On modern cars the alternator is entirely controlled by the engine computer. Voltage and current are both controlled based on temperature and the current needs of the vehicle.
What limits charging current?
- Thread starter Bailes1992
- Start date
Could you please share more info on this?
One of these...
T01 Car Diesel Heater, 12V LCD Automatic Control
Use of automatic control technology, the fuel, electricity, and temperature can be set arbitrarily, can cab heating of various 12V universal vehicles.
hcalory.com
I have a large void under by boot floor where one of these would fit nicely. There's a gasket on the bottom where you bolt it down to your floor (assuming it's flat) and the exhaust and air intake for the burner goes straight through the floor. If your boot floor is not flat then you can install a plate to mount it to but you'd need to seal the surface between the plate and the boot floor is air tight I guess.
I have enough room to feed the heater hoses either side of the wheel well, up the sides of the boot behind the carpets and install grilles on the shelves either side of the boot that the parcel shelf sits on. Essentially when the boot floor is back installed, other than the grilles on the trim on either side of the boot, you wouldn't know it was there.
You can either install an additional fuel tank, or what I'm planning to do is install a stand pipe in my fuel tank so it is supplied by the main tank. That will save having to fill multiple tanks and saves space.
I've spent a lot of time googling and looking at batteries. I have two reasonable options that I see.
The heater draws 15A to start, then 1-3A running. So a 30minute to 1 hour run on a morning would use 3-4Ah at most.
Option A - I like this battery...
It would fit nicely in the void under my boot floor. But it would need a DC to DC charger. A charger like the 9A version of one of these, which comes in around £60...
Orion-Tr DC-DC Converters Isolated - Victron Energy
Provide a stable DC output voltage using the, easy to install, Orion DC-DC Inverter from Victron Energy. Find a dealer near you.
Alternatively, I fit a 50Ah leisure battery like the type fitted to our caravan (but smaller). However, due to the height, the only place I could possible mount it is within the spare wheel itself (removing the spare wheel is not an option but luckily the spare wheel sits face down so there is a deep 'bowl' the battery could sit). I'd need to find a sensible and safe way to mount the battery to the spare wheel somehow, and in such a way that it's easy to whip out on the side of the road if/when I get flat.
The advantage here is being cable to fit a basic voltage sensitive relay and let the battery charge directly from the alternator. Having done some checks yesterday, the alternator seems to sit at 14.9v. However, I have a long journey tomorrow so will be able to monitor it better and see if things change on a long trip. That said, with the small amount I'm going to be draining the battery, I imagine it wouldn't take long to top back up. The only other negative is possibly having to fit a chunkier cable between the cars battery and this battery due to charging currents. I do have plenty of cable in the garage for that though. I guess I could empty the leisure battery completely, temporary hook it up to the car while running with a set of jump cables and measure the amount of current (worst case scenario) the battery accepts and design to that.
You won't need the "chunky cable." Current might be more at the get-go but a little voltage drop won't hurt your discharged battery. Then as the battery fills up the current will drop so the voltage drop will lessen, allowing the battery to completely charge.
That would depend entirely on the charging current rather than volt drop. I'm not remotely concerned with volt drop on a cable that would be 4m long. But I wouldn't want to fit an undersized cable as it would overheat and potentially be a fire risk.
That said, I did a 50mile/1 hour drive to work that allowed me to monitor the system voltage. Voltage peaked at 15.1v soon after starting and sat between 15.1v and 14.9v for 20miles before dropping down to 12.8v. Therefore a voltage sensitive relay isn't going to be appropriate. Therefore I'll be going down the smaller LiFePO4 battery route with the 30A 3 step charger.
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So I've bought a Victron Energy BAT212070084. It's an 8Ah 12v AGM battery. Cost £25 delivered.
I'm going to discharge it totally, connect it up to the car when the car is charging at ~15v and measure the current the battery takes. If it's excessive then I'll look for a charger. I'm hoping it will only be a few amps and I'll just fit an ignition switched relay.
I'm going to discharge it totally, connect it up to the car when the car is charging at ~15v and measure the current the battery takes. If it's excessive then I'll look for a charger. I'm hoping it will only be a few amps and I'll just fit an ignition switched relay.
Voltage drop will limit charging on that setup.That's what interests me. We have a caravan which has a 110Ah sealed lead acid battery in it. On the move it is charged by the car via a 20A feed which runs through a voltage sensitive relay and 2.5mm (approx 14AWG) cable direct to the caravan. So what limits the battery charging rate there? The relay is one of these...
RCT465
www.ringautomotive.com
These are about £10 vs £60 for a 9A 12v to 12v battery charger.
I have now decided on a LiFeP04 battery now which I've read won't be a good idea to charge via a smart alternator anyway. So I think these are out regardless.
I'm considering the Victron Orion 12/12v 9A battery charger now.
