12v-12v chargers

[404pug Avid PP Poster! Find all posts View Profile Close 404pug]

I have an ABR battery box which has its own isolater built in and works fine with the 100AH sealed gel battery. However I am not entirely convinced that it charges fully over the course of a day's driving. It has the correct wiring size. Not usually a problem but on a 2-3 week trip it doesn't run the fridge as long without charging towards the end of the trip. I was wondering if a 12v.-12v charger would be better. What have people used? Have they worked? Are their any portable units around that can be easily moved from car to car? Costs? Neil

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

We need more info 404.

1. What are you plugging the battery into to charge it.
2. How far is it from the main battery?
3. What size cable is it all the way along to the main battery?
4. What vehicle type are you using?
5. Are you running a voltage booster?
6. What brand is your aux battery? (this is required to find out the charging profile of your particular battery)
7. How old is your battery?
8. How do you charge your battery when home and not in use and what charger do you use? and last at this stage,
9. What is the load in amps. You say a fridge (which is 3-5amps) is there anything else i.e. light etc.

Cheers

Winston...Good night.

[404pug Avid PP Poster! Find all posts View Profile Close 404pug]

1-connected to main battery via circuit breaker.- anderson plug into battery box
2 in the back of the 120 V6,via the appropriate heavy cable for both pos and neg.
5 don't need the voltage booster - the v6 puts out 14.2-14.3 v
6 not sure -100ah sealed gel deep cycle
7 3years
8charged from 240 v every 3 months via a multi stage charger
9 - just the fridge.
The question was a more general one about 12v-12v chargers and especially one which could be moved from car to car and not cost the silly prices being charged for some name brands. The system I have works, Winston . I was just wondering if there is something better and more efficient. Thanks, Neil

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

What do you call a silly price? CTek, Redarc and Anderson sell a DC DC charger, if not others, and all are similar in performance and price. I have a BCDC1225 Redarc mounted in the back with the AGM battery and it works extremely well, best charge i have had in a second battery, but I suspect it falls into the silly price range.

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

1-connected to main battery via circuit breaker.- anderson plug into battery box Nice
2 in the back of the 120 V6,via the appropriate heavy cable for both pos and neg. Is that 16mm2?
5 don't need the voltage booster - the v6 puts out 14.2-14.3 v What voltage are you getting when the vehicle is running (charging the aux battery) on the aux when the fridge is on it's coldest setting. i.e are you getting about 13.9 vdc at the aux battery?
6 not sure -100ah sealed gel deep cycle Need to make sure your gel battery is not getting too much voltage from the alternator
7 3years Might be starting to loose it's capacity
8charged from 240 v every 3 months via a multi stage charger Nice. may have to "recondition" the battery. Most multi stage chargers have this option. Just need to check if this is applicable with your brand of battery
9 - just the fridge. 2-5 amps would be fair to say?

If you can run the aux battery down to say 12.2-12.3dvc then without the fridge connected start vehicle increase rpm to around 1200-1500rpm and measure what amperage your aux battery is drawing. if it's more than 20amps then a DC-DC charger will not offer any benefit. If its less then that check the voltage as well. Might be as low as 13 or so volts. Note the voltage will will start off low and will increase as the battery charges. When you say heavy enough cable is it around 16mm2? You will also get voltage drop across the anderson plug plus and the isolator and connections. The isolator in the battery box, is that operated manually or electronic? The electronic ones like to be close to the main battery as possible depending on brand.

Winston.

[404pug Avid PP Poster! Find all posts View Profile Close 404pug]

ah ha . The set up is the battery box and cables -"Flyer" as supplied by ABR-Sidewinder and generally seems to work well. BUT.... it has an automatic isolator built in to the lid and this obviously at the end of about 3m of cable so it is possible that with the isolator so remote from the main battery that an issue arises there.nevertheless, a good system because 35 kg is not sitting in the front rhs cornerall of the time. it can be taken out of the car and only put in when needed. Neil. ps I had the auto sparky check it when some other work was being done and he said it all looked fine with negligible voltage drop from the main to auxillary battery.

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I just had a look at this website. I take it the battery box you are using is in this link http://www.sidewinder.com.au/page133.html ?

If you look at this link it shows the type of cable you are using to connect to your main battery http://www.sidewinder.com.au/page169.html

As you can see it's 10mm2 cable. Now refer to the following thread:

http://www.pradopoint.com/showthread...786#post423786 or

http://www.solarhome.ru/en/basics/ba...ing_cables.htm

If you want to supply 4 amps from your main battery to run your fridge using 10mm2 twin core cable you could do this over 17 meters.
Now you want to charge your aux battery also you would want around 20 amps, 16 amps to charge the battery and 4 amps to run the fridge but you can only do this over 3.5 meters. Using longer cable lengths and you start getting voltage drops. In turn your battery takes longer to charge. Your battery isolator might not work properly also. At 16mm2 twin cable you can do this over 5.5 meters.

With DC to DC chargers they require more current on the input (from main battery) i.e. 25 amps to supply up to 20 amps on the output (to the aux battery) so this would make the matter worse. You have no free lunch with these devices.
For example a 12vdc to 240vac 600 watt inverter will suck up to 50 amps from your battery (watts divided by volts = amps). You can only do this over 2.2 meters using 16mm2 twin core cable. You could in theory nearly double the length if you use the chassis or body of the vehicle as an earth but your connections have to be spot on and not degrade over time being exposed to the elements.

