Charging with portable solar power station

[Tfisher309]

I would like to build a portable solar powered charging station for my bike which has a 74v 50ah battery. The wagon I will use will mount a 200w 12v solar panel, a 30a controller, a 12v 100a lifepo4 battery and a 1000w invertor along with my 84v 4a charger.

Am I correct thinking this setup will be able to transfer about 1,000w of power to my bike?

This would not fill my bike battery, but would be more than enough for my short commute.

 

[amberwolf]

I would like to build a portable solar powered charging station for my bike which has a 74v 50ah battery. The wagon I will use will mount a 200w 12v solar panel, a 30a controller, a 12v 100a lifepo4 battery and a 1000w invertor along with my 84v 4a charger.

Am I correct thinking this setup will be able to transfer about 1,000w of power to my bike?

Some thoughts:

There are some good solar-charging setup threads on the forum with actual data on solar output, etc., if you look around. They have better numbers than my guesstimates below.

I'll assume that you meant 12v 100Ah, not 12v 100A for the battery. A is current, Ah is capacity; completely different things, so you really should specify both at the same time. If you can post the actual specs for voltage, current, and capacity it would be useful.

With a 200w source panel, then if it were to be at max insolation and actually outputting it's max rated power, you only get 200w from it. Then the MPPT (or whatever converter you use) has an efficiency loss, depending on design and conditions. Let's call it 20% (you can test how much loss you really get). So let's say you get 160w out of the conversion. The battery itself has some efficiency loss, too, but it's probably small enough to leave out of the equation for guesstimate purposes.

Assuming the battery is 12v x 100Ah, that's 1200Wh. Assuming you got 160W continouously for say, 8 hours, you'd get enough to fill up the battery from empty.

Realistically you probably won't get anywhere near the panel's rated power, unless you have a sun tracker on it, keep it perfectly clean, and are on the equator at high noon. My guess is you will probably see less than half the panel's rated power most of the time, so I'd guesstimate you will probably see 80-100w out of the conversion process, so it will really probably take more like 12-16 hours of good direct sunlight to fill up the battery from empty. Most likely that will average out to two to four days of just letting it sit there and recharge.



Next, for the conversion out of the solar battery and into your traction battery.

Your charger is only about 336W, at max load during the constant-current part of the charging curve. (84v x 4a). So the absolute max charging power you will ever see is that. As the battery fills up, power will drop.

For the inverter, assuming the 1000w is a continuous rating and not peak, it could handle almost three of those chargers, if your battery could handle 12A charging. (depends on the BMS charge port electronics, and the cells themselves, as well as the charger port wiring). Or you could get a bigger charger.

Either way, with 1200wh in the solar battery, it can, at most, recharge a 1200wh traction battery. For an 72v battery (84v full, for a 20s LiIon), that means 1200wh / 72v = 16.7Ah, at most.

If you are using this solar setup on this bike

Newbee with some basic electrical questions

I have a 50ah battery that can supply 150a continuous and 300a peak and a controller that can handle 120a continuous and 200a peak. Here are a few things that I don't understand: The cables from my battery to controller are 8ga. Shouldn't they be as big as the wires from my motor? I have a...

endless-sphere.com

then you have a 50Ah battery, so this solar setup will at best charge that up about 33% from empty.

A 50Ah battery at 72v, will be about 3600wh. If you need the ability to recharge that from empty, you'll need a bigger solar battery, and a lot more time between solar recharges with that small a panel setup. Or a bigger panel to lower recharging times.


If the usage of the solar setup is intended to be something other than the above, I'd recommend posting what you want it to do, so we can help you figure out how to do that specific job, under the specific conditions you need it to do that job.

 

[Tfisher309]

Some thoughts:

There are some good solar-charging setup threads on the forum with actual data on solar output, etc., if you look around. They have better numbers than my guesstimates below.

I'll assume that you meant 12v 100Ah, not 12v 100A for the battery. A is current, Ah is capacity; completely different things, so you really should specify both at the same time. If you can post the actual specs for voltage, current, and capacity it would be useful.

