Battery Charging

Submitted: Monday, Jan 20, 2003 at 12:32
ThreadID: 3029 Views:1474 Replies:5 FollowUps:6
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I have searched the archives and found a lot of stuff about fridges, batteries, generators, solar panels but all I'm looking for is a simple answer.

I have a couple of fridges. One Liemack one engel.
I have a dual battery system on the car and an extra one on the camper.
I don't have the money to buy solar panels or an EUgenerator or eqivalent or expensive deep cycle batteries. They are all N70 normal start batteries.
I am not an auto electrician but would like some advice in layman's terms.
I do not want a long list of "should have's" or other recommendations/options unless they are really cheap.

Question is :- Whats wrong with just charging the camper battery off the vehicle battery using jumper leads ? Obviously you would need to have your car started & running for a while ! Secondly if this is possible how long would it take to charge back up say from 11.5volts
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Reply By: OziExplorer - Monday, Jan 20, 2003 at 13:31

Monday, Jan 20, 2003 at 13:31
David the problem with hooking your second battery up in the method you describe, is you are not getting the full charge into the battery from the alternator. You are only getting the potential difference between the two battery voltages. The alternator only senses the battery that is most fully charged. This could result in requiring quite a time to fully charge.

The cheapest and best solution for your case is to get a dual battery switch preferably with a field isolation switch built in.
Supercheap carry these switches and they are not that expensive. I don't know if the one they carry has the field isolator switch.
These switches are designed to be hooked up with battery cable.

The switch can have these possitions.
Battery One
Battery Two
or just the first three.

What you would do is start on your main battery, and then switch over to your second battery.
Now, you would have to check with an auto electrician if the alternator you have is safely switched at idle without a field switch. Most alternators at idle are ok, but don't take this for granted as some Hitachi models are not and will require a field switch before change over.

Just thinking about this, a battery switch with BOTH on would be better if you discharge the second battery to much. Some alternators require sufficient voltage to sense to start charging. If you flattened the battery to much then the alternator would not sense and charge the battery. If you had BOTH on the switch, the fully charged battery would then start supplying some charge to the second battery, and once it had come up somewhat, you could go back to idle and change the switch over to that battery on its own to get full charge. This system would need to be totally independent of your present dual battery system, or would need to be incorporated into your dual battery system to override it and work as described so you got full charge into the battery from your camper.

As to how long, well it depends on the battery size and the size of your alternator and the state of charge. An amp meter would be a useful device in the circuit so you know what is happening in that second battery. I think at the Supercheap etc. they can be had for around $15.00

I am not exactly rapped in using jumper cable leads. These do damage the terminals to ensure a proper connection, can come off or not make a good connection which could fry your alternator. A good eye terminal would be better solution with a wing nut terminal.

AnswerID: 11574

Reply By: bruce.h - Monday, Jan 20, 2003 at 15:18

Monday, Jan 20, 2003 at 15:18
david if money is an isue you can alway swap the batteries over placing the 1 from the camper in the vehicle to charge it & placing the carged one in the camper, bit time consuming but might be a tempery fix till you can aford abetter solution
Regards Bruce
AnswerID: 11578

Follow Up By: David - Monday, Jan 20, 2003 at 15:38

Monday, Jan 20, 2003 at 15:38
Thanks Bruce. That is what I have been doing up til now. But it is a bit tedious after a while and when I am on holidays I either want to rest or be out there exploring.
Money is always an issue as there are eight of us in the family. Me the wife plus 3+3 kids. We can't afford to hop on a plane for holidays therefore use the camper trailer for our family holidays.
When you ad up the cost of the 4wd, the camper, 2 fridges options on both vehicle and camper, camping equip etc it all adds up to a big investement that for most of the year to just sit in the shed. I have to draw the line somewhere and I think I have reached the point where I gotta stop buying things or else I will need a backup vehicle to carry all the stuff!
FollowupID: 6515

Follow Up By: Bruce.H - Monday, Jan 20, 2003 at 17:18

Monday, Jan 20, 2003 at 17:18
god i know that feeling
FollowupID: 6520

Follow Up By: Oziexplorer - Monday, Jan 20, 2003 at 17:55

Monday, Jan 20, 2003 at 17:55
I think we all know that feeling.

David with your Liemack drawing over double of all other brands of fridges, have you considered selling both your fridges and buying one of the larger Evakools or Waecos. This would dramatically reduce your battery consumption.

With the two fridges if they are in reasonable condition, you probably can sell both and get a new EvaKool or Waeco for the same price without any cash outlay and substantially reduced power consumption. e-mail them for their new brochure.

