the start battery and the other the alternator in the Patrols are rated at 90 amps, If I run the 2nd battery and the camper trailer battery down and partially drain the cranking battery could the alternator cope with load of charging all three batteries?

Should I look at putting a deep cycle in the camper? Only reason I hesitant about Deep cycle is you never get them back to 100% charge when out the middle of nowhere as the require 15-16Volts to charge up to 100%. Alternators only output 14.8 which satisfys the thirst of cranking batteries to get them to 100%.


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Reply By: Scubaroo - Sunday, Feb 06, 2005 at 11:36

Sunday, Feb 06, 2005 at 11:36
Have a look into AGM deep cycle batteries - they seem to get around most of the charging issues.
AnswerID: 96923

Reply By: Member - Jeff M (WA) - Sunday, Feb 06, 2005 at 11:52

Sunday, Feb 06, 2005 at 11:52
Charging a 160A/H battery with 6 or 8mm cable?? Am I the only one concerned about this? Personally I'd be using 8g minimum to charge a battery.
AnswerID: 96926

Follow Up By: Member - JohnR (Vic) - Sunday, Feb 06, 2005 at 13:19

Sunday, Feb 06, 2005 at 13:19
Agree with you Jeff, that is why the comment above about never being able to charge the batteries was made in the original comment. Seldom do people realise the voltage drop across 6mm and even 8mm cables make it a surity.

Just threaded a house supply cable through a land cruiser recenly, in conduit of course, to make sure there was no voltage drop. Same on the trailer but just some 8mm to join it for half a metre round the trailer likage.
FollowupID: 355555

Follow Up By: drivesafe - Sunday, Feb 06, 2005 at 13:45

Sunday, Feb 06, 2005 at 13:45
JohnR, No matter how large the cable is, you will still have a voltage drop, it will just be less. The problem is not just how large the cable is, but also how LONG the run is between batteries.
While charging, check the rear battery voltage against the voltage at the front of the vehicle and if your rear battery is low, there will be at least a half volt drop or more depending on how low the rear battery is.
FollowupID: 355556

Follow Up By: Member - JohnR (Vic) - Sunday, Feb 06, 2005 at 14:10

Sunday, Feb 06, 2005 at 14:10
drivesafe, you are right to an extent that the alternator has to run long enough. We are talking cables as big as you little finger including insulation, or without the insulation for the cable I have if I want to use it. When you have voltage drops of several decimal points, you are talking none in the scheme of things. The supply cable in the LC we put in is begger than many jumper leads you can buy. You can look up the LCOOL chart if you really want. The drop is stuff all.

I have some 400 amp welder weight leads if I want to get serious. The main problem is the quality of clamps.
FollowupID: 355561

Follow Up By: Nick R - Sunday, Feb 06, 2005 at 20:18

Sunday, Feb 06, 2005 at 20:18
Just an addittion to JohnR's comments,
The cable was 25 sq mm which was second hand. We used to drag 240vac through it @ up to 130 amps no probs. 3 cores of the stuff ran our dairy for over 13 years
The lcool calculator says the drop is nine tenths of bugger all.
once it was in conduit twas fun getting it up the chassis rail!!!
with a slight change to the ends it should power a winch I expect

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FollowupID: 355594

Follow Up By: drivesafe - Sunday, Feb 06, 2005 at 21:10

Sunday, Feb 06, 2005 at 21:10
Hi JohnR and NickR, I am not saying you are incorrect to use the heavy cable but you will find that there are some differences between 240 AC operations and 12 Volt DC. With long cable runs at 240 volts AC you can loose 10 volts and have no noticeable difference in the operation of equipment. This is only a 2.4% drop.
Even with heavy cable, because of the distance, a 10 to 15% voltage drop is common place and as I posted earlier, wait till you have a low charged rear battery and once you start your vehicle, measure the voltage drop and you are in for a surprise, NO MATTER how thick your cable is.
My point was that ANY size cable can be used but yes your thicker cables is better but most people can get by with the cable size posted originally.
FollowupID: 355599

Follow Up By: Member - JohnR (Vic) - Sunday, Feb 06, 2005 at 22:46

Sunday, Feb 06, 2005 at 22:46
ds, I suggest you come and check the cable to prove it wrong mate.

