Cheap Single Cell Charger / LED Driver

[fechter]

I was waiting to prove your thing worked before sending the free panels, but this is proven and cheaper, and best of all I don't have to build it, so what voltage to you run again, so I know how many modules to send your way?
John

These things should work great up to their maximum rating of 35v. With a solar system, it should be possible to put these in series to make higher voltages. I'm not sure what the reverse drain (like you'd get at night) is. I can try to measure it. A diode may possibly be helpful.

I have a 12v standby power thing I'm working on. It will really be 4s li-ion, so more like 16.8V charging. I want to feed my cable modem and wireless router so I can still maybe get internet access during a power failure.

Pete: you're right about a lead-acid charger dropping its CV setting once the current gets below a certain point. This should essentially drop the charge current down to zero, at least for a while. With a timer or some other cutoff mechanism, you could just stop the charger. This would work about the same as the CC/CV board.

 

[auraslip]

I remember trying to use something like this for a bullet proof charging/balancing solution. Problem is the parts to isolate these so they can be powered by a single PSU quickly make the cost to high. Maybe a better option to investigate is dropping the voltage to what you need on $3 ebay 5v phone chargers.

 

[John in CR]

I'll send an extra module which will be perfect for your standby power thing. They were made for 4s laptop solar charges, so one should make for an efficient conversion.

I've been trying to dream up a simple solar balance charger and this seems to be just the ticket using 20 of my solar modules and 20 of these. I have modules that do about .3A into a 4s pack and larger ones that do about .6A into a 4s pack, so the home based solar balance charger will get into high enough current to need a heat sink on this charger/driver.

I love the flexibility these offer, because I can also go the other direction using one of these per solar module and build as little as 3 modules onto a bike to charge as high as 90V.

I'd still use a diode on each panel, so I hope that won't interfere with the charger's operation.

My one real concern is how these units will handle variances in voltage and current as the sun goes behind a cloud and comes back out. Will that stress the gadget, increasing failure rates? Will they come back on automatically as the sun comes out again?

 

[Pete1961]

Have measured several SLA chargers in use, typical: changeover point 44.5V, set back to 42V, Vbatt @ changeover point (charger disconnected) is actually only 40.2V
If charger left connected after changeover point, Vbatt will slowly rise, maybe to = 42V set back voltage. (not enough time to prove this just now) Does the changeover in SLA chargers detect voltage rise or current fall or indeed a mixture of both?
Seems to tell me that the CV limit setting for the module may need to be slightly higher than the desired final batt voltage (if the 1.9V per cell is a bare cell voltage value, not in charging circuit (may be different for NiZn). I guess if all is adjustable & closely monitored in the early days not too much can go wrong.

Have thought longer term of a 5A charger such as the Gaozhao 5A with trimmer pot, set up for Li ion - believe Li ion is just CC to a max voltage & then shut off. Back this up with a simple mech timer & either a heat sensor shut off or a probe digital stat with alarm (or both). Thus you have a charger that does not have to be built, nor has many open parts. Would though be specific to a pack A/h & V

 

[fechter]

If you were using one of these boards on a solar system, you will need a diode between the board and the battery to prevent draining the battery at night. If there is no input power, the battery will back feed the board and try to light up the LED. This drains about 10-20mA depending on the applied voltage. Alternately you could use a relay to disconnect from the pack at night. In a large system, you could possibly ignore the drain at night provided you didn't have any extended periods of dark or loss of input.

Cheap wall wart power supplies could run one of these, but I'm not sure if 5v is enough. It has an onboard LM7805 regulator that appears to power the op-amp and LEDs. 7V or more would be better. Since it's a buck regulator, if you used a higher voltage, it wouldn't need as much current. If you had a 12v, 1A wall wart, you might get close to 3A into a single cell output.

Pete:
I wish we made a separate thread for NiZn charging. I could possibly copy this thread to a new topic and edit.
Anyway, most lead-acid chargers change over when they sense the current has dropped below some point, usually around 100mA or 5% of the CC level. When it switches to float, the charge current will be zero at first since the battery is at a higher voltage than the charger. Eventually it equalizes and starts taking a little current. With most lithium chargers, when they sense the current has dropped to about the same level, they simply switch off and won't restart until the pack voltage drops by some amount.

 

[John in CR]

I don't know much about electronics, but I do always plan on diodes for any solar panel rig, whether the electronic device has one or not. What's the failure mode of a diode? ie as a short or open circuit? As long as they aren't overloaded, I hope they very rarely fail.

This has me really excited now with all the possibilities...even balance charging of my home based battery pack that can be LiFePo4 and Lipo, since I'll be able to so easily tune the top of charge cutoff.

 

[fechter]

Generally I've seen diodes short when they fail. If you pump enough current through it, it can sort of explode and go open.

 

[John in CR]

Generally I've seen diodes short when they fail. If you pump enough current through it, it can sort of explode and go open.

That tells me with lithium batteries I should go with 2 diodes in series just to be safe.

What about on/off cycling with intermittent sun?...Can low supply current or voltage be stressful for the units?

 

[fechter]

Diodes are pretty tough if you size them properly. Two diodes in series will dissipate twice the energy, so a single bigger one would be better.

I haven't tested them at low input, but generally the current would be so low that nothing would get hot. Otherwise I don't see why it would damage them. I've dialed them up and down with my bench power supply and that doesn't faze them.

 

[John in CR]

You're right. I'm sorry, I was thinking of the diode coming into play during charging and at high cost I want to avoid over-charging. The diode is just to stop back flow when the panels aren't producing, so I already would have double protection then...first the diode blocking, and second the reverse current would have to leak back through the device to power the panel with the battery. I will have per cell low voltage alarms that would wake the dead, and I'm a light sleeper when it comes to noises that are perceived risks, so I'm good with a healthy size single diode.

