how would i charge my lifepo4 using solar?

Hi all,

Currently i do not have any solar panels but was thinking of getting some. I am not interested in performance as much as i am interested in an emergency backup or experiment. I wouldn't care how long it would take to charge. What equipment would i need? Is a slow charge possible with lifepo4?

the battery would be using it with would be a 36v 15ah ping battery

"simplest" method is to use the panels in an array that will run an MPPT / inverter to give you the same AC output you'd normally run your charger from, then just plug your charger into that. Not all that efficient, but easy to set up.

There are also some chargers apparently designed to run "directly" from solar (there are some threads discussing that from a few months back, I think, if you search on "solar" and read thru), but I know even less about those than about doing it the other way.

36v solar charge controllers used to be a bit hard to find, but maybe not anymore. The other way, would be a 12v charge controller, 12v storage battery, then an inverter, then your charger. Losses at each step, but you at least get to store 100% of what is coming out of the charge controller since the storage battery is always there to recieve it. It sounds inefficient, but might be more efficient than having your panel in the sun charging nothing if you are out riding.

And it's there to run a small appliance if the power shuts off. Watching the weather channel this week, Sure glad I have some generators. Imagine being in Virginia in a heat wave, and no power for a week! No ac, all your stored food in the freezer gone, etc.

Central Ohio still has a good amount of people without power today. I know my parents are without power atm as well.

So yea this type of thing sure gets the brain thinking about backup power.. At least I have a crazy amount of life and lipo I could use
to run fans and things , but not really a fridge.

Bought the generators to use when camping at the lake, then ended up using them a LOT more to power the house. We call it the regularly scheduled blackout in summer. One bolt of lightning as close as ten miles does it. The "grid" at my house is more like a long dead end road, and often shuts off for about 2 hours.

I get my AC running again whithin 15 min. Have plugs in the house that connect only to the generator, though a plug on the outside wall.

It's useful to have a battery bay. This allows you to charge batteries at night, and gives you electricity during a power outage. Avoid those rediculous 300v, power grid assist panels that people seem to get suckered into. If you have a power outage and you have one of those goofy "assist" pannels on your house you will still end up with no power in an outage. Like amberwolf said, you can just use an ac inverter, they are about $200, and come in handy because they allow you to run ac stuff off your dc battery bay. A DC DC converter would be cheaper and more efficient though. You can buy one for about $30, reduce to 36v, and connect a 36v dc lifepo charger.

parajared said:

Avoid those rediculous 300v, power grid assist panels that people seem to get suckered into. If you have a power outage and you have one of those goofy "assist" pannels on your house you will still end up with no power in an outage.

Click to expand...

You know, if you have one of those, you can also have a battery bank and inverter to use during emergencies, and just keep it charged off the plug. But you'll also be getting credits to your utility bill to help pay for that stuff.

Chalo

I think hipower ebikes has a solar blanket that charges at 48v for about 700-900usd. On a 36v solar panal does it go high enough to charge a 36v ping at what 40v ? AW has the easy way, but the cost and the lost of charge energy.

999zip999 said:

I think hipower ebikes has a solar blanket that charges at 48v for about 700-900usd. On a 36v solar panal does it go high enough to charge a 36v ping at what 40v ? AW has the easy way, but the cost and the lost of charge energy.

Click to expand...

Kind of expensive at ~$2500. I've also been thinking about this for camping trips or something..

I think thw solar blanket from Hi-power bikes or something was 700usd and is over priced. I don't know if a 36v solar is at a high enough to charge a 36v lifepo pack. What your end voltage 41v. ?

I'm not sure if you were thinking of somewhere else?

http://www.hi-powercycles.com/product.sc?productId=101&categoryId=7

Hope that is 2,000 pecos It only 120 watt so 8hr plus charge time on 48v. good for riding at night and charge all day ? What

http://www.otherpower.com/ is a site for living off-grid, also http://www.builditsolar.com/. A lot of cabins and sailboats start out with a small system using 12V, simply because there are so many off-the-shelf (OTS) components, especially if you look at 18-wheeler and RV supply sites.

The next bump up is a 24V system, there are charge controllers, inverters, and solar panels that are ready to go at 24V.

The most popular systems for serious off-gridders is 48V. Unless you want to do some expensive experimentation, the OTS stuff is 48V. The last few years, lead has gone way up in price, but you could easily put together a solar charging station with 48V of the very large deep-cycle Trojan flooded-lead-acids (FLA), they can be bought with 6V cells, or 12V, and since they are extra deep-cycle the plates are about as thick as your thumb...