25mm square cable is a long way better for the charging than 8mm which is the point I made earlier. I am aware of the difference between 240v and 12v or 13.8 at charging and once again the voltage drop is minimal in comparison to 8mm cable, even over 4 metres.

I have seen many times voltages of 100 metres for 240 volts with less than that because the drop has been calculated for the current draw. Bigger cable you may understand

That said we still see people use 6mm and it will still slow down the charging over a distance longer and it takes longer because the voltage drop is greater as you acknowledge - actually you don't acknowledge.

Most people I know can understand the analogy of trying to force 1000 litres of water through a half inch pipe versus a 2 inch pipe. It will take a hell of a lot of pressure/energy or time to get it through the half inch pipe in comparison to the 2 inch. ds 12 volts is low pressure electricity.

Too small a cable will reduce the capibility of charging or over a distance allow heat to build up and burn the insulation and possibility the vehicle if the draw is too high. If you chose to use a small cable from the front of a vehicle to the trailer you will find the battery doesn't charge even if you drive the daylight hours, running the fridge as well, because of the voltage drop. That is the reason why some may think they need to have a different battery and can't get it charged
FollowupID: 355621

Reply By: drivesafe - Sunday, Feb 06, 2005 at 13:14

Sunday, Feb 06, 2005 at 13:14
Hi Paul, I would personally use a deep cycle in the camper because it can be left for longer periods between charges.

The cable you suggested is fine as long as you take two things into account.

One, you can use any size cable to charge the rear battery but make sure you protect the cable from shorts and overloads, EG. put circuit breakers at both ends and use a circuit breaker with a rating no greater than the current rating of the cable you are using.

Two The lager the cable the quicker the rear battery will charge. If you had to, you could use speaker wire to charge the battery but it would probably take days not hours to put a decent charge back in the battery.

Next, your alternator will easily charge up all three batteries but this will depend on how fast you are going, IE. how fast the alternator is turning.

Your cranking battery will probably pull 20 to 25 amps for about 30 seconds and then drop off over the next 10 minuets to a basic charge current of no more than about 4 amps.

The amount of charge that the other batteries pull depends greatly on how low they are when you start to recharge them but the absolute maximum current draw for each battery after the first minute or so, is again about 20 to 25 amps for a short time and that will taper off as they charge.

As for how much you can get into them, you may or may not reach 100% but you will get to 95 to 98% depending on how long you drive for.
AnswerID: 96937

Follow Up By: David Au - Monday, Feb 07, 2005 at 09:08

Monday, Feb 07, 2005 at 09:08
Drivesafe> what a load of absolute bull manure "Next, your alternator will easily charge up all three batteries but this will depend on how fast you are going, IE. how fast the alternator is turning. "

Drivesafe you know little about nothing and even less about anything to do with batteries or twelve volt systems. Drivesafe toddle off back to nanny gregor for a nappy change.
FollowupID: 355652

Reply By: Member - muzzgit - Monday, Feb 07, 2005 at 02:19

Monday, Feb 07, 2005 at 02:19
Use the heavy cable, and connect POS and NEG direct from camper to second battery in car with circuit breakers, don't try to earth from chassis. Make sure you insulate it properly, someone here mentioned pvc piping, perfect !! Convoluted tubing is good too. Use a 50 amp anderson plug at the rear of the car, and swap batteries between car and camper if you want faster charging.

Isolator switches in the patrol MUST be spike protected, Redarc is a good one !

If you think you won't be driving enough to keep power for everything, I would recommend a generator for longer trips. Anything over 3 days without much driving and I'm stuffed without my gennie. The deep cycle in my patrol will happily run the waeco and a SMALL fluro with only a little 4WDriving each day on long weekends and such, but that's about it.

I'm surprised others on here havn't tried to talk you into solar panels 'n stuff, but not everyone's got the mulah for that, am I right amigo !
AnswerID: 97033

Reply By: Paul - Monday, Feb 07, 2005 at 08:39

Monday, Feb 07, 2005 at 08:39

Thanks for the input, so in short I'm thinking Deep cycle in the Camper, 2nd Starter in the car, rewire with thicker cable and away I go.

Yes already thought about solar panels but they are outside my budget.