David if you are handy you could find a Victa lawn mower motor and rig it up to a generator or alternator to charge your batteries. Depends if you have enough space to carry something like that. There are often some real gems at the local tip shop in the way of Victa mowers. I will forwarn you, the shaft on the Victa is not standard and you will need to get somebody to machine a pulley to fit on the motor. Cost should be no more than $25.00 as it is not a major job.
FollowupID: 6523

Follow Up By: Bruce.H - Monday, Jan 20, 2003 at 20:16

Monday, Jan 20, 2003 at 20:16
Gday david
ozi got me thinking once saw on a squaters shack a car alternator set up with fan blades to to run it thus chargeing the battery not quite sure how it worked but if you rig it the wind of driving along would drive the alterantor charging as you went along no need to swap batteries it might sound abit flaky but hay it worked on a stationary shack so who Knows
Regards Bruce
FollowupID: 6526

Follow Up By: David - Tuesday, Jan 21, 2003 at 10:49

Tuesday, Jan 21, 2003 at 10:49
Following on from Ozi reply re selling the fridges. This is not an option as the small engel is the only fridge that fits behind the Prado seats when we are all in (8 of us) and is used for keeping things cold when we do our day trips. When travelling or at camp the Liemack stays with the camper.
Yes the Liemack does draw a bit of power on startup but over a period of time ie 24 hrs has averaged between 1.8 amp/hrs to just under 3 depending on temperatue settings on fridge and ambient. The problems I original had with the fridge were from 1. wiring (bad earth) and 2. The brand new 70amphour battery was only delivering 40amps.
FollowupID: 6557

Reply By: Eric - Monday, Jan 20, 2003 at 23:22

Monday, Jan 20, 2003 at 23:22
The rate that a battery charges is determined by the voltage aplied to it and its state of charge at the time. The alternator does not sense the charge of a battery but puts out a constant voltage. your alternator is capable of charging all 3 of your batteries without any problems if you voltage regulator in your alternator is adjusted corectly it will charge any batteries connected to it at a maximum of 8 amps per battery. The way the wiring in the vehicle is arranged limits the charge by using the resistance of the wire from the alternator to the battery, So if you want to charge the second and third batteries you must run a new wire from the large terminal on alternator to the other batteries via a switch or a relay operated by the ignition cct. Make sure that the wires are run in a way that the insulation wont rub through and start a fire, if you can find a piece of old garden hose to run the wires through this will be as good as conduit. The time the batteries take to charge is calculated by the capacity divided by 8 so you n70 will take 9 hours from dead flat. dont let anybody tell that you can charge a battery faster than 8 amps without damaging it it is simply not true. Eric.
AnswerID: 11611

Follow Up By: Phil - Tuesday, Jan 21, 2003 at 11:56

Tuesday, Jan 21, 2003 at 11:56
At last, someone who knows what they are talking about!
The output voltage of the alternator is essentially constant, although there is usually a temperature compensation built in to account for the different voltages required when battery temp changes. A crude approximation since regulator temp and battery temp may be quite different, especially if one is in a different compartment. The fact that the alternator is rated, say, 70amp does not mean that it will charge at that rate, only that if you have a huge number of accesories running it can supply all those extra amps and still keep the voltage correct to charge the battery. A battery will only accept a relatively low charge current unless the voltage is much higher than the regulated voltage in a vehicle. Phil.
FollowupID: 6560

Reply By: Member - Steven - Tuesday, Jan 21, 2003 at 17:35

Tuesday, Jan 21, 2003 at 17:35
hello david
1 a suggestion as your 2 sub batteries pack up you change them to deep cycle i know about extra cost but it is well worth it.
2 i wired my own second battery myself (deep cycle now but originally just a normal battery) it comes from main batteryto second battery via a full time or constant heavy duty solenoid which i can control with a switch under the dash .it is wired with battery cable and from it i run my van on 12 v0lts plus 1 fridge in back of car uhf radiohf radio when fittedand touch wood its 18 months old and still performing (century battery $175 but worth every penny) i believe that as long as you run 6mm+ cable to your plug you could put a switch under the dash to swap from charging second car battery to charging van battery with out to many problems and a lot of expense (this is assuming that you can do the work yourself and save the dollars it is not hard work you just need the know how cheers steve
AnswerID: 11636

Reply By: Ozy traveling Aussie - Tuesday, Jan 21, 2003 at 18:14

Tuesday, Jan 21, 2003 at 18:14
As you have stated your Liemack fridge is NOT power hungry at only 1.8 amp/hrs, I have a 50ltr Liemack fridge/freezer running @1 and -14 degree's with the same low power requirements as you have posted.

I fully aggree with Eric and Phil, however the leads must be capable of delivering without a power drop. "Ozzie's" idea of the 3 way switch to charge the camper trailer battery and/or the second car battery would be of great benifit to you, however with a Manual switch you have to Remember to turn it on as required....
AnswerID: 11638

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