Another secondary 12v system thread

[MAAZcruiser]

Read quite a few threads on the subject but I’m running into some trouble. Trying to set up a third 12v battery for stereo and probably some other accessories down the line.

I have a 12v converter that came with the truck as well as a solar charge controller that I picked up that I’m hoping to use to charge a small AGM battery.

I have the 12v converter wired to a keyed relay then hooked up to the charge controllers solar panel connection and the battery hooked up to the battery connection on the charge controller. The problem is 12v starts to over heat pretty quickly when hooked up to the system. Fuse doesn’t blow but gets wicked hot and can smell it over heating. Works fine on its own.

here’s the list of components I’m using. Any help is appreciated. I’ll try and put together a diagram of my wiring

12 v converter

Solar charge controller

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[Earwigg]

What's overheating?
The description for the solar charge controller says to only connect solar panels to it nothing else.
What are you planning to run off the battery?
I have a converter which is always on with a head unit wired off that the 4wd button turns the head unit on and off via the acc wire. It will happily run for 6+hours.

 

[MAAZcruiser]

What's overheating?
The description for the solar charge controller says to only connect solar panels to it nothing else.
What are you planning to run off the battery?
I have a converter which is always on with a head unit wired off that the 4wd button turns the head unit on and off via the acc wire. It will happily run for 6+hours.

It’s the 12v converter that overheats.
Worried about the 12v converter draining the battery over time if it’s always on.
probably run a fridge at some point and I’d just like to have the option of running 12v accessories.
trying to do something like this

Charging a third 12v battery from 24v?

I run a 2H with the 24v setup. Previously i've run all my 12v accessories and gadgets from a 24/12v converter, but as the accessories stack up, and the need to be able to use some accessories while camping and so on, i want to run everything via a third battery, getting charged only when the...

forum.ih8mud.com

 

[Earwigg]

Take the converter out of the system. The solar unit will convert the 24v to 12v and charge your batterys. A relay or a switch between you battery's and the solar charger might be a good idea.

 

[daboheme]

The 12V converter is overheating because it is likely a linear converter running at it's maximum current limit (likely more than the rated 1A). Let's assume a 2A current limit (ie fully charging the battery). Engine running, input voltage would be about 28V. Regulated output is 14V so voltage drop is also 14V. Multiply this by 2A and the converter must dissipate 28W of power. This is a fair amount without convection cooling. Maybe add a small fan?

I would be weary of connecting the 24V of the vehicle to the solar charge input. These are normally power limited inputs and your batteries and alternator can typically supply a fair amount more than what the solar charge controller was intended for (ie a couple of kWs versus a couple of 100s of watts). I speak from experience have blown some charge controllers...

Your best bet is to find a cheap adjustable switch mode power supply (ie DC-DC converter) rated at about 10-20% of the capacity of the battery. This is what I currently use for a 12V/200Ah lead crystal battery. Something like the SD-150 series from Meanwell.

 

[MAAZcruiser]

Your best bet is to find a cheap adjustable switch mode power supply (ie DC-DC converter) rated at about 10-20% of the capacity of the battery. This is what I currently use for a 12V/200Ah lead crystal battery. Something like the SD-150 series from Meanwell.

with something like this isn’t there potential to over charge the battery if the truck is running for a long period of time? or are you saying use that along with the solar charge controller?

 

[daboheme]

Use just the SMPS. Set the output voltage of the SMPS to 13.6V-13.8V output voltage with no load. You can then connect the SMPS directly to the battery. The SMPS will current limit at it's maximum rating until it reaches the set voltage. Current will then drop once the set output voltage is reached and voltage will be maintained at the set output voltage as battery is effectively being float charged. I use the Meanwell brand extensively as both DC-DC charger for my 12V aux battery in 24V Landruiser, as well as float chargers for batteries from household 220V input in general.

 

[MAAZcruiser]

Use just the SMPS. Set the output voltage of the SMPS to 13.6V-13.8V output voltage with no load. You can then connect the SMPS directly to the battery. The SMPS will current limit at it's maximum rating until it reaches the set voltage. Current will then drop once the set output voltage is reached and voltage will be maintained at the set output voltage as battery is effectively being float charged. I use the Meanwell brand extensively as both DC-DC charger for my 12V aux battery in 24V Landruiser, as well as float chargers for batteries from household 220V input in general.

My battery is pretty small. Only 21Ah. Could I use something like this and potentially upgrade my battery down the line?

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[daboheme]

I think it should be okay. The item to look out for in the datasheet is under "overload protection type". In the case of the SD150B it is "hiccup mode" and auto-recovers and current limits under overload. I use the RS-75-15 for floating my backup batteries from home supply. Also hiccup mode. I use the SD350B-12 (27.5A rated, up to 130% overload so actually 35A output current) to charge my 12V 200Ah aux battery from the 24V Landcruiser alternator supply. This one is trickier to manage since an overload conditions requires you to disconnect and reconnect the output. You can use the IGN signal to switch a relay to disconnect the input to the SMPS if required. The ones I've used have no problem with remaining connected to the battery with no voltage at the input.