With a 200w source panel, then if it were to be at max insolation and actually outputting it's max rated power, you only get 200w from it. Then the MPPT (or whatever converter you use) has an efficiency loss, depending on design and conditions. Let's call it 20% (you can test how much loss you really get). So let's say you get 160w out of the conversion. The battery itself has some efficiency loss, too, but it's probably small enough to leave out of the equation for guesstimate purposes.

Assuming the battery is 12v x 100Ah, that's 1200Wh. Assuming you got 160W continouously for say, 8 hours, you'd get enough to fill up the battery from empty.

Realistically you probably won't get anywhere near the panel's rated power, unless you have a sun tracker on it, keep it perfectly clean, and are on the equator at high noon. My guess is you will probably see less than half the panel's rated power most of the time, so I'd guesstimate you will probably see 80-100w out of the conversion process, so it will really probably take more like 12-16 hours of good direct sunlight to fill up the battery from empty. Most likely that will average out to two to four days of just letting it sit there and recharge.



Next, for the conversion out of the solar battery and into your traction battery.

Your charger is only about 336W, at max load during the constant-current part of the charging curve. (84v x 4a). So the absolute max charging power you will ever see is that. As the battery fills up, power will drop.

For the inverter, assuming the 1000w is a continuous rating and not peak, it could handle almost three of those chargers, if your battery could handle 12A charging. (depends on the BMS charge port electronics, and the cells themselves, as well as the charger port wiring). Or you could get a bigger charger.

Either way, with 1200wh in the solar battery, it can, at most, recharge a 1200wh traction battery. For an 72v battery (84v full, for a 20s LiIon), that means 1200wh / 72v = 16.7Ah, at most.

If you are using this solar setup on this bike

Newbee with some basic electrical questions

I have a 50ah battery that can supply 150a continuous and 300a peak and a controller that can handle 120a continuous and 200a peak. Here are a few things that I don't understand: The cables from my battery to controller are 8ga. Shouldn't they be as big as the wires from my motor? I have a...

endless-sphere.com

then you have a 50Ah battery, so this solar setup will at best charge that up about 33% from empty.

A 50Ah battery at 72v, will be about 3600wh. If you need the ability to recharge that from empty, you'll need a bigger solar battery, and a lot more time between solar recharges with that small a panel setup. Or a bigger panel to lower recharging times.


If the usage of the solar setup is intended to be something other than the above, I'd recommend posting what you want it to do, so we can help you figure out how to do that specific job, under the specific conditions you need it to do that job.

Good information, thank you.

If I can gain 1000w every two to three days I am good. I know my proposed system is weak, but it only needs to cover, at most, 40 miles of city driving a week.

Other applications for the battery and inverter could be electric lawnmower, boondocking with small travel trailer, or assisting my 2000w generator with essential services during a power outage.

If needed, there is room on the wagon I'm using to add another 200w panel.

Financially this project doesn't make sense. The electricity where I live is cheap and reliable, but the thought of riding a motorcycle without burning anything is very appealing.

Thanks again, Tom

 

[amberwolf]

If I can gain 1000w every two to three days I am good.

Remember Watts W and Watt hours Wh are completely different, and it is very important to use the right unit.

For instance, you cannot gain 1000W, at all, with this method. But you *can* gain some Wh. (how many, depends on the insolation and your panel/etc efficiency)

I know my proposed system is weak, but it only needs to cover, at most, 40 miles of city driving a week.

Well, to know what it has to cover, you need to know how many wh/mile your driving takes. For the average motorcycle, that's probably roughly around 100Wh/mile, depending on conditions, speed, terrain, weight, stop/start, how hard you accelerate, etc.

If that's the case for yours, you need about 4000Wh (4kWh) of capacity to cover 40 miles. I'm not sureq your system can do that in a week; you'd have to test out what actual power you get out of the panel under your conditions while it's charging the solar battery.

If you have a wattmeter like the Cycle Analyst on your bike, you can measure this directly as Wh/mile. (this is more accurate than the methods below, as it directly calculates this number based on actual power usage at every moment in the ride).

