Solar Powered Trickle-Charger

These are available cheap....

https://www.amazon.com/s/ref=nb_sb_ss_i_6_21?url=search-alias%3Daps&field-keywords=solar+trickle+chargers+for+12+volt+batteries&sprefix=solar+trickle+charger%2Caps%2C161&crid=3GP3H5PQ846K1

I have a few myself....when my vehicle is going to be parked for an extended time + 1 month...I unhook the battery and place the solar pv panel on the dashboard, then hook to battery via charge controller...

Since you are in business class, I suspect you have two separate problems to solve. The first is the technical part: How large a solar panel do you need, how much charge current can you get from sunshine and how much do you need to keep the batteries charged. The second problem is whether there is a market out there for this product and can you build it for a competitive price.

Critically, we need to know what is running off these batteries, and what that current is. Are you trying to design a solar-powered semi-truck (basically impossible by current standards)? Or is this to prevent battery self-discharge while the truck is stored for long periods?

You can determine the panel wattage once you know how much electricity is drawn (amps) and the voltage (12 V since you are wiring in parallel).

Watt = amp x voltage

A larger panel will give you more wattage. Google different watt size PV panels to get an idea of the dimensions. The panels SolarEagle pointed to are small (1-5 W) and meant to be mounted on dashboards or windshields to reduce self-discharge and sulfide build-up, which further degrades the battery.

You will likely need a charge controller for long-term storage or anyhting higher than a few watts. (Google that to; we don't do homework for you here.) Finally, ensure you have a diode in the PV panels to prevent reveres discharge (Google again. Or maybe Bing to change things up).

I certainly don't understand why someone would mark that post as OT! Here's a GA to counter that!

Quite likely the OT vote was a typo. I've done that before and caught myself in time. And I'm not marking this one OT.

It would be nice if one could retract a vote without changing it to the opposite vote.

This will help when you have dual charging sources...

https://roadslesstraveled.us/charging-rv-marine-batteries-solar-power-shore-power/

To give clarity to all, the product would be a car battery that can do all that a normal battery can. However, it would be connected to the other batteries in the truck and the solar panels giving it energy would provide just enough energy to keep the other batteries from going flat until the trucks next use.

I wondered about that, too, but realized that solar may not be available when the batteries need to be trickle charged, say if the trucks are stored overnight. The solar would charge the solar battery so that there was charge current available anytime the truck batteries were attached.

So the separate battery would have a switched connection to the other batteries, and be held in reserve when no charging was available...?

If I were doing this, for whatever reason, the solar panels would charge the batteries through a charge controller, whenever there was sunlight. There would be connections to connect to other batteries, either on a shelf or through cables out to parked trucks. Charge controller would provide charging current to truck batteries from solar battery, whenever they were connected, providing the whole shooting match didn't "go flat."

Why not just have a jump starter?

Sure! What kind of connector does it have for the solar panels? Does it provide trickle charge so the chemical damage that occurs when the battery charge level goes too low is prevented? Can the students build a COTS solution into their business model?

Well just how long are these truck batteries to be stored?

..."A SLA (Sealed Lead Acid) battery can generally sit on a shelf at room temperature with no charging for up to a year when at full capacity, but is not recommended. Sealed Lead Acid batteries should be charged at least every 6 – 9 months.Oct 18, 2017"...

I would disconnect the batteries during storage and start the trucks every 30 days...You can't let a truck sit indefinitely and expect it to perform properly when needed, it has to be maintained, driven, engine heated up to operating temperature, brakes exercised etc etc...

Like I said, "If I were doing this, for whatever reason..." That's what the "customer wants!" I mean, I could take some guesses at how the conversation went in the class and how they ended up with settling for an idea to solar charge sitting truck batteries.

You can start an 18 wheeler with 3 batteries, but if the semi sits for 2 days or more it may not start, that is why they require 4 batteries, that forth battery will help start the engine even after a week of sitting, the reason for this, is because the ECM is always pulling power from the batteries. With our product, our battery could be put in the 4^th spot, constantly providing the other 3 batteries with energy to keep them from dying out.

OP has done his research!

Point being, he asked for help with the design, not whether or not trucks actually need this product.

OP: Do you intend to make this from the circuit board(s) on up or incorporate off the shelf products into a system package?

It's not the ECM pulling that much power, it's the accessories such as a/c and fridge, tv etc...If I had a truck like this I think I would invest in a small inverter generator...or perhaps even an APU....

https://solutions.letstruck.com/Answers/View/1662/3+batteries+or+4

http://www.hp2000apu.com/apus-vs-portable-generators-for-trucks/

I see that you got a good answer from someone.

As for the 2-3 days sitting and it won't start nonsense, somebody was seriously pulling your leg.

I used to let my truck sit for 2 weeks and when I went to start it, it fired right up no problemo.

In semi-trucks, there are multiple battery's to keep the truck going when one goes out on long trips.

All modern trucks ( big rigs ) have a battery protection circuit that cuts off all power to accessories, leaving only the starting circuit engaged. And as SE pointed out, the batteries (4) will stay charged for 6-9 months.

Auxiliary Power Unit...

Totally awesome....

http://www.hp2000apu.com/products/hp2000-auxiliary-power-unit/

Would it be feasible if we were to change our product to a single battery that replaces the 3-4 batteries in the truck and, because it passively collects energy from the sun, it wouldn't die out during long trips? Should we change it or should we keep the same product?

Very unlikely...

The first thing you have to know is what the total electrical demand is....How many accessories does the truck have? How long do you want to run them without the engine running? The typical truck with sleeper facilities will have many accessories...

