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Dc/dc converter 12/24 - what to use it for?

IHaveThePower

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In the winter I was traveling across country and I needed a battery to run a diesel heater.
I also wanted a safe way to charge it from my trucks alternator. Being new to lithium I trusted the sales person but I'm thinking they messed up..

I bought a 100ah 12v bat and it worked great.

But the guy sold me a dc/dc converter that I now understand steps up the voltage rather than a straight up charger. He said it was a good unit to charge the battery from the alternator.
Was he right? Or was he wrong?
And now that I'm setting up a 24v system for a work trailer. Can I use this unit in any helpful way?

It's a victron - Orion 12/24 - 10a (240w) isolated dc-dc converter

It says In - 8-17v
And Out - 20-30v

I see this being quite useless in a system where my outback 150 MPPT CC with take the voltage and output 24v already.

It was also a little useless in the truck because I didn't think it was what I needed to draw the appropriate power from the battery.
I actually had the alternator blow up during that trip and had to replace it myself on the side of the road, mid winter. Which was a proud moment as I was just learning to work on the 7.3 e350 diesel truck.

Why does this unit exist?
How would someone make use of this in a practical way?

Cheers
 
Yes the new 24v battery can be charged with the 12v power supplied by the alternator though this DC-DC converter.
I assume the DC-DC converter is designed to be a battery charger. Some are just power supplies and will overload.
 
Yes the new 24v battery can be charged with the 12v power supplied by the alternator though this DC-DC converter.
I assume the DC-DC converter is designed to be a battery charger. Some are just power supplies and will overload.
It would have been useful if I had a 24v setup in the truck.

I guess I'll use it in my new setup if I need to charge the bank from a 12v source.
 
Yes the new 24v battery can be charged with the 12v power supplied by the alternator though this DC-DC converter.
I assume the DC-DC converter is designed to be a battery charger. Some are just power supplies and will overload.
He said it was a 12v battery
 
These are made to run a 24 volt appliance in your 12 volt vehicle, most have a wide range input voltage of 10-18 volts and a regulated 25.2 volt output. Many trucks, busses and airplanes are 24 volts. The radios from these can be powered by your converter (as it is properly called) A very similar device is a battery to battery charger, designed to charge a different chemistry or voltage battery from your vehicle. These are properly called B2B chargers, often used to charge a lithium battery from a vehicle. the two devices are very similar in circuitry but are “purpose designed” for the intended use.
 
So the reason you 'need' something like that to charge a lifepo4 from a vehicle charging system is that some people want to charge the lithium battery up to 14.6 volts (you don't have to and many people don't need to) but the lead acid charging system in the car will rarely if ever hit that voltage because it's too high for lead acid outside of some narrow conditions. So, you need a device to boost the voltage higher so you can feed it to the lithium battery.

You could hook the 24v output direct to the lithium battery, but what would happen in all likelihood is the converter would activate some kind of internal over-current protection over and over until it had finally spent enough time 'on' between overloads, to have charged the battery to its ~14.6v bms high voltage disconnect, at which point the voltage between the lifepo4 battery and converter would rise to ~25v. That would be the signal that it was 'fully charged'.

A better idea, in my opinion, is to hook the converter through a cheap solar charge controller to charge the battery. The charge controller will 'pulse' the power from the converter to the battery, which by itself does not improve the over-current problem with the converter, but it does allow you to select a different 'charge termination' voltage rather than relying on the BMS itself to protect the battery from overcharging. If you control the load on the battery through the load ports of the charge controller (either directly or through a relay) you can also select a different low-voltage cutoff point than the BMS's which is probably 10.0v. The advantage of this is that even though lifepo4 can be drained from 100-0% many times, it still lasts longer if you don't go all the way to 100 or 0. Setting it up to operate in something like a 90-20% range will make it last a bit longer. But an even more significant advantage is it allows you to keep a 'reserve' of energy in case you come back to find it has hit the low voltage disconnect, but you still need power to do something important like crank a generator or something like that.

I would recommend this unit because i own it and know for a fact that it has an adjustable current limit. What that does is let you set it to a current that won't overload your boost converter. PowMr pwm SCC with current limiting.
The current limit is not really necessary when you have a solar charge controller hooked to a solar panel array that is within the recommended range, but it's useful when using some other kind of charge source (like a boost converter or power supply) that doesn't have its own current limiting or does but really needs a lower limit for longevity. Just like the battery BMS, the converter might have internal protection circuitry, but sometimes those limits are set to avoid killing the thing instantly, not to ensure it has a long life. Operating something at 75% of its rating it will usually last much longer than at 100%. You can think of internal protections as like the rev limiter on a car's engine. Just because it will allow you to hit 7200rpm doesn't mean it won't last longer if you stop at 6500. I have used that exact controller with a 24v power supply to charge 12v lithium for a month or so before i transitioned to a larger all in one inverter/charger. In your scenario of hooking a 24v source to a 12v battery, it would be better to do it through this SCC than to NOT do it, in my opinion.

But i think what you will find regardless is that if you had an empty 100ah battery it would take 10hrs of driving to charge it to full with a 10a boost converter. I would consider it 'supplemental' charging at that current rate, unless you're just not using much of the 100ah capacity to begin with.
 
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