If you have a more basic wattmeter, you can calculate it, by resetting it's Wh counter before a ride, then doing a typical ride under typical conditions, then noting down the Wh counter at the end of the ride, and dividing that by number of miles, for a basic Wh/mile.

If you have no wattmeter, you can guesstimate it by fully charging the battery, taking a ride, then recharging the battery while standing there with a stopwatch, measuring the time to recharge. Since you can guesstimate the charging current at about 4A, then multiply that by how many hours it takes to get the charger light to green (finished) the first time (before it starts the on/off cycling for balancing the pack). That gives you a rough Ah total used. Multiply that by your average pack voltage (72) and that gives you Wh total used, which you can then divide by the number of miles you rode on the trip, to get a rough Wh/mile.


If you have no way of measuring anything, you can use the ebikes.ca motor simulator to "build" a system that performs about like yours under your conditions, and use the estimated Wh/mile it calculates....this will be the least accurate and most complicated method.

Other applications for the battery and inverter could be electric lawnmower, boondocking with small travel trailer, or assisting my 2000w generator with essential services during a power outage.

Just don't try to run your mower directly off the inverter--it's likely the motor's inductive kickback will blow it up either when you turn the mower on or when you stop it. If the mower is battery powered you can use the solar setup to recharge it, though.

The electricity where I live is cheap and reliable, but the thought of riding a motorcycle without burning anything is very appealing.

I agree; I picked up some old small used panels at a thrift store some time back, hoping to come up with a good way to install them on the trike for solar charging (turned out to not be practical since it's parked inside most of the day every day while I'm working); I did test them as a direct-charge (no inverter/charger) for a pack that is "close" to the loaded voltage they put out, but there's no way to regulate that without an MPPT or other conversion device (which I don't presently have), so ATM it can only be used this way while I stand there and watch the voltmeter.

At some point I would like to find a really cheap (probably used) MPPT that puts out say 57-58v at "a few amps" (adjustable), to keep a 2kWh pack charged up that I can then use for whatever. (I have three 14s 2p EIG packs built up that could be charged like that--two are in use, in series, running my B&D wall-AC-powered corded electric mower, which happens to use a regular brushed motor that runs fine on DC, too).

 

[Tfisher309]

Remember Watts W and Watt hours Wh are completely different, and it is very important to use the right unit.

For instance, you cannot gain 1000W, at all, with this method. But you *can* gain some Wh. (how many, depends on the insolation and your panel/etc efficiency)



Well, to know what it has to cover, you need to know how many wh/mile your driving takes. For the average motorcycle, that's probably roughly around 100Wh/mile, depending on conditions, speed, terrain, weight, stop/start, how hard you accelerate, etc.

If that's the case for yours, you need about 4000Wh (4kWh) of capacity to cover 40 miles. I'm not sureq your system can do that in a week; you'd have to test out what actual power you get out of the panel under your conditions while it's charging the solar battery.

If you have a wattmeter like the Cycle Analyst on your bike, you can measure this directly as Wh/mile. (this is more accurate than the methods below, as it directly calculates this number based on actual power usage at every moment in the ride).

If you have a more basic wattmeter, you can calculate it, by resetting it's Wh counter before a ride, then doing a typical ride under typical conditions, then noting down the Wh counter at the end of the ride, and dividing that by number of miles, for a basic Wh/mile.

If you have no wattmeter, you can guesstimate it by fully charging the battery, taking a ride, then recharging the battery while standing there with a stopwatch, measuring the time to recharge. Since you can guesstimate the charging current at about 4A, then multiply that by how many hours it takes to get the charger light to green (finished) the first time (before it starts the on/off cycling for balancing the pack). That gives you a rough Ah total used. Multiply that by your average pack voltage (72) and that gives you Wh total used, which you can then divide by the number of miles you rode on the trip, to get a rough Wh/mile.


If you have no way of measuring anything, you can use the ebikes.ca motor simulator to "build" a system that performs about like yours under your conditions, and use the estimated Wh/mile it calculates....this will be the least accurate and most complicated method.





