Question for combo solar gawds/RC (remote control) enthusiasts

[Mike Jordan]

I have been searching the interwebs for a good solar charging solution for the odd voltages of 4s and 5s 18650 Li-Ion packs. Suddenly I had an epiphany... or a very bad idea. Thats where a solar gawd/RC enthusiast would help

I have a 120w portable panel. The manufacturer rates the Voc at 19v. I measured it at 19.9v cloudy, 22.7v sunny.

I have an iCharger 206b (link for specs) which will charge my batts connected to a power supply rated 10-28v.

Can I connect my iCharger 206b to my solar panel, to crate a solar charge controller, to charge my batts?

 

[mandrews44]

I believe you will encounter issues with the charger's incoming voltage / current monitoring. If it asks for more power than the panels are providing at any given time, it will throw an errors. If you can program it to never ask for more power than is being supplied, yes.. Otherwise, you will need a battery connected to the charger that will supply any surges it is momentarily asking for. On the other hand, if a cloud passes, that charger will shut down and throw an error. You might get away with 4S but 5S will probably not work because it will require a steady supply > 21 volts. Open voltage on a solar panel is not the same under heavy load. You will be pushing your luck with 5S due to the voltage drop that can and will happen frequently with clouds. If you used a boost converter to take the panel voltage and always output 28 volts, you will have better luck but not total success. You will also lose 5-15% of your power in the boost converter. To do this where you do not have to restart it every time a cloud passes by, you would need a small solar charger,24v battery and a boost converter (variable to 28v) to charge both 4s and 5s..

 

[Mike Jordan]

I believe you will encounter issues with the charger's incoming voltage / current monitoring. If it asks for more power than the panels are providing at any given time, it will throw an errors. If you can program it to never ask for more power than is being supplied, yes.. Otherwise, you will need a battery connected to the charger that will supply any surges it is momentarily asking for. On the other hand, if a cloud passes, that charger will shut down and throw an error. You might get away with 4S but 5S will probably not work because it will require a steady supply > 21 volts. Open voltage on a solar panel is not the same under heavy load. You will be pushing your luck with 5S due to the voltage drop that can and will happen frequently with clouds. If you used a boost converter to take the panel voltage and always output 28 volts, you will have better luck but not total success. You will also lose 5-15% of your power in the boost converter. To do this where you do not have to restart it every time a cloud passes by, you would need a small solar charger,24v battery and a boost converter (variable to 28v) to charge both 4s and 5s..

Good points. This charger is highly programable with more features than I have ever used. I'll have to look for some incoming power settings. The wall plug power supply I use for the charger says it outputs 13.5-18v. There are no controls on the power supply. I've never measured to see if, or how it varies.

I might have to give this solar charger hook up a try, with some close monitoring

 

[HRTKD]

My RC days are gone. I gave away my truggies and all that came with it, probably a couple hundred dollars in spare parts too.

If it was me, I would look at using a programmable solar charge controller (SCC) that can span the voltages you're looking to charge. The Victron SCC is auto-sensing at 12/24v so maybe that won't work. But if you plug in a 19v battery, maybe it would think it's 24v. Through setting the parameters you may be able to get the exact charge profile you need for your battery. I don't KNOW that this will work. The parameter range of the Victron may not cover your battery voltage.

 

[Mike Jordan]

My RC days are gone. I gave away my truggies and all that came with it, probably a couple hundred dollars in spare parts too.

If it was me, I would look at using a programmable solar charge controller (SCC) that can span the voltages you're looking to charge. The Victron SCC is auto-sensing at 12/24v so maybe that won't work. But if you plug in a 19v battery, maybe it would think it's 24v. Through setting the parameters you may be able to get the exact charge profile you need for your battery. I don't KNOW that this will work. The parameter range of the Victron may not cover your battery voltage.

The Victron will work. But Looking for a more cost conscious controller, as this will be just a small DIY power station

 

[Sverige]

I have four ichargers and have used them since they first came out, so it’s a unit I know fairly well (and rate highly). Your main issue is it‘s designed to provide a fixed output current. This means the icharger cannot react to the solar panel’s power delivery varying below the level at which the icharger is demanding. I reckon it could work in good sunny conditions, if you select the charge current to be within the panel’s capabilities, but will be an unreliable kind of arrangement because the first cloud which comes along might trip the input low voltage disconnect.

I believe the icharger should deal ok with the fact the input voltage is varying, as at heart it’s essentially a synchronous power converter which will give you a fixed output regardless of where the input voltage is at (within the accepted 10-28V range).

