Battery charging options in camper using computer power supply

[josh9465]

I like the idea of the Redarc BMS1215 battery management but they cost $1K+

im after something that does all. i cant seem to find anything else that does the same as the Redarc and is cheaper.

what i was thinking of is to get a DC to DC battery charger (Ctek D250S) and using a computer power supply so when im connected to 240V the charger will use 12v from the computer power supply.

when im on the road, the 12V from my start battery will also be hooked up to the DC to DC battery charger. (id use a relay of course to trigger 12v from battery when ignition on) and avoiding using mega thick cables and an anderson plug to camper battery.

if i wanted to use solar id get a solar regulator which is cheap and hook it up to DC to DC charger aswell.

so all up i reckon it will be cheaper.

what i need to know :

1, is the computer power supply able to power up a DC to DC charger safely.

2, if running 12v to DC to DC charger will it able to top up the battery whilst a fridge is running at the same time. (3/way fridge at 120W)
using online calculators 120W at 13.8V = about 9amps.

to me it looks possible.

[anthonygubbin]

Originally Posted by josh9465

I like the idea of the Redarc BMS1215 battery management but they cost $1K+

im after something that does all. i cant seem to find anything else that does the same as the Redarc and is cheaper.

what i was thinking of is to get a DC to DC battery charger (Ctek D250S) and using a computer power supply so when im connected to 240V the charger will use 12v from the computer power supply.

when im on the road, the 12V from my start battery will also be hooked up to the DC to DC battery charger. (id use a relay of course to trigger 12v from battery when ignition on) and avoiding using mega thick cables and an anderson plug to camper battery.

if i wanted to use solar id get a solar regulator which is cheap and hook it up to DC to DC charger aswell.

so all up i reckon it will be cheaper.

what i need to know :

1, is the computer power supply able to power up a DC to DC charger safely.

2, if running 12v to DC to DC charger will it able to top up the battery whilst a fridge is running at the same time. (3/way fridge at 120W)
using online calculators 120W at 13.8V = about 9amps.

to me it looks possible.

I was talking to an auto electrician re the benefits of a DC-DC charger and to be honest they are not worth it. I spent hours and hours for two weeks trying to work it all out, came up with waste of money. The main benefit is to fix the problem of voltage drop. On a camper trailer you will have virtually none if you use 8BS. I have a caravan which no doubt is longer than your camper and I have virtually no voltage drop and the distance is over 8m. Your alternator will put out 13.8v and there will be enough amps to charge your batteries. Having said that if you deep discharge them say below 11.8. The you should be looking to give them a full deep charge overnight using a 240v charger that way you will not shorten the life of the battery too much.

But don't take my word for it, I encourage you to talk to an auto electrican mate because I am sure they will say the same as my local one did.
Do some googling on the caravan sites as well because people have done the DC - DC thing and really it has not been worth it. Better off spending a few hundred and getting a decent solar set up 120w or a little more should keep it reasonably charged. Also buy a decent multimeter and keep and eye on the voltage of your aux if it hits 12v run the car for 10 mins and put some charge back in. If your fridge is drawing 9 amps I would only use it on 12v while you are driving as 9 amps will be like 4-4.5hrs on a 75ah battery before it needs a full deep charge. Unless of course you have a few batteries or a big mutha, or you have Ultima's in there.

Regards A

[kj69]

http://www.ausjeepoffroad.com/forum/...71#post1247871

[josh9465]

i think this is the answer to my question:

Hi Steve, that’s the irony, to get these DC to DC step ups to work at their best potential, you still need to have decent size cable, but you don’t have to run as thick a cable size as you would to allow an alternator to charge a battery at an efficient current rate and voltage level.

These devices will work from a lower voltage source but it’s at a need to have a greater current supply and the two become dependent on each other.

If you don’t run thick enough cable for these devices, you need a higher current supply so you cause a bigger voltage drop and you very quickly get to a point where the current draw is so great that the voltage drop caused will drop the voltage below the minimum operating voltage level of the device.

So your running thin cable in the first place, you may still need to run thicker cable before you can get the DC to DC working at full power.

Add to this the fact that if after fitting cable suitable to allow one of these step ups to work to it’s full potential, you then find you are still short of power, and you need to add another battery, you are now left with three choices.

1.) Leave your set up as is but plan on doing a hell of a lot more driving time to get your batteries charged.

2.) Rip it all out and fit decent size cable and let your alternator do what it’s been doing for decades before these wonder devises came along.

These device can charge a battery quicker than an alternator but it is in limited number situations and in the vast majority of cases, even with new alternators running at lower voltages, an alternator can still out do these wonder devices.

3.) Or you can spend the BIG bucks and get a Sterling, and you still need to run thicker cable!

[Wilf]

We have a D250S dual setup in our camper charging a 120amp/h battery and it is the ducks guts. Also have a solar panel on top so the battery is always getting topped up, best $300 ever spent.

[josh9465]

Originally Posted by Wilf

We have a D250S dual setup in our camper charging a 120amp/h battery and it is the ducks guts. Also have a solar panel on top so the battery is always getting topped up, best $300 ever spent.

how thick is your wiring from the car to your camper D250S

[rjl3175]

Josh that avatar is just disgusting.
This may or may not be useful to you guys but I have a charger left over from my R/C days. It charges from 12 and 240 volts, it will charge from 1-14 ni-cad or nimh cells Li-Ion or Li-Po 1-8 cells and lead acid from 1-6 cells.
Now I use this charger for all my charging needs, I have it between the fridge battery and the lighter socket in the back of the Wrangler and set it to 5 amps so it wont melt the wiring, hopefully.
These chargers are pretty smart and will even tell you if there is a problem like reverse polarity without taking out a fuse.
They can be had for about $200 from good hobby shops and the one I have has been going for about 6 years now and saved me heaps in battery cost.