My question is: What do I need in order to safely (and affordably) power my new battery?
The caravan currently has two charging paths, and I need to keep / upgrade both:
Via the 13 pin connector, directly connected to the 12v system in the caravan with no DC to DC converter. Guides online suggest that I need a DC to DC converter so I have no clue how this has been working.
Via a 240v shore power connector. The current battery has a built in charger, so it just plugs into a schuko plug connected to the campsite power connection and loads from there.
AC to DC
I need a charger that ideally will also plug into a schuko outlet and charge the battery while also powering the various little 12v loads in the caravan (fridge, lights, etc). I was looking at the Blue Smart 12v 15a Charger. Is this an appropriate product?
However, many campsites have varying amperage available at the pitch, ranging from 4a to 15a. Are any chargers able to adjust to the available amperage so that I don’t instantly flip a breaker when connecting to a lower amp circuit? Or do I need to use the lowest common charging amperage (so, get a 4a charger)? With a 300ah battery, I need to be able to use as much power as is available.
DC to DC My trailer has no converter, and it seems to work fine. What gives?
But assuming that I do need one: I took a look at some of the other threads on this forum, and it seems that people recommend the Orion Smart series. If I understand right, a 13 pin connector is rated for 20a max, but even the 18a Orion Smart could potentially overheat the trailer wiring after a long enough period of charging. Is the (rather expensive) Orion XS, limited to something like 15a, the only choice?
Or is there another product / solution I should check?
You are confusing input amps with output amps. Assuming you are in Europe with 230V ac, a 10A ac supply is 230 x 10 = 2300W. You will be charging your lithium battery at around 14V so with a 15A charger the power is 15 x 14 = 210W, allow for losses, say 240W. I would suggest a 30A charger minimum, that would charge your battery faster and still be less power than a 4A hook up can supply.
dc to dc charging.
As you had a small lead acid battery in your caravan this would have limited the current drawn along the charging cable so you did not need a dc to dc charger, although one would have helped offset voltage drop. A lithium battery needs a better regulated voltage, plus something to limit the current draw. An Orion DC to DC charger will be suitable. Many people add an extra positive and negative cable from the starter battery to the DC to DC charger in the caravan using something like an Anderson Plug.
If we are talking about the european 13pin trailer socket, then pin 10, unswiched battery positive, and pin 11, battery positive switched by ignition, should each have a 15A fuse. At least that was once standard.
Have you checked your cars fuses if it actually uses 20A for the trailer socket?
In the owners manual, it states that fuse F10 is “20 amps, ATO®, trailer charging cable”. That’s the most likely one I found that applies here. It’s a 2021 VW T-Cross, if you can verify my info.
What do you think would be appropriate to use as a DC to DC based on that, without retrofitting new cabling?
The previous one was a PowerXtreme X30 LiFePO4 though. Does that make a difference?
You are confusing input amps with output amps.
That is a huge point that I totally missed! Thanks for pointing that out. It makes the whole idea of the 300ah battery so much more reasonable if I could potentially charge it from dead in ~10 hours at a campsite. I’m looking at the IP22 30a 1C charger. Would you agree this is the appropriate (and affordable) solution here?
An Orion DC to DC charger will be suitable.
What specific one do you think would be appropriate to use as a DC to DC based on that, without retrofitting new cabling? As I mentioned, the 18a one seems to be close, but some people imply it would still be unsafe. I’m looking at the Orion XS, but it’s so expensive. I’ll do it if I have to, of course.
You had a small lithium which probably limited the current draw, you now planning a bottomless pit and this could draw more. It was not ideal to charge a lithium like that, it could easily get overcharged without a proper charger and you have been lucky it worked.
The 18A will draw 20A with similar input and output voltages, it will be above 20A if it is boosting voltage.
The only other suggestion is a DC to DC converter (not charger) which has a fixed output voltage which you would set to 13.5V for float. There is a 9A version, which is a bit low. You want something like a 15A version which does not exist.
A 9a charger would be fine for our use case, which is mainly to just keep the fridge running and keep the battery topped off between campsites. The 30a charger at the campsite is the biggest win here.
I noticed on one of the sites to buy the Orion 9a, it states explicitly that it should not be used to charge batteries. But you think that at 13.5v it should be ok?
If I use the 12v-9a charger, does this look right to you? It’s an isolated charger, so I wanted to verify that it’s okay to wire it together like this.
The model shown is an isolated one, so you can connect the trailer plug pin 13 directly to the orion input negative. Might make the wiring simpler, but either way works fine.
Since non-smart have no charge algorithms, i would set the output voltage only to float level, so about 13.5V. if the battery BMS has an allowed-to-charge contact, that could be used to turn the orion off trough its remote terminals
It will not charge when the output remains connected to the battery of the trailer/caravan, as it sees it like a short circuit, you must install a switch in the output.
My solution was to use a small timer relay, set at 5 seconds, which is connected to the +/- from the cable in the trailer.
The relay of the timer is normally open, when connecting the cable to the car, the relay stays open 5 seconds, then closes and the Orion starts charging.
But, you must also use a 0.375 ohm 50W resistor to limit the current to about 7-9A, mounted in the + line to the battery.
Otherwise when the trailer battery is really empty the Orion will burn up.
