24v to 12v converters...How big should I go?

[ScubaCat]

Looking to get one to add in to run 12V electronics. How many amps should I realistically look at drawing and still have headroom so as to not to run it at its top rating?

Is 40 enough for a good stereo, scanner, gps, radar, tablet 12v interior lighting etc etc.?

 

[74M35A2]

Radar? Those are typically kW (thousands of watts). Do you mean radar detector? Yes, 40a would be enough unless the stereo is running an external amplifier.

 

[TCD]

Things I would consider...

Howdy,

A few things you might want to consider when buying a simple step down converter are:

1 - The device should implement PWM technology
(https://en.wikipedia.org/wiki/Pulse-width_modulation)

2 - No load current draw: You don't want the converter to draw power if your are not using it. Otherwise you could literally kill your batteries while the truck is parked even is there was no 12 volt load on the system!

3 - Multiple electrical protections: The device needs to be capable of detecting and protecting itself and connected devices from at least: short circuits, over-load, high and low voltage fluctuations.

4 - 13.8 volt output: If you are going to charge 12 volt batteries or devices you will need an actual output of closer to 13.8 volts! Low voltage would also reduce the power of two-way radios and could reduce the functionality of other devices.

5 - Duty Cycle: For our use the device needs to be rated at the lower voltage as a "continuous service" and this will require a design that addresses cooling. A large unit may use built in fan(s) and require mounting in a well ventilated area.

6 - Be aware that "surge" or "start" voltage/amp ratings are usually for a time period of a few seconds at MAX! Always look at the "Duty cycle" rating (amps and time)!

7 - Fans are noisy, where are you going to mount the device?

8 - In our case the device should also be designed for rugged use.

I am building a camper in the bed of my 923A2 and I would rather have two smaller units (one in the cab and one in the camper) than one large unit with all of my eggs in one basket. Personally I am staying below 60% of the rated "Duty Cycle Load" for my units (if I have 30 amps of load worst case then I will use a 50 amp duty cycle rated device).

ALWAYS install a fuse or circuit breaker between your power source and the device!

As in most cases with electrical equipment you get what you pay for...

YMMV...

Happy Tails,
tom n tyler!

 

[ScubaCat]

This is what I was considering... Suggestions? Is there a better one I should consider? One with more headroom? If anyone here is selling them, they can speak up and I'll consider supporting them if the unit is appropriate...

http://www.ebay.com/itm/201534425593

 

[Recovry4x4]

The seller of that unit is actually a Steel Soldiers vendor. Suprman is his screen name.

 

[Artisan]

Why not just grab 12V only off the batteries?

 

[quickfarms]

Why not just grab 12V only off the batteries?

Ok if you just want to charge a cell phone but bad for a large power drain because it can lead to over or under charged batteries

 

[pmramsey]

Military PulseTech. They connect directly to the 24-volt system and you get eight more 24-volt circuits and four 12-volt circuits. None of your concerns or those mentioned here become an issue. Each circuit is fused in the distribution box and each is selectable as required using wedge type fuses up to 100 amps each. you can find them for $19 to $29 on the popular auction houses. These things are heavy duty and bullet proof. There is no reason to go or do anything else.

 

[603hellmutt]

I've seen those mentioned before, looks effective I've heard good things

 

[Artisan]

But 5 tons all have a small wire that goes direct to the
heater blower fan in 12V yes? Also my M916 uses
basically 24V for the starter and trailer lights for
the most part, the rest is all 12V

 

[74M35A2]

But 5 tons all have a small wire that goes direct to theheater blower fan in 12V yes? Also my M916 usesbasically 24V for the starter and trailer lights forthe most part, the rest is all 12V

Correct and yes. I do it this way also. The battery imbalance thing is a never-ending controversy. A lot speak of it, but there is yet to be any proven cases of it, at least here anyway. If the said converter limits spikes, it would be useful to power the ABS module with it so it does not go out to lunch on every improper shut down. I did this again just last night by reaching over and pushing down the switch I thought was the engine stop (without looking), and it was instead the battery switch. There goes the gauge needle off the chart again. I hate this stupid design.