Just don't try to run your mower directly off the inverter--it's likely the motor's inductive kickback will blow it up either when you turn the mower on or when you stop it. If the mower is battery powered you can use the solar setup to recharge it, though.



I agree; I picked up some old small used panels at a thrift store some time back, hoping to come up with a good way to install them on the trike for solar charging (turned out to not be practical since it's parked inside most of the day every day while I'm working); I did test them as a direct-charge (no inverter/charger) for a pack that is "close" to the loaded voltage they put out, but there's no way to regulate that without an MPPT or other conversion device (which I don't presently have), so ATM it can only be used this way while I stand there and watch the voltmeter.

At some point I would like to find a really cheap (probably used) MPPT that puts out say 57-58v at "a few amps" (adjustable), to keep a 2kWh pack charged up that I can then use for whatever. (I have three 14s 2p EIG packs built up that could be charged like that--two are in use, in series, running my B&D wall-AC-powered corded electric mower, which happens to use a regular brushed motor that runs fine on DC, too).

Thank you for your thoughts. I have some testing to do, but I'm sure the bike is using less than 100wh/mi. The bike weights 240 lb and I am riding in city traffic using regen for much of the braking. I am curious about this and knowing for sure will help me plan my project.

I have a question that goes to the root of my misunderstanding of electricity.

How can a 12v 100ah battery going through an inverter and then a battery charger, charge a 72v 50ah battery?

Let's say the big battery has been drained to 60v. The 12v battery would have about 1200wh and the 72v battery would have about 3000wh.

It seems to me the small battery wouldn't have enough "pressure" ( I'm sure there is a better word) to supply the bigger battery and without diodes in the charger and/or the inverter electricity would actually flow from the larger battery to the smaller.

Maybe I am thinking in terms of water, which I often do when trying to understand electricity.

 

[amberwolf]

Thank you for your thoughts. I have some testing to do, but I'm sure the bike is using less than 100wh/mi. The bike weights 240 lb and I am riding in city traffic using regen for much of the braking.

Regen doesn't get you much back, a few percent at best. If you use a bidirectional wattmeter, like the Cycle Analyst, (or a pair of unidirectional wattmeters, paralleled "backwards", so the input of one is wired to the output of other, and vice-versa, so that one monitors traction current and the other braking current) you can see this directly. Otherwise, you can read up the various posts/threads over the years with actual data on regen, including testing data by Justin_LE.

The only way to be sure of your power consumption is to actually test it via one of the methods I posted.

With high weight, and start-stop traffic (common to city traffic), you end up with higher power usage than continuous riding even at the max speed you reach during start/stop traffic.

Example: My old CrazyBike2 20mph cargobike weighed almost what yours does, plus my own 150lbs+ (at the time...it's gone up since then). In traffic, I'd probably get 30-40wh/mile usage. In continuous riding with few stops (like the canal path, etc), I could get that down to 20-22wh/mile. That includes regen braking from the 2WD 4KW-total DD hubmotor system.

How can a 12v 100ah battery going through an inverter and then a battery charger, charge a 72v 50ah battery?

It can't fully charge it, this is shown in the math I gave in previous posts.

Let's say the big battery has been drained to 60v. The 12v battery would have about 1200wh and the 72v battery would have about 3000wh.

It seems to me the small battery wouldn't have enough "pressure" ( I'm sure there is a better word) to supply the bigger battery and without diodes in the charger and/or the inverter electricity would actually flow from the larger battery to the smaller.

The inverter and charger convert what's in the solar battery to what the traction battery needs. They already have all the parts necessary for this conversion built into them; it is how they are designed and how they work.


If you were to try to directly connect the one to the other, then it would not work, and you would indeed need diodes to keep the higher voltage pack from (over)charging the lower voltage pack, and the lower voltage pack could *never* charge the higher voltage pack *at all* (not because of the diodes, but because it is lower voltage).

 

[Tfisher309]

Thanks amberwolf

So, the current will flow from the solar battery to the battery on the bike even thought there is more wh in the bikes battery. ( In general this is the hard part for me to get my thick head around.)

