DC DC Converter for OUTPUT from LIFEPO battery

[Mark2457]

Hi All

I'm planning a small setup for my 4x4. need to be able to charge from alternator while driving and solar when stationary

• BattleBorn Heated LIFEPO battery (1 to start with)
• Renergy DC-DC On-Board Battery Charger with MPPT
• 2 x 100W solar panels (haven't selected brand yet)

I have no need for AC output, so don't need a sine wave inverter. What I do need is regulated 12v (for Dometic Fridge) and several USB's for tablet, phone, etc.

Anyone got a recommendation?

Thanks

Mark

 

[DiploStrat]

Why would you not simply wire the refrigerator to the battery? What is the problem you are trying to solve?

 

[ScottPC]

Wiring the fridge to the battery will entail a switch and a fuse, no other regulation is needed. If you have several other devices perhaps a DC fuse panel would make for a cleaner install. The lithium battery will provide a very steady (i.e flat) voltage.

 

[DaveInDenver]

The only reason I can see is if the battery didn't happen to have a compatible chemistry or management system and was thus unregulated with an excessively high voltage. But that won't be the case with a LiFePO4 Battle Born. You will need a 12V-5V USB adapter, though.

 

[shinyblackdeer]

There are much cheaper options, of course, but something like this would be an easy solve: Blue Sea all-in-one.

 

[john61ct]

99.9% load devices designated "12V" nominal

can handle a much wider voltage range than you will ever see on your battery output

 

[ScottPC]

Wiring the fridge to the battery will entail a switch and a fuse, no other regulation is needed. If you have several other devices perhaps a DC fuse panel would make for a cleaner install. The lithium battery will provide a very steady (i.e flat) voltage.

If the Renogy doesn't have this functionality, you may want to get the victron wireless shunt that will connect via Blue tooth to your phone which will allow you to monitor voltage, current in, current out and the state of charge. This a cheaper alternative to the victron bmv 712 which has been really popular.

 

[jonyjoe101]

On my lifepo4 220ah (not battleborn) it had problems powering my 26L joytutu 12 volt compressor fridge, this fridge is very sensitive to voltage drop when the compresser starts. I moved the low voltage cutoff button on the fridge from low to high which didnt fix the problem. I also tried it with a 312ah li-ion battery pack and it also had the same problem , the fridge compressor would stop running and then cycle back and forth trying to start. This usually only occur at night time when the battery was no longer being charged by solar and the battery was at 50 percent or less.

Some 12 volt fridges probably have this similar problem, and buying a "better" fridge isnt an option. The way to fix it is with a 12 volt dc to dc boost/buck converter. You have to build your own, a boost or a buck by itself won't work. You set the boost output to 19 volts and then it goes into into the buck which is set to 13.2 volts (6 amps) output (I tried differfent output voltages but 13.2 volts was the lowest were the fridge work the best). This fixed my problem, I havent had any more compresser shutting down since I started using this converter. On my li-ion battery pack it runs the fridge even when the voltage on the pack reaches 10 volts. I have been using this converter non-stop 24/7 since dec 2020 to power my fridge, power use on the converter is inconsequential (less then 50ma)

Picture of boost/buck converter I built as a low amp battery charger but I repurpose to power my fridge.

 

[john61ct]

Yes a boost converter is appropriate to compensate for poor design of load devices.

They really should tolerate transient drops from high current demand down to 10V, say 11V for continuous operation

a soft start unit helps too, especially with very high loads like aircon.

But do not expect such infrastructure to reduce the Ah capacity needed to support such high consumption loads, even if only used for short times per 24 hours.

LI banks "can" support 3C loads (cell based, drop-ins usually far lower)

but it's not usually a good idea to base your design on that.

For lead banks, well below 1C is OK for AGM, half that best, especially for FLA.

 

[Mark2457]

On my lifepo4 220ah (not battleborn) it had problems powering my 26L joytutu 12 volt compressor fridge, this fridge is very sensitive to voltage drop when the compresser starts. I moved the low voltage cutoff button on the fridge from low to high which didnt fix the problem. I also tried it with a 312ah li-ion battery pack and it also had the same problem , the fridge compressor would stop running and then cycle back and forth trying to start. This usually only occur at night time when the battery was no longer being charged by solar and the battery was at 50 percent or less.

Some 12 volt fridges probably have this similar problem, and buying a "better" fridge isnt an option. The way to fix it is with a 12 volt dc to dc boost/buck converter. You have to build your own, a boost or a buck by itself won't work. You set the boost output to 19 volts and then it goes into into the buck which is set to 13.2 volts (6 amps) output (I tried differfent output voltages but 13.2 volts was the lowest were the fridge work the best). This fixed my problem, I havent had any more compresser shutting down since I started using this converter. On my li-ion battery pack it runs the fridge even when the voltage on the pack reaches 10 volts. I have been using this converter non-stop 24/7 since dec 2020 to power my fridge, power use on the converter is inconsequential (less then 50ma)

Picture of boost/buck converter I built as a low amp battery charger but I repurpose to power my fridge.