If you think about it, next time you're playing around with one, it's not so much just the variable input I'm interested in, but more what happens with it drops below the voltage and/or current supply thresholds. Is that stressful, especially when the cutoff may not be but say the sun comes back out from behind a cloud around midday and the unit gets hit with max current and voltage. Then a few seconds later a small band of cloud gets in the say followed with another max supply side hit. Am I just over analyzing it, and electronics are used to that kind of stuff at thousands of times per second? While that's probably a "yes", I would still never cycle the on/off switch of any of my plug into the wall chargers like that.

 

[RLT]

I just ran across these for $11 each:

5A Constant Current/Voltage LED Driver Battery Charging Module Voltmeter

• Module Properties: non-isolated constant current and voltage module
• Rectification: non-synchronous rectification
• Input voltage: 5V-32V
• Output voltage: 0.8V-30V
• Output current: adjustable maximum 5A
• Conversion efficiency: 95% (the highest)
• Switching frequency: 300KHz
• Output ripple: 50mV (max) 20M bandwidth
• Load Regulation: ± 0.5%
• Voltage Regulation: ± 2.5%
• Operating Temperature: -40℃to +85℃

Voltmeter Ammeter
• Measurement accuracy: 0.1%
• Refresh rate: about 200ms / times
• Display: 0.28"digital tube
• Current Range: 0A-5A
• Voltage range: 5V-30V
• Display Color Red

COMUNICATION PROTOCOL INSTRUCTION
• This module can communicate with computer,so that the current and voltage reading can be displayed by the computer.
• Because the output of this module is a TTL level,inorde to communicate with computer, thid=s level signal has to be transfered to a RS232 level which can recognize by the computer.

BAUD RATE: 9600 Bps
• BB CC ADDR 00 XX XX CRC (current return conmmound)
• BB CC ADDR 01 XX XX CRC (Voltage return conmmound)

Among it:
• BB CC is the Frame Header(2 bit)
• ADDR is the address of the module(1 bit)
• 00 is the command of current reading (1 bit)
• 01 is the command of Voltage reading(1 bit)
• XX XX random value (2 bit)
• CRC CRC verification

http://www.ebay.com/itm/5A-Constant-Current-Voltage-LED-Driver-Battery-Charging-Module-Voltmeter-/351082193864

I don't quite understand that computer connection stuff.. I know what most of the words and acronyms mean, but not how to implement it.... But I guess you don't need the computer stuff to make it work.

Am ordering one, but what do you guys think? Any use on this particular topic?

 

[CroArcher]

http://pages.ebay.com/link/?nav=item.view&id=400544557141&globalID=EBAY-US
Works fine..

 

[fechter]

That looks great. The RS232 link wouldn't serve any use to me, but you could use it to monitor the voltage and current remotely. It's amazing they can make these things so cheap.

 

[Matt Gruber]

just ordered 1 to try out. $2.15 free ship
http://www.ebay.com/itm/1pc-DC-DC-LM2596-Step-down-Adjustable-Power-Supply-Module-CC-CV-LED-Driver-New-f-/121411761288?pt=LH_DefaultDomain_0&hash=item1c44b47488
could use my 18v makita/dewalt packs to power my modem/tv, even my stereo, in an outage.
and 5 of these, at 1.12 each i can burn 1 up to test!
http://www.ebay.com/itm/5-pcs-DC-DC-LM2596-Power-Supply-Step-Down-Adjustable-Converter-Module1-5V-33V/130984321712?_trksid=p2047675.c100010.m2109&_trkparms=aid%3D555012%26algo%3DPW.MBE%26ao%3D1%26asc%3D24193%26meid%3D7145c8fd3aab48e6b726354496c8ea8e%26pid%3D100010%26prg%3D10284%26rk%3D5%26rkt%3D24%26sd%3D201084486537

 

[Matt Gruber]

regs came in. my 1st test was to hook up a 4" emergency fan. works good, and only $1.12.
i set the 12v fan to run slow so it is nearly silent, but still gives a nice breeze. draws 120ma at 4v, while the 12v source is only using 50ma. well worth 50ma for a fan during a power failure. i may use it other times too! I tried a 12" fan, but it was too noisey, and was 1.15a at 4v.
Next i'll use another reg to drop my 2p5s makita/dewalt bike packs down to 13v for the modem and HDTV. That will be used in the event that my 5 yr old car battery fails, which, is only a matter of time.
these 1.12 regs have a 50v input cap!

 

[fechter]

The switcher chip is rated for 35v, but some references say you can go over that as long as the differential between input and output stays below 35v. In most cases the load will be zero when you apply power, so not sure how you could get it going withoug blowing it up at higher voltages.

I want to use one to power my modem and wireless router too. I'm looking around for a good battery. In a power failure, I might still be able to use my laptop that way.

 

[John in CR]

I want to use one to power my modem and wireless router too. I'm looking around for a good battery. In a power failure, I might still be able to use my laptop that way.

Do those kinds of electronics typically need exact voltages or would 4s of LiFePo4 be close enough for one that says 12VDC at the input?

 

[fechter]

I want to use one to power my modem and wireless router too. I'm looking around for a good battery. In a power failure, I might still be able to use my laptop that way.

Do those kinds of electronics typically need exact voltages or would 4s of LiFePo4 be close enough for one that says 12VDC at the input?

I'm not exactly sure. I suppose it might vary from one unit to another. In general, I'd think it has a voltage regulator inside that drops it to 5v, so a wide variation on the input might be OK. Most of them have pretty crude wall warts to start with.