I hope this helps. Most common electrical issues are related to under size cables and or bad connections.

Winston.

[404pug Avid PP Poster! Find all posts View Profile Close 404pug]

Thanks, Winston - good, clear information. It explains why over 20 days on the CSR the second battery in the box you correctly identified did not seem to be as charged and the isolator did start to rattle or flutter.. I now have a bit of a work around which seems to be working: at the start of each day's driving I switch the fridge [ a 20 year old 40l Engel] over to the main battery which has had nothing running off it overnight and so charges quickly. This appears to allow the 2nd battery to get on with charging without having any thing drawing on it while it charges.
In more general terms then, if one was using a DC to DC charger to charge a battery in a caravan or trailer then much heavier cabling nees to be run through to it to make it work effectively? OR, in my case I could easily shorten the battery cables by over a metre and that would help?

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

pug do you know what size cable you have? The isolator is best located near the main battery but you can locate a DC DC charger at any distance as long as the cable is the right size for the current draw.

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

In more general terms then, if one was using a DC to DC charger to charge a battery in a caravan or trailer then much heavier cabling needs to be run through to it to make it work effectively?

Yes. I would still use 16mm2 as a minimum. The less voltage drop the quicker your batteries will charge. Need to measure voltage drop under load also. It's like testing your starter battery. You test the voltage whilst starting the vehicle.

OR, in my case I could easily shorten the battery cables by over a metre and that would help?

You need to measure your voltage drop to see if it's getting under 13.5-6v depending on your minimum charging requirements for your battery.
In my vehicle I have in the engine bay two 66AH Optima AGM D27F's batteries with charging requirements for an alternator of 13.65-15 volts. I use a Redarc electronic isolator, SBI12.

I also have a full river 120AH AGM battery in my camper trailer (came with it). My set-up has 16mm2 from the engine bay all the way through to the camper. Total length is about 11 meters. I went camping recently and was running led lights and a 60 Engel. Fridge running time was about 16hrs. When we left in the morning my scan gauge was showing 13volts (normally 13.8-14.1) and within 3hrs went back to 13.8v. I was running the air-con, had my lights on and a UHF. The reason the voltage was so low was as soon as you start the vehicle the isolator will turn on as it sees more than 13.2vdc from the main battery as the alternator will be putting out 13.8v or so. The isolator does not allow time for the main battery to charge before turning on.
So as a result the alternator is charging two batteries totalling 132AH. That's big. Now factor in that I also have a battery in my camper connected, total AH is now 252AH the alternator is charging. That is a big load hence why the big voltage drop. That's why I use AGM battery with a low internal resistance as they charge quicker. Normal batteries would take a lot longer to charge hence why people run in to trouble with their batteries running flat over time. One way around this is to use manual isolators between the main and AUX battery and between the AUX battery and the trailer / Caravan battery and select the main to charge first followed by the aux and so on.

DC - DC chargers will not help in 90% of cases and you would be better off having a 2000w generator (Honda's are very nice and worth the cost at the moment) buy a 25amp multi stage charger and you could charge up an AGM battery in a few hours. Normal batteries could take double the time. Or use solar panels on top of the caravan (as big as possible) and use a device that allows to to connect two input devices (in this case power from your solar and power from your alternator).

At the end of the day it is trial and error and what ever works with proper testing / application is all that matters. If you have a good set-up and have used it like you should i.e been camping for a week etc then share the knowledge. There are many ways of doing things. Two things you need to keep in mind is 1) Will it do the job that I require? and 2) Will I pay top dollar when there are cheaper more effective options out there?

I wish to do a video of my set-up running the batteries down and conducting tests on how long it takes to charge etc to give people a better idea of what is required. At this stage it won't be until Dec when I am on leave.

Winston.

[rob_macca67 Avid PP Poster! Find all posts View Profile Close rob_macca67]

Good Reading.....

A few years back I had a similar setup where I had 2 batteries under the bonnet and then a Battery in our Campertrailer. I had 35mm2 running between the 2 batteries under the bonnet with a Redarc 100A isolator between the 2 and then I had 16mm2 (might have been bigger as it was a few yrs ago) running down to a Anderson Plug for the C/T. After 3>4days of camping w/o starting the car, I noticed when it was time to come home the volts remained below what the normally are and I expected this.... After a few of these types of camping trips I started to notice that even though the Redarc Isolator indicated that it was closed, the Aux Battery Voltmeter told me something different. I sent it back to Redarc who informed me that the contacts were pitted & they replaced it for me....This whole scenario happened again and Redarc asked me how my system was wired and cable size. To cut a long story short.... the large cable I was using was allowing a high current flow to flow from the fully charged MAIN battery into the drained AUX & C/T batteries. They suggested to upgrade to the 200AMP unit which I did and I've never had any problems from that point onwards....

So, from that experience, I would suggest that any Isolator that people install should have at least the same "Current carrying Capacity" equal to the "Current Carrying Capacity" of the cables that are used to connect the MAIN & AUX batteries together..... This has just been my experience.... others may have a different opinion though