Your main issues are:
- it‘s really inefficient, as you need to choose a charging current which keeps the icharger demanding less power than the panel could provide. That output power keeps rising through the charge profile as the 18650 cell voltages rise, so you must actually begin your charge with much less power than the panel could actually be giving you. Plus you’ll have an error margin as you can’t expect to guess just right, so overall you’re just wasting a whole load of power which an MPPT controller would have been delivering to your battery.
- it’s unreliable, as one small drop in panel illumination could cause the panel voltage to drop too low, because the icharger will actually drag it down there as it pulls more and more current if the panel voltage begins to tail off. Your icharger is not going to react to less power being available and reduce the charging current (as a SCC would). It’s going to keep pulling and trip with a low voltage error.

So how much less power than your panel could produce do you want to accept using, and how much fussing over it and restarting it each time it fails do you want to do?

I would look into some of the cheap mppt modules which @rin67630 can probably tell you more about. Some of those must have adjustable output voltage which would suit your 4S and 5S Li-Ion packs? What kind of charging current do you want to deliver to your packs anyway?

 

[rin67630]

I have been searching the interwebs for a good solar charging solution for the odd voltages of 4s and 5s 18650 Li-Ion packs. Suddenly I had an epiphany... or a very bad idea. Thats where a solar gawd/RC enthusiast would help

I have a 120w portable panel. The manufacturer rates the Voc at 19v. I measured it at 19.9v cloudy, 22.7v sunny.

I have an iCharger 206b (link for specs) which will charge my batts connected to a power supply rated 10-28v.

Can I connect my iCharger 206b to my solar panel, to crate a solar charge controller, to charge my batts?

View attachment 32162

If i read "Wide input voltage" you should be able do go for it in confidence. Worst case it would not be the last optimum, but it would surely work quite well. Measure your panel voltage with bright sun and full battery load. if it is something between 16V and 18V you won!

 

[Sverige]

Well it seems like some of what I said above was completely wrong, because a feature of the icharger I’ve never needed to use - input current limit - seems like it will prevent the charger dragging your panel volts down, and someone has already successfully used the icharger as a pseudo-MPPT charger, by changing the inout current limit to get the solar panel into its happy place.

I still think this would only work reliably on a cloudless day.

 

[mandrews44]

I still think a small (5amp) boost converter set to 28 volts connected to a 15ah LiFePo4 24v battery is the best way to go. It will remove the issue with cloudy days and provide enough voltage for the 5S to charge. The BMS on the battery will handle up to 29.2v but you don't need to top off the battery, just keep it charged enough to handle clouds and keep it within the range of the charger.

Not knowing the size of the batteries being charged is a problem though. When I was using those batteries when I first got into drones, they were 5.5ah batteries each and I had 4 of them. A 120 watt solar panel would not keep up with my large copter with 4 300 watt motors and only 10 minute flying time per battery. A SCC isn't really necessary with LPF because the only charge cycle is 14.6v (29.2v for 24v) until the BMS shuts off the charge. My first portable solar generator I build using only a 24v to 14.6v adjustable buck converter and 2 Lifepo4 batteries totaling 20ah with a 50 watt panel. That buck converter worked as well as any MPPT back then and cost $10 vs hundreds.

Here is a battery I would use.. This is NOT an affiliate link..
12V 20Ah Deep Cycle LiFePO4
Selling for $65.99, best I've ever seen. I use this brand in my UPS, (6 ah version).

 

[mandrews44]

Once I converted to LiFePo4, I won't use SLA's again. They may be cheaper but their cycle life is very low. My cable company used them and I have had to replace them every year or so and that is for backup / storage, not cycle use. When I have to replace it again, it's getting a LiFePo4. I first started with a Gel battery bank for my house solar (off grid type) and they also bit the dust in under a year with very careful, automated, monitoring and logging. For long term and cycle usage, LPF is the only way for me. LPF is lighter weight, higher energy density and 20 times the cycle life. While initial cost is higher, the cost over 10 years is $0 vs replacing the battery every year or 2.

It's a good idea for initial testing.

 

[Sverige]

I still think a small (5amp) boost converter set to 28 volts connected to a 15ah LiFePo4 24v battery is the best way to go. It will remove the issue with cloudy days and provide enough voltage for the 5S to charge. The BMS on the battery will handle up to 29.2v but you don't need to top off the battery, just keep it charged enough to handle clouds and keep it within the range of the charger.

Not knowing the size of the batteries being charged is a problem though. When I was using those batteries when I first got into drones, they were 5.5ah batteries each and I had 4 of them. A 120 watt solar panel would not keep up with my large copter with 4 300 watt motors and only 10 minute flying time per battery. A SCC isn't really necessary with LPF because the only charge cycle is 14.6v (29.2v for 24v) until the BMS shuts off the charge. My first portable solar generator I build using only a 24v to 14.6v adjustable buck converter and 2 Lifepo4 batteries totaling 20ah with a 50 watt panel. That buck converter worked as well as any MPPT back then and cost $10 vs hundreds.