View attachment 664766

Thanks for info. Where can I find plans for something like that


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[Mark2457]

Wiring the fridge to the battery will entail a switch and a fuse, no other regulation is needed. If you have several other devices perhaps a DC fuse panel would make for a cleaner install. The lithium battery will provide a very steady (i.e flat) voltage.

Thanks. Yes I plan on installing a fuse panel and then several hardwired outputs (12v and USB)

Reviews I’ve watched about battery packs like jackery seem to make big deal about having a regulated 12v output.


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[vomhorizon]

Your Battle Born will still be at or above 12 volts even when it is down to 8-9% state of charge (and you don't really want to dip below 12 v for battery health anyway) and as is, your refrigerator should have a low voltage cut-off which you can also set. Pick up a shunt so that you can monitor SoC as doing so with voltage is difficult for LiFEPo4. I run a Battle Born, Renogy DC-DC (though I chose the simple system Renogy DC-DC because with it, I could set the charge voltage to exactly 14.6 which the BB prefers) and solar panels. As others have advised, get a fuze block, run correct fuses and make sure your connectors are well crimped (I use powerpole and SB50 connectors to connect my system to accessories). One of the most surprising things I noticed when moving from AGM to Lithium was the voltage stays nearly constant in the 13 volt band throughout most of the cycle. I could be down to 20% SoC and still be at 12.8 volts which is what my AGM would have been at full charge. Only when you go into the low single digit percentage SOC do you begin to see it move more dramatically.

 

[DaveInDenver]

Reviews I’ve watched about battery packs like jackery seem to make big deal about having a regulated 12v output.

Those portable power boxes use lithium batteries that aren't necessarily directly compatible with things designed to plug into 12V vehicle stuff. I'm pretty sure Jackery is using lithium-ion cells to make up a battery which will either be too low (around 11V) or too high (around 15V) to use without a regulator to make a normal 12V output.

Most likely they actually use a very high voltage pack, probably 6S with a pack voltage of around 25V since their main concern is charging from a solar panel and generating the 120VAC inverter output. Regulating down from 25V to 12V or 5V is basically trivial.

The 12V in this case is going to be well regulated, meaning it'll always be pretty much exactly 12V as a result of this conversion. But your fridge or other things designed to use in a car don't need exactly 12V. They'll work from over a range of voltages around 12V within a volt or two, so very tight regulation isn't really critical.

A drop-in replacement like a Battle Born isn't quite the same thing as a Jackery pack. A battery built with LiFePO4 (LFP) cells can be closer to the range of a 12V lead acid and almost be used without a regulator but they'll still use a battery management system for protection and compatibility to make them "drop in" without issues. Their output could still be called regulated but it's not quite the same thing.

 

[Mark2457]

Those portable power boxes use lithium batteries that aren't necessarily directly compatible with things designed to plug into 12V vehicle stuff. I'm pretty sure Jackery is using lithium-ion cells to make up a battery which will either be too low (around 11V) or too high (around 15V) to use without a regulator to make a normal 12V output.

Most likely they actually use a very high voltage pack, probably 6S with a pack voltage of around 25V since their main concern is charging from a solar panel and generating the 120VAC inverter output. Regulating down from 25V to 12V or 5V is basically trivial.

The 12V in this case is going to be well regulated, meaning it'll always be pretty much exactly 12V as a result of this conversion. But your fridge or other things designed to use in a car don't need exactly 12V. They'll work from over a range of voltages around 12V within a volt or two, so very tight regulation isn't really critical.

A drop-in replacement like a Battle Born isn't quite the same thing as a Jackery pack. A battery built with LiFePO4 (LFP) cells can be closer to the range of a 12V lead acid and almost be used without a regulator but they'll still use a battery management system for protection and compatibility to make them "drop in" without issues. Their output could still be called regulated but it's not quite the same thing.

Awesome info thanks.

Still Stuck in the usb side. Want type c, quick charge and type a, but don’t want a bunch of usb converters hanging out


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[ScottPC]

Awesome info thanks.

Still Stuck in the usb side. Want type c, quick charge and type a, but don’t want a bunch of usb converters hanging out


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Maybe just go with the standard 12V cigarette style outlet? There are plenty of devices/adapters that can be found on amazon that use this connection for the various USB types. The cig style has remained constant for years so it's a good choice, imo.