I've got a solar charge controller and I've also got an old 19+v laptop charger. I've hooked up the laptop charger to the solar input on the solar charge controller and it seems to work to charge the battery. Is there any reason I shouldn't be doing this? Solar charge controller is design to accept variable voltage from the panels so I'm assuming a stable 19v won't hurt it, but I dont know for sure. Is my reasoning sound? Is anyone else doing this?
solar charge controller as a dc-dc charger?
- Thread starter trae
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dreadlocks
Well-known member
you can do it, but if it gets unplugged the solar charger will continue to draw power from the battery, so its not a great solution for unattended maintenance..
If you had fixed panels and used a couple diodes to isolate em its workable.. if shore power is lost the fixed solar can keep things going.
If you had fixed panels and used a couple diodes to isolate em its workable.. if shore power is lost the fixed solar can keep things going.
Martinjmpr
Wiffleball Batter
Where is the 19v laptop charger drawing its power from? A 120vAC source? Or a 12v source with an inverter?
Also what kind of battery are you charging and what are you using said battery for?
Also what kind of battery are you charging and what are you using said battery for?
It's a 105Ah LiFePO4 system. Max charge is 1C. It's basically a portable battery that either goes in my truck, or in the trailer. Very low draw (12v fridge, some led lights, phone recharging).
The laptop charger is a 120v AC charger, but outputs 19v at 5amps.
@Verkstad, it is true that from empty it'll take 15+ hours (at best) to charge fully, but that's not an issue for me.
@dreadlocks at this point I have a manual switch that disconnects the solar charge controller.
dreadlocks
Well-known member
I'm sure you do, but the issue here that it is manual.. If you park your battery out back, plug it into shore power and then walk away.. who's gonna manually flip that switch when the charger gets inadvertently unplugged? A Normal Battery maintainer will simply stop maintaining the battery if power is lost, this setup will actively drain your battery entirely until its completely toast in such a failure mode.. its a very poor design for unattended charging unless you added some sort of AC relay that required external power for the solar charger to be connected to the battery bank.
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Ahh, I see what you're saying. The storage charging is something I have not figured out. I have no need to maintain 100% state of charge, unless that is somehow not good for the cells. I intend to manually charge the pack before I leave on a trip, then stick the pack in storage when we get home and top it off with solar while on the road. In other words, there will be no unattended charging.
dreadlocks
Well-known member
With LFP you discharge it to ~40% SOC and leave it sitting disconnected from everything.. also you should not be charging more than 0.4C if you want it to last.
As long as you don't ever leave it unattended it should be fine, I charge my LFP this way.. but Ive got it wired up to both a fixed solar panel on the roof and the shore charger at the same time so if I lose shore power it'll failover to the solar panel.
As long as you don't ever leave it unattended it should be fine, I charge my LFP this way.. but Ive got it wired up to both a fixed solar panel on the roof and the shore charger at the same time so if I lose shore power it'll failover to the solar panel.
Martinjmpr
Wiffleball Batter
OK I'm not quite understanding your setup. Post title is "solar charge controller as a dc-dc charger" and then you talk about having a laptop power supply with a 19v output.
Where is the 19v power supply drawing its power from? An AC source like a 120v AC house current?
If you have AC power, why not just use a standard 120v AC charger? No need to go through the solar controller, just attach directly to the battery to charge it up. There are even "smart chargers" that monitor your battery state to keep it at the right kind of charge (bulk, float, etc.)
Or are you saying that you don't WANT to have to buy another 120v AC charger and since you already have the laptop power supply that takes in 120v AC and puts out 19v, you want to run that 19v through a solar controller so it can regulate that down to the 13 - 14v you need to charge the LIFEPO battery?
Seems a bit Rube Goldberg-ish but I suppose it would work. How many amps is the 19v PS putting out?
Where is the 19v power supply drawing its power from? An AC source like a 120v AC house current?
If you have AC power, why not just use a standard 120v AC charger? No need to go through the solar controller, just attach directly to the battery to charge it up. There are even "smart chargers" that monitor your battery state to keep it at the right kind of charge (bulk, float, etc.)
Or are you saying that you don't WANT to have to buy another 120v AC charger and since you already have the laptop power supply that takes in 120v AC and puts out 19v, you want to run that 19v through a solar controller so it can regulate that down to the 13 - 14v you need to charge the LIFEPO battery?
Seems a bit Rube Goldberg-ish but I suppose it would work. How many amps is the 19v PS putting out?
Bingo. I have a 120v AC -19v dc at 5A laptop power supply. I dont think it's kosher to connect it directly to the battery because it's unlikely to know the LiFePO4 profile.
dreadlocks
Well-known member
I'm doing it because my Victron SmartSolar is more capable and programmable charger than any off the shelf AC charger at the charge rates I need..
DaveInDenver
Middle Income Semi-Redneck
A PWM solar controller can usually work as a DC-DC converter but be careful with MPPT controllers as they'll try and find the current limit of your power supply and exceed it. Whether this works or crowbars or blows a fuse will depend on the power supply.
dreadlocks
Well-known member
yeah MPPT can overload the psu if its undersized, once of the nice things about Victron SmartSolar is they have programmable current output to stay under your power supply.. if one were shopping for a power supply for this task on LFP I'd suggest shooting for a PSU that puts the controller right at the PSU peak efficiency.. usually that's about 80-90% load, good power supplies will list this in spec sheets.. so you'd try to oversize ~20% over the SC output.
If there's any chance both solar or shore power could be plugged in at same time, diodes to isolate em would be a good idea.
If there's any chance both solar or shore power could be plugged in at same time, diodes to isolate em would be a good idea.
Some controllers will not accept input from anything but panels.
Bit of a redneck engineering rig.
You are losing energy efficiency compared to a proper mains charger
but with mains, usually who cares?
Powering off a genset more important.
And at high amp rates this approach won't save money.
But otherwise, low and slow overnight charging, can be a cool kludge!
Bit of a redneck engineering rig.
You are losing energy efficiency compared to a proper mains charger
but with mains, usually who cares?
Powering off a genset more important.
And at high amp rates this approach won't save money.
But otherwise, low and slow overnight charging, can be a cool kludge!
This is a fine approach and your reasoning is sound.
One caveat is that your power supply must be rated for the current the charge controller will pull. You don't say what charge controller you have, but as mentioned with the Victron MPPT, you can set the charge current to be below your power supply limit. In this case, set it for 5A (at 13.6V, this is about 4A at 19V). Otherwise the charge controller will load down your power supply until the output voltage begins to crump and run it at its max output continuously.
Or if you want faster charging, buy a 24V output AC->DC power supply with a rating to match your charge controller. They are cheap:
One caveat is that your power supply must be rated for the current the charge controller will pull. You don't say what charge controller you have, but as mentioned with the Victron MPPT, you can set the charge current to be below your power supply limit. In this case, set it for 5A (at 13.6V, this is about 4A at 19V). Otherwise the charge controller will load down your power supply until the output voltage begins to crump and run it at its max output continuously.
Or if you want faster charging, buy a 24V output AC->DC power supply with a rating to match your charge controller. They are cheap:
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I don't think you want to use a PWM charge controller for this. In bulk mode, the PWM charger is just a wire and you are directly shorting your power supply to the battery. This will pull the 19V power supply down to 13.x V and max out the current, either causing the power supply to burn out or activate overload protection. With MPPT you can limit the current to be within the capabilities of the power supply.