-while mppt controllers give you additional charge current using a buck switcher, you don't 'have' to use a controller at all if you're willing to watch the battery charge. you then become the 'controller'.
(whatta you do for a living son?- "oh, I'm a controller")
All you need is about 3-12V panels hooked in series or enough solar cells in series for an open-circuit voltage of around 50-55V.
Hook the connection up to your 36V battery and wait until done. (whatever chemistry you've got).
You might wanna undercharge a tad.
If you're an analog electronics kinda guy use a voltage comparator circuit to shunt the panels' output from the battery when the voltage reaches your desired goal.
You can also use small arrays of solar cells to charge your battery pack's individual battery cells, with several 'one chip' charge controller solutions available from various linear electronics chip manufacturers. These chips sometimes include a built-in mppt and most (but not all) are isolated meaning you can stack'em for more voltage and/or current.

"Oh I'm a controller" Yea and your out the door Victoria. That was a great day. That was a good move. Thanks ddk i remenber that.

I haven't done this but also intend to do a solar system,
this is what I'd do:
1. buy solar cells and do the tabbing/diode/connections myself ( lots of cheap ebay sellers)
I would use monocrystalline 17% efficiency ( some a bit higher prices are ok these days)
Or buy pretabbed alot easier. For a slow charge maybe $120usd for the cells, faster charge maybe $200usd plus for cells.
2. buy an mppt off ebay ( 10amp enough) ( $30-$50usd)
3. buy a decent size sla lead battery ( or whatever I happen to have handy) buy locally
4. charge up the lead battery via mppt ( car battery would do) and use an rc charger eg. turningy are good and not too expensive from hobby king
Just charge off the lead acid battery whenever you have too, leave it charging all the time ( mppt should cut off when its full)
turnigy chargers about $50usd problem will be you will need two chargers ( can only go to 24v on each charger), but they will run efficiently directly off
12v car battery.

ddk said:

-
All you need is about 3-12V panels hooked in series or enough solar cells in series for an open-circuit voltage of around 50-55V.
Hook the connection up to your 36V battery and wait until done. (whatever chemistry you've got).
You might wanna undercharge a tad.
If you're an analog electronics kinda guy use a voltage comparator circuit to shunt the panels' output from the battery when the voltage reaches your desired goal.

Click to expand...

DANGER Do not direct connect a Solar panel to a LI PO battery. If the battery is charge above 4.25 V per cell then CA-BOOM oh damn there goes another dreamliner!!! So a36 V Lipo with ten cells should not be charged above 42.5 V.

On the other hand connecting a lifepo4 should be safe because that kind of battery can handle a lot higher voltage than its nominal voltage. Could a battery guru please confirm this?
in other words the open circuit voltage of the solar panel must be less than the highest battery voltage allowable.

Charging batteries directly from solar panels is tricky because of the mismatch between pack voltage and panel voltage. To further complicate matters, you will only get peak power from your solar panels by carefully managed their output voltage and current (called 'finding the knee of the I-V curve'). More about getting the most from solar panels here:

http://en.wikipedia.org/wiki/Maximum_power_point_tracking#I-V_curve

Normal practice is to use a maximum power point (MPP) tracker device between the solar panel(s) and the battery bank, but that practice works best for relatively safe SLA deep cycle batteries. Most solar panels are engineered to work with SLA voltages. Even then, using a MPP tracker still does not provide proper 'end-of-charge' voltage limit and current tapering required by LiFePO4 batts.

However, there may be an better alternative to a MPP tracker that could work with LiFePO4 batteries... (YMMV)

It might be worth it to try using the solar cells paralleled together to provide a 12-18v input to a RC LiPo charger. Make sure you use a charger that can accept a range of inputs between 12-24v, there are lots of models that do so. Then setup the RC charger so that it limits amp (current or 'I') draw to 1 amp for every ~18 watts of rated power from your solar array.

The RC charger will correctly provide the finishing voltage and current tapering your LiFePO4 batts need, all while producing very close to max power from your solar panels.

