Hello I'm in the same
Hello I'm in the same situation, I just bought a BJ74 with the head unit wired through the battery with a load of other wires (guessing for amp and sub) in just a huge mess so decided to rip everything out and start over. Was thinking of buying an Aerpro 24v to 12v converter, but not sure where to connect to. My cigarette lighter and Clock are always on, is this normal or do I need to rewire that too? Any help is much appreciated, been wrapping my head around this for a while.
Hi
I would suggest to 1. bring the 24V setup back to close to factory standard and eliminates any 12V crappy installations.
Clock always on is normal, lighter probably too (depends on model).
Then 2. add a thoroughly designed separate 12V setup with a 24V to 12V converter.
To design this you should carefully think about where in the car you need what power for what type of appliances. Also consider whether there is a need for a dual battery setup. First you need to calculate the maximum power (Watt=Amps*Volts) your desired appliances would draw. This determines the size of DC-DC converter, main fuse rating and main wire gauge to use.
On general bases (and based on my own experience and mistakes):
- If a dual battery setup is considered (even only later): The dual battery will be 12V. Invest in a DC24-DC12 charger+converter right from the beginning. Otherwise you have to replace the converter by a charger later. (Which is rather not a cost- but a space- and wirering- issue).
- Place the main fuse next to the battery and connect directly to battery 24V terminal. Do not 'steal' from anywhere on the factory harness.
- The DC-DC converter puts a low but constant draw on the battery. Usually the rig can sit for more than a week with no issues, but on longer parking periods you may want to shut it all down. So put a main switch right after the main fuse. You could also place a relais controlled by ignition (see below), but most likely you want the 12V permanently on for camping, fridge and radio memory. I'd go for a manual switch.
- Run only one wire with 24V from the msin fuse & switch into the cab and place the DC-DC converters in the cab. Advantages: Your max load requires a less thick cable on 24V than it would on 12V, and there is little issue in crossing the firewall with one wire. Use an oversized cable, though, to limit voltage drop to the best possible extend.
- Put the DC-DC converter in the cab. Advantage: Lower ambient temperature is better for the device.
- As you draw from your starter battery, you need to monitor or (even better) protect your battery to maintain minimum capacity for a start. So put a voltage gauge and probably a battery protector in the main line. (Some DC-DC converters come with it).
- You will need a point for multiple fuses and distribution in the cab. So put a fuse box with required amount of slots in the cab, as close to the DC-DC output as possible.
- Run cables from that distributor fusebox to the consumers and connectors (radio, sockets, USB etc).
- If you want some 12V appliances to be switched by ignition key (e.g radio):
Place a decently sized 24V relais and wire it like this:
-- 12V from the fusebox to the relais' working circuit.
-- For the control (coil) circuit: 24V from ignition. The Toyota ignition usually has a position 0 (key just in & locked by this release knob), 1 (Certain consumers on, e.g. lighther), 2 (ignition on, run-position), 3 (starter).
Position 1 is what you want. Check which consumers turn on in this position. This may vary by model. In most rigs there is an ignition controlled connector on the harness already to fit a 24V radio. In my BJ73 the lighter is on this position, too. Steal 24V from such an appliances on it's connector, and feed into the relais control (coil). (This is the only occasion where to interfere with the factory harness connectors.)
-- If multiple appliances shall be switched by ignition, you may need a splitting connector or even a 2nd fuse box behind the relais.
- Make sure to apply proper electric Installation best practice ( crimped connectors, shrink tube, cable channel & fixation) and use properly calculated wire gauge, according to expected load.
On longer stretches, consider voltage drop and use oversized cables.
My 12V setup is designed for 240W total load (max load capability of the DC-DC converter). So my main fuse is 20A. My converter, 12V fusebox/distributer and battery protector (with build-in voltmeter) sit at the bottom of the center console. (Under this tray).
I have combos of 1 socket + 2xUSB 3.0 outlets in the trim panels on the front and on the back door, and I have a 2xUSB-inset in the 24V lighter. (Sockets are fused 10A, USB 5A, so that's 30A total -> my setup is not correctly calculated and undersized. I must not use all outlets in parallel at max load!).
There are nice USB outlets that feature a build-in switch and even a voltmeter.
I use USB appliances as far as possible as those draw minimum load, e.g. USB-based LED lights for camping, Bluetooth speaker. Only my fridge utilizes a socket.
Good Luck on your project.
Cheers Ralf