I understand the need for the inverter and the charger.

 

[amberwolf]

Wh is just the capacity of a battery. How much total energy it contains.

It doesn't matter if the source is 0.001 or 1,000,000 Wh, or if the destination is 1,000,000 or 0.001 Wh, you can "always" convert the Wh from one to feed the other.

If the source is lower Wh than the destination, it can never fully charge the destination.

Also, if the destination is already full, nothing can flow to it. If the source is empty, nothing flows out of it.

If the destination already has 1500Wh of 3000Wh in it, then it will take 1500Wh to fill up; if the source has 1200Wh in it, it will leave the destination only mostly charged, with 300Wh left to fill. (this assumes a perfectly efficient conversion, which doesn't exist...you'd really probably only get <1000Wh into the destination after the inverter/charger losses).

What makes Wh move from one to the other is the inverter, and the charger.


For the purposes of math, it is exactly like charging from a wall socket, except the "battery" that powers the "inverter" that feeds the wall socket is the heat source (coal, gas, nuclear, solar, etc) that drives the gigantic generators the utility company has, and that "battery" is effectively infinite Wh (unless you forget to pay the bill ). Then your charger does the rest.

Does that help?


Side note: Efficiency of conversions grows worse the greater the difference in voltage between the two. So a 12v-120v conversion will be less efficient by some amount than a 48v-120v conversion. Etc.

Meaning, if you can get a 48v solar battery, and 48v MPPT for the panel(s), and 48v-input inverter, then assuming the panels are similar voltage, it would be more efficient a conversion process to get to the charger.

If you could find an 84v-output MPPT, you could directly charge your battery from the panels, for the most efficient conversion of all. To use the panels when your battery is not available for direct connection, then use an 84v solar battery.

Etc.

There's some threads about MPPTs and such, mostly in the Alternative Energy subforum. It's easier to search it using the old forum, which is archived here:
Alternative Energy - ES 1.0 Graveyard
and this is a search for MPPT there, just looking for any instance of it in that subforum:

ES 1.0 Graveyard - Search

The regular search can help you find them by thread instead, if you prefer.

BTW, the very "first" hit in that search links to a post and the one after it with an MPPT that would do the direct pack charging I referred to above:

https://www.amazon.com/MPT-7210A-Controller-street-charging-system/dp/B01DP57PYA

Adjustable 400W Solar Boost MPPT w LED Display

400W Boost MPPT for Solar Charging 24V-85V Battery Output (10S to 20S Lithium).

ebikes.ca

There are also a few DIY Solar forums with more detail than has typically been posted here on ES, like BuildItSolar, etc.

 

[Tfisher309]

Wh is just the capacity of a battery. How much total energy it contains.

It doesn't matter if the source is 0.001 or 1,000,000 Wh, or if the destination is 1,000,000 or 0.001 Wh, you can "always" convert the Wh from one to feed the other.

If the source is lower Wh than the destination, it can never fully charge the destination.

Also, if the destination is already full, nothing can flow to it. If the source is empty, nothing flows out of it.

If the destination already has 1500Wh of 3000Wh in it, then it will take 1500Wh to fill up; if the source has 1200Wh in it, it will leave the destination only mostly charged, with 300Wh left to fill. (this assumes a perfectly efficient conversion, which doesn't exist...you'd really probably only get <1000Wh into the destination after the inverter/charger losses).

What makes Wh move from one to the other is the inverter, and the charger.


For the purposes of math, it is exactly like charging from a wall socket, except the "battery" that powers the "inverter" that feeds the wall socket is the heat source (coal, gas, nuclear, solar, etc) that drives the gigantic generators the utility company has, and that "battery" is effectively infinite Wh (unless you forget to pay the bill ). Then your charger does the rest.

Does that help?


Side note: Efficiency of conversions grows worse the greater the difference in voltage between the two. So a 12v-120v conversion will be less efficient by some amount than a 48v-120v conversion. Etc.

Meaning, if you can get a 48v solar battery, and 48v MPPT for the panel(s), and 48v-input inverter, then assuming the panels are similar voltage, it would be more efficient a conversion process to get to the charger.