AnswerID: 97044

Follow Up By: David Au - Monday, Feb 07, 2005 at 13:36

Monday, Feb 07, 2005 at 13:36
Paul while solar panels at this point in time may be outside your budget, have you thought of using a small solar panel to maintain your battery in proper condition and fully charged state when not in use. A 12w solar panel and SHS6 Morningstar solar controller can be had for $230.00. This cost should be recouped in the life of the first battery. For an extra $30.00 you could get the larger regulator SHS10 and add a 110w panel ($715.00) when funds are available.
FollowupID: 355713

Follow Up By: drivesafe - Monday, Feb 07, 2005 at 13:45

Monday, Feb 07, 2005 at 13:45
Hi Paul, don’t forget to put circuit breakers at both ends of the cable near the battery terminals, no matter what size cable you use. If you have an accident or jack knife and pinch the cable, you are going to have a massive amount of current shorting.
FollowupID: 355716

Follow Up By: David Au - Monday, Feb 07, 2005 at 15:00

Monday, Feb 07, 2005 at 15:00
Drivesafe more bad advice. Drivesafe how about you toddle off and find some proper education in this low voltage automotive field. Virtually every post you give incorrect, wrong, misleading or ill informed technical information.
Drivesafe nanny gregor at overlander babies is calling you
FollowupID: 355724

Reply By: MrBitchi - Monday, Feb 07, 2005 at 14:05

Monday, Feb 07, 2005 at 14:05
If you have an isolator fitted (Redarc or similar) the cranking battery will charge first, before the isolator connects the auxillary batteries. Once the cranking battery is charged then its just a matter of how long you run the car as to how much charge you put back in the auxillaries. Maybe you wont get a 100% charge in a deep cycle but if you're going to run it down regularly then a deep cycle will survive a lot better than a cranking battery. That's why they call them 'deep cycle' :--))

You'll find lots of people on this site endlessly arguing about .1V here or .2V there, 90% charge v 95% charge and getting all hot under the collar about it.
AFAIC as long as the fridge runs she's OK. Fridge stops, time to go for a drive. Redarc means cranking battery never gets affected by fridge.

Quote:-Only reason I hesitant about Deep cycle is you never get them back to 100% charge when out the middle of nowhere as the require 15-16Volts to charge up to 100% /Quote
Duh?? first time i've ever heard that one......

Cheers, John.
AnswerID: 97096

Reply By: Member - Hugh (WA) - Monday, Feb 07, 2005 at 15:44

Monday, Feb 07, 2005 at 15:44
Hi Paul,

I have a GU Patrol and camper trailer.

I have twin battery set-up (bothing cranking batteries) in the GU via a Redarc solenoid. For the camper I fitted a hybrid (marine) battery which is cranking but can handle being drained on regular basis. I get all my batteries from Challenge Batteries here in Perth (I think they brand them as PowerBreed). I have used 6B&S cable (25mm2) via a 50A anderson plug to charge the camper trailer battery. I put a 50A circuit breaker ~ 5cm after the Redarc solenoid on this circuit.

I charge both auxilary batteries in parallel from the Redarc solenoid i.e. have cables going to each battery. I figured for most of the time it only charges the second battery, and for those occasions when the trailer is in tow any voltage diff between the auxilary batteries will even out when connected and charge as one.

This has worked out OK for me for past 12 months or so.

Good luck with your set-up.

AnswerID: 97106

Reply By: drivesafe - Monday, Feb 07, 2005 at 15:48

Monday, Feb 07, 2005 at 15:48
dave, before you make comments about how much someone else knows or doesn't know, I think you had better go and have a read of Standards Australian.

Paul asked a question relating to automotive voltages while you rant on about low voltage.
Low voltage relates to AC voltages between 100 volts and 1,000 volts or DC between 120 volts and 1,500 volts
Automotive voltages fall into the category of Extra Low Voltage.

Paul, one more thing, if you are going to be buying cable, make sure it is Automotive cable. It was mentioned earlier in this posting that someone was using AC cable. Thats OK for them but Domestic AC Mains cable has a lower flash point ( can ignite at a lower temperature ) that automotive cable plus AC mains cable is usually made from thicker, but less copper strands, while Automotive cable is made up using more but thinner strand. The reason for the thinner strands is to make the automotive cable more flexible so that it won’t go brittle and break caused fatigue.

AnswerID: 97107

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