Here is a battery I would use.. This is NOT an affiliate link..
12V 20Ah Deep Cycle LiFePO4
Selling for $65.99, best I've ever seen. I use this brand in my UPS, (6 ah version).

When using a boost controller, do you need to choose one rated for the full Voc of the solar panel (or panel array), or can you rely on the boost controller dragging that panel voltage down to within its range? For example, 12V nominal solar panels might have a Voc of 18V, so a 2S arrangement at up to 36V max might not suit a boost controller with a 32V inout ceiling. Or maybe it would be ok, if the boost controller is bringing the input voltage down a bit by sucking current from the solar panels?

 

[Mike Jordan]

Well it seems like some of what I said above was completely wrong, because a feature of the icharger I’ve never needed to use - input current limit - seems like it will prevent the charger dragging your panel volts down, and someone has already successfully used the icharger as a pseudo-MPPT charger, by changing the inout current limit to get the solar panel into its happy place.

I still think this would only work reliably on a cloudless day.

DAYUM!

THANKS for that link! I never thought to search RC groups. I am going to see if I can make this work.

 

[Mike Jordan]

I still think a small (5amp) boost converter set to 28 volts connected to a 15ah LiFePo4 24v battery is the best way to go. It will remove the issue with cloudy days and provide enough voltage for the 5S to charge. The BMS on the battery will handle up to 29.2v but you don't need to top off the battery, just keep it charged enough to handle clouds and keep it within the range of the charger.

Not knowing the size of the batteries being charged is a problem though. When I was using those batteries when I first got into drones, they were 5.5ah batteries each and I had 4 of them. A 120 watt solar panel would not keep up with my large copter with 4 300 watt motors and only 10 minute flying time per battery. A SCC isn't really necessary with LPF because the only charge cycle is 14.6v (29.2v for 24v) until the BMS shuts off the charge. My first portable solar generator I build using only a 24v to 14.6v adjustable buck converter and 2 Lifepo4 batteries totaling 20ah with a 50 watt panel. That buck converter worked as well as any MPPT back then and cost $10 vs hundreds.

Here is a battery I would use.. This is NOT an affiliate link..
12V 20Ah Deep Cycle LiFePO4
Selling for $65.99, best I've ever seen. I use this brand in my UPS, (6 ah version).

I have considered that route. It would sure be easier to follow the path of least resistance (no electrical terms implied ) I may end up there anyway. But crafting a DIY solution from stuff I already have, is more fun, than just making it work like everyone else does

 

[mandrews44]

Rule #1, there is no such thing as a perfect solution. Every solution creates a new set of problems and as long as the solution only creates problems that can be lived with, your solution is perfect..

 

[HaldorEE]

My RC days are gone. I gave away my truggies and all that came with it, probably a couple hundred dollars in spare parts too.

If it was me, I would look at using a programmable solar charge controller (SCC) that can span the voltages you're looking to charge. The Victron SCC is auto-sensing at 12/24v so maybe that won't work. But if you plug in a 19v battery, maybe it would think it's 24v. Through setting the parameters you may be able to get the exact charge profile you need for your battery. I don't KNOW that this will work. The parameter range of the Victron may not cover your battery voltage.

The auto select only happens the first time you power it up.

From the Victron MPPT SmartSolar manual.

"The Absorption voltage, Absorption time, Float voltage, Equalisation voltage and Temperature compensation settings are all configured to a preset value - but can be user-defined.

User-defined presets will be stored in the preset library - in this way installers will not have to define all the values each time they are configuring a new installation."

4. Settings

www.victronenergy.com

I haven't used this yet, but if anybody is going to let you set things the way you want them, I would put my money on Victron. Should double check on their support forum. The question may have already been asked and answered.

 

[Mike Jordan]

The auto select only happens the first time you power it up.

From the Victron MPPT SmartSolar manual.

"The Absorption voltage, Absorption time, Float voltage, Equalisation voltage and Temperature compensation settings are all configured to a preset value - but can be user-defined.

User-defined presets will be stored in the preset library - in this way installers will not have to define all the values each time they are configuring a new installation."

4. Settings

www.victronenergy.com

I haven't used this yet, but if anybody is going to let you set things the way you want them, I would put my money on Victron. Should double check on their support forum. The question may have already been asked and answered.

Another member here set up 5s Li_Ion with a Victron SCC. So it works. Good instincts.

But I was trying to find another low, or no cost solution, as this may turn out to be something that does not see much use, and may never be more than a proof of concept