Thread: camper trailer questions...

In this case my charger would be my car alternator. So I'm really trying to confirm factually if it is possible to use the 12s socket to charge directly a 130ah AGM in a camper trailer.

Originally Posted by Ashes

In this case my charger would be my car alternator. So I'm really trying to confirm factually if it is possible to use the 12s socket to charge directly a 130ah AGM in a camper trailer.

It is possible of course Ashes but you need to learn what your current draw is likely to be before making the decision to go through the 12S socket. If more than 30A then no. If less then yes. Hopefully I helped answer your other q's

In addition. My belief (open to disagreement here) is that charging via an alternator is a fixed voltage charge. This means that the current is not limited or controlled by any devices and at say 13.8V or whatever the alternator gives the battery the current will depend upon the level of discharge. So heavily discharged batteries will take much more current than Lightly discharged batteries. Unfortunately I cant tell you how much but maybe others will help.

There is an issue with forcing batteries to take a charge as opposed to controlling with a battery charger. When the battery takes a large amount of current it gets hot. When a battery gets hot it is prone to damage or at the very least it's life is shortened but also, the heat increases the batteries own internal resistance. (That is resistance to current) so the current in the charging supply is reduced leaving your battery never to achieve a full charge. Multi- stage (smart) chargers (despite what others may say on here) charge in stages to keep your battery cooler during charging, therefore reducing the increase in Internal Resistance and will achieve a full charge. I am aware theat AGM batteries have a much lower internal resistance to normal wet types band this of course prevent them getting so hot during charging. Once fully charged they will switch into a float mode and can constantly feed the battery to keep it charged and in prime condition. There is a large advantage in charging batteries in a controlled way (unless you need them charged quick that is) but if like me you have your discharges calculated to only 50% charge and have sufficient means to achieve a charge back during daylight hours (Solar) then you are better off charging with a charger as opposed to an uncontrolled charging current from your alternator. Just think that you don't ever need to check battery charge levels before hooking up or in transit!

Yep agree. I use a multistage 240v 7A Ctek to charge the camper battery when mains is available. I'm now looking at options for recharging when off the grid for when I'm stationary and topping up the battery when touring.

For the record I'm dubious that the 12s socket and wiring has the capacity to sustain charging amps to a heavily discharged camper battery but it is there as an option and there seems to be little information available as to its real world capability on a D3/D4.
I can also understand how it is difficult to specify what can be done with it but surely some facts exist on volt/amp rating of the wiring to the socket.

Ashes

12V 30A Thats the rating. Unquestionable. The question is what will you pull through it?

That is definitely the key question. At the moment it would need to potentially handle charging needs of a flat 130ah AGM battery. In future that may well turn into 2 x 130ah batteries or more. These things tend to happen with upgrades and as needs change..

I don't know enough about the D3 electrics to know if the 12s circuitry will allow more than 30amps to be drawn through it. Obviously the fuse will do its job if you exceed 30amps. Does the electrics have some smarts in it to limit current draw on that circuit even if a camper battery is demanding more than 30amps of charge.

Given that pretty much every rear Anderson solution uses 6b&s connected to a main or aux battery in the car and a 50amp rear plug to hook to the camper battery this suggests to me that you would not normally exceed a 50amp draw for even a large battery bank in the camper and I sure there are guys out there running 200-300+ah battery systems. Is the max amps being supplied to the rear more governed by the capacity of the alternator regardless of the demands being placed on it by flat batteries? What would a standard D3 alternator be able to supply? I'm guessing in practical terms that it is less than 50amps or we would hear lots of stories about fuses or circuit breakers continually tripping when charging flat camper batteries.

I've just come off the phone with Redarc and the information I have is that my wiring must be able to sustain the max rated outout of my charger.
The charger will not exceed its rated output and so mine, even if connected to a flat 100A/hr battery, will run at a constant 25-26Amps and no more. I am therefore going to go with a 12S plug battery Positive (30A) as opposed to re re running cables and Anderson plugs/sockets.

I can't help you with your question though Ashes. If you are proposing to charge these batteries directly from your alternator I would imagine that the charging current might be much larger than the LR wiring is designed for and think that a larger cable would be required, possibly even larger than 50A.

It is your batteries which will demand the current from your alternator. As I mentioned before, the alternator uses a "fixed Voltage" charging method which essentially means the batteries take whatever current they need during the charge. You will need to be careful here as too much and they can lose longevity and the price for two new 130's isnt low. A charger will charge your batteries in a more controlled manner (boost when needed) and float them when charged, condition them, will achieve a 100 % charge as opposed to around 90% from your alternator and will prevent excessive current load on your on vehicle wiring and perhaps allow the use of the 12S socket with no mods.

Thanks for the info. Was hoping to avoid having an extra charger but there is some merit to installing something like a Ctek d250s. This hopefully would allow me to charge at up to 20amps from the 12s socket and also while camped could take a feed from solar panels in the future.