In fact, the RC charger's input power current limiting feature may give you free bonus MPP tracking capability. 8) After you've estimated the appropriate current limit for your solar array in amps and begun charging, try changing the input current limit. First +1 amp, then -1 amp. Watch how much power is produced by the RC charger as the input current changes. You should be able to quickly find the input amps setting that maximizes the power output of the charger. This number will vary with sunlight (of course), panel placement (perpendicular to the sun in best), and the outside temperature (cold panels make more voltage). Experiment, and experience will be your teacher.

In effect, you will become your own MPP tracker. Congratulations, you've replaced a machine! Take that, Drone Army!

Cheers, and enjoy that sunshine!
Holocene

whatever said:

I haven't done this but also intend to do a solar system,
this is what I'd do...

Click to expand...

Yup, that works well. I've been doing it since I created my system in May 2000.
Nice part is the solar energy is captured during the day while I'm out, and then I use it to charge my ebike when I get home after the sun goes down 8)

Cheers, and have fun!
Holocene.

All this sounds so complicated, says a man with two 12v panels a 100ah battery storage sla and a cellpro powerlab 1300w rc lipo charger. But Why cant you just connect one or two panels in series rated at 20% more voltage than you need (to account for possible shading) and hook it right into the bms charge port.

I know mr ping hasnt got perfect english but im sure when I asked him the same question he told me this was fine as the bms will shut down once a cell goes too high just like it would with the ac charger. The pack will drag the pv voltage down to its own needs but i guess waste a little over mppt tech. At least your not using pwm pulses into a battery that doesnt need that sort of treatment.

On occasion I take an overlander pro rc charger with me on a ride (its only tiny) and 4x10ah headway cells. I set it to 17 pb lead acid cell count and it terminates at around 41.5 (3.45v a cell) volts on my 12s lifepo4 pack. I manually monitor the voltage. The charger shuts down when the headways hit 11.5v having boosted me by a whole 3ah max.

Solar House installations often run double the household voltage so even when the sun is weak it will pump out something useful that doesnt need boosting. If we ever get any sun soon I might try it with my 40w panel. It is nice to know I have 100ah of lead charged and some panels just incase.

Ps I once tried a 500w inverter (12v-240v) to charge a drill pack and camera battery with the standard ac chargers. it damaged both batteries. This may have been due to it being a modified sine wave inverter. It may have been odd luck but get a pure sine wave inverter for this sort of stuff if you can.

for an mppt and voltage cut off in one, you can use solar race car mppts, there must alot of old ones sitting around in boxes at universities etc
New ones are expensive but available.

sapo said:

ddk said:

-
All you need is about 3-12V panels hooked in series or enough solar cells in series for an open-circuit voltage of around 50-55V.
Hook the connection up to your 36V battery and wait until done. (whatever chemistry you've got).
You might wanna undercharge a tad.
If you're an analog electronics kinda guy use a voltage comparator circuit to shunt the panels' output from the battery when the voltage reaches your desired goal.

Click to expand...

DANGER Do not direct connect a Solar panel to a LI PO battery. If the battery is charge above 4.25 V per cell then CA-BOOM oh damn there goes another dreamliner!!!

Click to expand...

apparently you don't understand how charging batteries works.

YOU are the BMS i.e you watch a voltmeter hooked across the battery terminals. Hook the panels with a 50-55V OPEN CIRCUIT voltage reading to tha battery. The Volt meter now reads the current battery voltage.
Watch as the meter s l o w l y changes-
...until it climbs to the termination voltage of your choice whereupon you disconnect the panel(s) from the battery.

If you do NOT know how to deal with LiCo batteries, you Must learn that first.
I do.
I use solar panels both direct charging 10s batteries and with mppt chargers charging 12V batteries whose outputs feed rc chargers
everyday
every day

Your uninformed fears are what makes this world what it is.

I have had very good luck solar charging lifepo4 directly using a spare Outback MX-60 charge controller. You can run a variety of pack voltages, and incoming panel voltages. This controller (and others out there), allows for you to set the output voltage, amps, and a few other things if you're a bit crafty.
http://diesel-bike.com/Aurora/aurora_files/Velomobile_MX_60_Charge_Station.jpg
~CrazyJerry

it does make sense to be using a regular balancing charger instead of having to go through an inverter to bulk charge. from the design i have seen in the icharger it looks very efficient and you won't be losing energy in the conversion through the inverter back to the bulk charger and balancing resistors.

from looking at them, it looks like the balancing charger could even run off of voltage lower than the 12V minimum spec, but lower current. not sure how to hack that but it would require adjusting the input voltage regulation. which may be simple, may be hard.