Typical Line-haul sleeper truck electrical requirements

Typical battery

..."Power in Watts = Current in Amps x Voltage. A battery rated for 100 amp hours will provide 5 amps for 20 hours. If we have a 12 volt battery, we multiply 100 by 12 and determine that the battery will provide 1200 watt hours."...

http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-fundamentals/amp-hours-vs-kilowatt-hours/

Now what is your solar panel producing in watts? The typical truck in our example requires 2950 watts...

...."As of 2018, a typical solar panel produces around 320 watts of power, but panels come in many different wattage ratings, and finding one that produces exactly 320 watts is rare. The top 10 residential solar panels for 2018 includes panels rated to produce anywhere from 290 watts to 360 watts.Aug 7, 2018"...

You would need a system roughly twice this size to meet that need....

1590 WATT SOLAR WITH 6000 WATT PURE SINE POWER INVERTER CHARGER 120/240VAC 24VDC

$7,999.00 $6,079.28

https://theinverterstore.com/product/1500-watt-solar-6000-watt-pure-sine-power-inverter-charger/?gclid=Cj0KCQiA_s7fBRDrARIsAGEvF8S0FOShlpXOAHxztoRDlaEeUodOuqLs4wtu0oa2Vh3vQYN8QRmtn8IaAklXEALw_wcB

Unfortunately this system would only work in full sun, totally useless at night, so you would need either batteries or an alternative power source to supply base load requirements during the night hours and cloudy days and the hours when the sun was not directly overhead of your solar panels....which would be most of the time....This is why an APU system would be the best choice...

The advantage of supplying your own battery is that it can be electrically separated from the others by an isolator, allowing it to charge on the solar when available and only discharging to the other batteries when needed.

But here's the deal. The engine takes so much current to turn it over with the starter, that it exceeds the current available from a single battery. Therefore, multiple, high-current batteries would be used. As the batteries get older, undesirable chemical reactions increase internal resistance, which lowers the CCA (Cold Cranking Amps).

Further complicating it, many truckers run lots of accessories overnight when they are not driving. This actually requires another type of battery, a deep cycle, with different internal structure, not great for high CCA.

That's why, years ago, if you went to a truck stop at night, they were all parked and running, all night to power accessories, especially if they had a refrigeration unit. This consumed lots of fuel and produced lots of exhaust. Auxiliary Power Units (APUs) can provide this power, using less fuel and producing less pollution but still producing it.

This identifies our design challenges. Aging of high CCA batteries and drain due to accessories.

It sounds like your unit will address both problems, in some ways, but not both at the same time. You (marketing) can't redesign existing trucks or dictate how truckers solve their problems. You can offer products to address both, however. Offer one as a 4th high CCA battery with solar backup reserve (it's isolated so it's kept in reserve despite whatever else they run). This could even be 2 or 3 batteries but then you need a larger solar array to keep it charged. Then, you could also offer one as a solar backed deep cycle, just for their accessories so their starting batteries are preserved.

Your biggest marketing challenge will be the fact that all the batteries are generally recharged when the engine is running, so why the solar? Since solar is available during the day when they are usually driving, do they have to be mounted on top of the trailer? How do you connect them to the cab where the power is actually used. The reserve and back-up will be your biggest marketing angle.

Also, who are you marketing to? Drivers that drive almost every day and have high demands at night or drivers who may have several days of downtime and need to be sure their batteries are ready when needed after sitting for extended periods. SE's post should give you a good idea of power needed in the first case.

Our group is changing our target demographic from trucks to boats. If its in a boat, then could it be feasible to have our battery as the main power source and the solar panels to keep the battery from going flat?

This may be a better market. At sea, or even very far from a the marina in a lake, there are precious few parts stores and AAA doesn't run service!

However, there are probably more tough challenges. Most people will charge their battery overnight, before a trip if it has been more than a week since the boat was last used. Small boats may not want a second battery so you will have to provide a way to protect the solar panel if they have it hooked up when they try to start the motor.

Also, there are going to be some issues with having the solar panel in the presence of water, especially salt water. If it's portable and they only set it up when they are at anchor, there will be other issues. You will have to make it a 14 V panel. I got across 12 VDC while in a wetsuit after a dive and it felt like 120 VAC!

How and where will it be mounted so it faces the sun when they are under weigh or at anchor (boats can swing over 90° in a breeze at anchor!)?

Now we have the idea to change it from a battery that works in the vehicle normally to a battery that only stores energy in reserve from the sun. It would still be giving the other batteries energy to keep them from going flat, but it would also be able to jumpstart the other batteries if need be. Is that a smarter change of product or should we keep it as the battery that does the same as any battery.

You can't "jump start" a battery. You can jump start an engine.

It takes a lot of power (Voltage * Current) to start an engine. A weak battery commonly has a fair percentage of its normal voltage under no-load conditions, but its internal resistance "uses up" a lot of that voltage under heavy load. A 12V Lead Acid battery whose no-load voltage has dropped to 10V will drop to something like 5V or even lower when connected to the starter motor.

During the jump start process, the added battery supplies the power to run the starter motor and get the engine running. It does NOT add significant energy to the weak battery, because it is not connected for a sufficiently long time. The vehicle's generator/alternator must recharge the weak battery over a significant time (many minutes to an hour or more, depending on how low the original charge was).

In order to use the solar-charged battery for jump-starting, which is not a bad idea, you must provide a separate very heavy relay, similar to the normal starting relay (capable of carrying several hundred Amperes), to connect the solar-charged battery to the starter motor only during the jump-start. The alternative would be to use a manual connection similar to normal jumper cables, except that only the hot wire would be required, if the ground was a permanent connection.