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12v car power distribution

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Hon1nbo

Tue Jun 11 2013, 01:27PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

so I'm upgrading the power supply system in my car that runs my mobile transceivers (currently just an amateur tri-band mobile but adding an HF this week), as well as items such as an inverter and auxiliary sockets, and I am migrating all of the components to a new unit, an 80 Amp EZ-Gate from Hamsource, to maintain and distribute power from my auxiliary deep discharge battery.
Until recently I have been using a West Mountain Radio PwrGate, but it is only rated for 40 amps so I could not run my inverter and the like off of it, so those got a direct connection to the battery in the back seat.

The downside is that I realized the current selector on these units does not regulate the power supply draw as I was told. I currently run the battery charging off of a 12V socket from my vehicle, with charging current limited to 7 Amps. With the new equipment running off of the power gate, I need a way to prevent the unit from drawing more than 10-20 amps from the vehicle.
Problem is, these are simple OR-gate units using a couple of diodes for the power switching, they work by seeing whichever voltage is higher.

I thought about putting in an auto-resetting breaker, but that would not really solve the problem and be very inefficient (possibly tripping and resetting every time I key up the new transmitter at 100W).

The inverter is the main current draw, and would not be operational while the car is running usually, and if it is it would not draw as much power.

The most effective solution would be to run heavy gauge wire to my car battery through the firewall, but I am trying to maintain the original design that didn't really touch the car except to charge the battery.

Only other option I can think of is to make some kind of circuit that measures the current draw, and switches off the power supply from the vehicle using solid state means (to keep it reliable and handle switching repeatedly between transmitter key ups).

Thoughts?

-Jimmy

Shrad

Tue Jun 11 2013, 02:21PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

search for marine regulating charger

my father-in-law has a regulating charger which dispatches power from the battery OR low volt line OR wall via some switching regulators with battery charge management and all security cutoffs for less than $500 for a 40 amps unit

Hon1nbo

Wed Jun 12 2013, 08:25PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

Shrad wrote ...

search for marine regulating charger

my father-in-law has a regulating charger which dispatches power from the battery OR low volt line OR wall via some switching regulators with battery charge management and all security cutoffs for less than $500 for a 40 amps unit

These don't seem like they'd solve the problem in the end, just add more cost and in the end have a similar issue (drawing more from the power supply e.g. my car than it should). Also $500 for a 40A unit is way out of budget, I'm upgrading right now because my current 40A unit can't handle enough current between the battery and the inverter safely.
I'm thinking of just having a non-resetting breaker when I have more than 20A draw, which isn't that often. Biggest draw is the inverter, but I'm not usually using that at capacity while driving anyways. The socket from the car is rated for 10A, but the circuit it is on is rated for 20. I can just run some better wire if it even needs it. most of my time driving around I am receiving on my FTM-350, but not transmitting as much. Because of this the battery is usually pretty high in charge, so if the breaker trips I don't need to reset it until I get out of the car most likely.

-Jimmy

ConKbot of Doom

Thu Jun 13 2013, 12:51AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

If you dont want it drawing more then 10A, then dont use wire that can support more. A few volts of wire loss will limit current a good bit, and the wire wont get real hot if its not spooled up, or buried in insulation in a houses wall.

Figure out what sort of voltage differences youre seeing, you know your target current, use a wire AWG chart to figure out how many feet of wire in a certain gauge you need to get the right resistance.

suggest for 10A, anything over 20awg would be suitable, I'd personally keep it over 18 awg. (which looks like 10 feet would drop 0.6v each way with 10A passing though) Mind the ground size though, as I'm sure your antenna is 'grounded', so using the ground side to drop voltage may end up sending current over your coax, or other naughty stuff.

Just make sure to get higher temp wire then the plain PVC jacket stuff. The cross linked GXL automotive wire is nice stuff.

Ash Small

Thu Jun 13 2013, 09:59AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

May I suggest a different approach?.....insert a 1 Ohm resistor in series with the supply from the vehicle to the battery in the back. This will limit charging current to ~12A, but will allow you to draw more from the battery when required.

Changing the value of the resistor will regulate the charging current to whatever value you require, but will still allow the inverter to draw more current from the 'battery in the back' when required.

Total cost = one power resistor

EDIT: a ~100W (or two 50W in parallel) bulb would do the same job, and give a visual indication of charging rate, etc.

(this post has been revised as I got the figures wrong first time.)

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