 

[74M35A2]

Military PulseTech. They connect directly to the 24-volt system and you get eight more 24-volt circuits and four 12-volt circuits. None of your concerns or those mentioned here become an issue. Each circuit is fused in the distribution box and each is selectable as required using wedge type fuses up to 100 amps each. you can find them for $19 to $29 on the popular auction houses. These things are heavy duty and bullet proof. There is no reason to go or do anything else.

This is interesting and I found them, including their website, but it doesn't really say anything about the internals. For example, no current capability for the 12V or 24V outputs (does it use a DC-DC converter to get the 12v and is the 24v just straight through or also through a filter/regulator/converter), and also it does not say anywhere that it can/will act as a surge suppressor? Any additional info? I'll ask the directly via their website also. Thanks.

 

[74M35A2]

This doesn't look like anything more than a fuse block? I'm assuming it connects to both batteries, and simply uses one for the 12v supply. So, no different than tapping one battery. Please correct me if I'm wrong here.

 

[Jbulach]

I think you are correct, just going off memory, I think those Pulsetech junction boxes where to be installed with a battery equalizer (a lot more $) like the Surepower 100 amp, and a solargizer.
Think I remember seeing the whole "kit" for around $500???


M925A2 with dump hoist

 

[ScubaCat]

So, would it be more commended then to just run an additional 12v alternator to a lone 12v battery and be done?

 

[Jbulach]

So, would it be more commended then to just run an additional 12v alternator to a lone 12v battery and be done?

For big loads possibly.
I was looking at separating two of my four batteries and running them parallel to run my 12v winch in my bed.
I was thinking I might be able to use a 100a equalizer to keep the 12v side charged, but I'm not sure if it would handle the surge from a big electric winch. I was hoping the two batteries would provide enough of a buffer? Also, I assume I would have to run a disconnect switch, thinking the equalizer would drain the batteries while sitting


M925A2 with dump hoist

 

[VPed]

Correct and yes. I do it this way also. The battery imbalance thing is a never-ending controversy. A lot speak of it, but there is yet to be any proven cases of it, at least here anyway. If the said converter limits spikes, it would be useful to power the ABS module with it so it does not go out to lunch on every improper shut down. I did this again just last night by reaching over and pushing down the switch I thought was the engine stop (without looking), and it was instead the battery switch. There goes the gauge needle off the chart again. I hate this stupid design.

I have seen threads discuss the problem on here. From basic electricity training - current in a simple circuit will be the same everywhere in that circuit. If you have batteries in series (does not matter how many) the current will be the same to or from the batteries. The 12 volt tap between the two batteries being discussed here is adding a load (and eliminating the "simple circuit" description. The alternator is designed to charge the sum of both batteries' voltage to the regulator setpoint (the regulator has no way to sense what the voltage is between the batteries). This will result in the lower battery always being undercharged and the upper battery always being overcharged while charging from the alternator. Both of these conditions leads to premature battery expiration. The level of under/overcharge is directly related to the current being pulled off the 12 volt tap. A cellphone charging will take quite a while befog the imbalance is detectable. Larger loads will show problems more quickly.

To solve this:
A converter pulls equal energy from both batteries and converts to desired level.
An equalizer senses voltage of each battery individually and charges accordingly.
Periodically swapping the positions of the batteries reverses their respective previous under/over charge condition.
Periodically charging both batteries with a 12 volt charger will attempt to restore to designed charge level.
Periodically replacing the batteries with new. (the Govt. approach when you see center taps on active duty vehicles. (do not use the low blower speed setting on your heater.)

 

[ScubaCat]

According to the linked item, it has very little draw. It also has a 24v input and a 12v output, so the batteries levels should be equal, you'really not hoozing to only one battery. It just a matter of putting in big heavy duty batteries to give the RESERVE and cranking amps needed.

Pulsetech has a distribution box that has 24v in with separated, wired outputs for both 12v and 24v that I think would accomplish the same thing....