If you could find an 84v-output MPPT, you could directly charge your battery from the panels, for the most efficient conversion of all. To use the panels when your battery is not available for direct connection, then use an 84v solar battery.

Etc.

There's some threads about MPPTs and such, mostly in the Alternative Energy subforum. It's easier to search it using the old forum, which is archived here:
Alternative Energy - ES 1.0 Graveyard
and this is a search for MPPT there, just looking for any instance of it in that subforum:

ES 1.0 Graveyard - Search

The regular search can help you find them by thread instead, if you prefer.

BTW, the very "first" hit in that search links to a post and the one after it with an MPPT that would do the direct pack charging I referred to above:

https://www.amazon.com/MPT-7210A-Controller-street-charging-system/dp/B01DP57PYA

Adjustable 400W Solar Boost MPPT w LED Display

400W Boost MPPT for Solar Charging 24V-85V Battery Output (10S to 20S Lithium).

ebikes.ca

There are also a few DIY Solar forums with more detail than has typically been posted here on ES, like BuildItSolar, etc.

Thanks Wolf, you are the man.

You put me out of my misery with the first five paragraphs.

I just went to Harbor Freight and bought a garden wagon to mount the equipment I'll need.

I have only had the bike on the road for two days, but already I like riding it.

I'm calling the bike "Back to the Future."

Thanks again. Tom

 

[amberwolf]

Please note those "garden wagons", like these


don't usually really make good trailers above a few MPH, especially if you have a load in them that is top-heavy, that sticks up above their retaining-wall edge (if they have one) or more than a few inches above the deck (if they don't). They tend to tip over rather than follow you in a turn, and their handle joints and pivot aren't intended to be yanked around at the energies they'll see above walking speed, so they may fail unexpectedly on the road while you're making a turn, etc.


Also, they often don't use actual bearings in their wheels or axles--they may not even have bushings. So wear will be excessive when used beyond the walking speed they were designed for, and it may even be possible for friction to heat the axle and pass-thru / support so much that they weld together.


The one above with just a deck and no sides is probably more stable than the other one, as it's wheels are farther apart in both directions vs it's deck height, but they're both the same quality of construction and designed only to be hand-pulled at walking speed.

You may also run into the problem of legality. On a motor vehicle, your local regulations may require it to be DOT certified and have a registration/license plate of it's own, to be used on any public roads / etc.


A trailer that's made much lower, with the deck/load between the wheels, as close to axle height as possible (or actually below it, like my Mk IV.5 / Mk V trailer here:
Amberwolf's Flatbed Kennel Trailer Mk V ) will be less tippable.

There are a number of possible hitch / towbar designs that can be used with a motorcycle; for CrazyBike2 I copied the automotive ball hitch design that my friend Bill had on his Kawasaki Voyager, which he used to pull a Harbor Fright trailer with a plastic cargo "aero shell" on it for his trips to Sturgis, and so I used a ball hitch receiver on Mk III, IV, and V trailers. But a pintle hitch works, too (I haven't used one, but others have just fine), and there are others.

Whatever hitch is used, I'd still use a chain or steel cable to "tie" the trailer to the hitch so that if it comes off the hitch it A) won't just get loose in traffic, and B) can't have the trailer nosedive into the pavement and dig in, causing the towing vehicle to lose control or crash. I use a short steel cable permanently mounted to the SB Cruiser's hitch, that has a loop engaged by the padlock I put on the trailer hitch lever (to prevent people from trying to steal the trailer when I'm out shopping somewhere).





These types of trailer would be much better suited than the garden cart:

The one bill used was like this one I found in a google image search

Harbor Freight Motorcycle Trailer

 

[Tfisher309]

The green one in the first photo is exactly the one I bought. I don't think I will have any tip-over problems positioning it in my yard for max sun exposure.

 

[amberwolf]

Ah, the way you'd been posting the questions/etc originally, it sounded like you were building a trailer to pull behind the motorcycle, not something to just park in the yard at home.