Properly Wiring a Vehicle for 12V & 24V Devices Using 2 Batteries

[HyperSpeed]

I have some extra devices being hooked up on a typical 12V-wired vehicle. Because of the added load, the choice is to use 2 batteries, adding another. I would like the batts to be wired in parallel to supply the 12V devices. However, there are some devices I am running at higher currents which are 24V input capable.

Due to this, I would like to supply those devices with the 24V they can accept, to minimize power loss over the same wire size.

I know you can't series batteries on a common ground without a short occurring, of course. So how would the 24V circuit be setup so that the batteries still charge and no short occurs? I was thinking something like a high amp diode on the series wire, but I'm not sure that would prevent 1 battery from shorting. I'm also thinking the 24V devices would need complete isolation from grounding. I definitely reached the head scratching point, anyways.

If anyone may have a suggestion on a possible method for doing this right, that would be a big help. Thanks!

 

[Steve Shannon]

They can be connected in parallel or in series, but not both simultaneously. Using a 24 volt charger allows you to pull 24 volts, or 12 volts from either battery.
Some wheelchair users install a plug made of Anderson Powerpoles that can be unplugged and replaced with another plug. By doing this you can, by changing the plugs, choose between two batteries in parallel and two batteries in series. They do that so they can tie their batteries into their vehicle electrical system to charge their batteries or to start their vehicle if they have problems with the vehicle battery.

 

[tsmith1315]

Is this an automobile, charging by alternator?

 

[OverTheTop]

Perhaps go with a 12V system and a boost converter to take it up to 24v where needed. How much current you need on 24v?

 

[HyperSpeed]

Perhaps go with a 12V system and a boost converter to take it up to 24v where needed. How much current you need on 24v?

If I conservatively estimate the max amperage to ever be given to 24v devices, it would be under 30A, most likely around 15A until I install the twin baja-style lights I machined w/ 12x Cree XHP-50.3 LEDs in each light head (24x total emitters). I'm actually using twin boost drivers within each head, 4x total. It's the light bars I'm mounting first that accept 24V. It's a Polaris Ranger 1000. I already had the German boost drivers for the custom lights, so maybei should consider removing the factory light bar drivers and installing one powerful driver or two the LED strings could run directly from. Interesting idea, wasn't sure about the setup but aftermarket boost drivers do sound like a good idea. Thanks

 

[HyperSpeed]

Here's an additional thought I think I should mention; I've found the, "600W, 800W, 1200W" etc, boost-converters on places like ebay. I have no trouble finding boost drivers with ample power overhead, in other words.

Normally, it wouldn't make sense to drive a driver with another driver--due to excess efficiency losses stacking up. But herein lies the issue pertaining to my situation. What follows may contain some details that may not seem pertinent, but I will describe what's going on so everything at least makes sense. The boost-converters I already have, which were chosen due to their USB programmability and PWM/dimming functions (I gain precise LED control methods and temp-sensing protection features by using them), are essentially here to stay--they're already integrated (reflow soldered) onto each light-head's solid copper internal and threaded-in heat-sink.

Since those boost drivers are currently there to stay, this brings up a question. If those drivers are fed 12V input, they won't be able to push the 12x LEDs to high enough current, due to incoming current limitations. However, if they are fed 24V-36V for example, they can produce a much higher output wattage total.

My question then becomes; if I go with a high-wattage boost-converter that's easily capable of taking 12V @ 20A and turning it into an output of 36V @ ~6A or so, can I safely power the smaller boost-converters with the output from the larger boost converters? I understand it's probably not typical to do this, and will have decreased overall efficiency, but I will gain the use of features that made the existing German boost converters desirable to use. Would this type of boost-driver-powering-boost-driver setup have any inherent operational concerns I should watch out for? Thanks

 

[OverTheTop]

Just watch out for the maximum voltage allowed on your boost converter inputs. Don't exceed that. Not sure if the converters you have a buck-boost or just boost. Buck is about lowering voltage, boost about increasing it. It depends on the design of the units on your LED lights. You may gain some efficiency at the LED regulators by feeding them a higher voltage. Either way you are getting a boost converter somewhere along the way so will likely take an efficiency hit. It is just a matter of where that inefficiency shows up, as it contributes heat that needs to be dissipated.

 

[OzHybrid]

deleted.

 

[David Schwantz]

It is called a series/parallel switch. They are used in trucks that have a 12v system but need 24 v starters.

 

[OzHybrid]

The Chinese converters are woefully overspecified compared to their real-world performance. Divide their spec by 3 for cool operation or 2 if you're OK with hot and be careful to ensure you keep it cool. ie don't put it in a sealed box and get it hot enough to fry an egg on. Egg frying temperature is bad for electronics. Silicon semiconductors have a max temp of 150 deg C. That's the internal semiconductor junction temp. Not the external temp of the casing.
151 deg = dead semi