Solar with no charge controller

heynow999

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Nov 11, 2017
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I have a 14S18P battery pack that I am using to power an outboard motor. I have a thread about it here

https://secondlifestorage.com/t-ideas-for-a-portable-battery-pack-and-inverter

What I want to do is add a Bimini top to the boat, and put solar on that to charge while we are fishing.

I bought 3 ofthese flexible solar panels. They should put out 18v x 3 = 54v so it wouldn't overcharge a 14S pack, which would be 56V fully charged. The idea is to just top up the battery while we are out on the lake. The panels would be dissconnected at the end of the day so it would not be left charging unsupervised.

I imagine the use would go like this. Head out in the morning with a fully charged battery (56V). As soon as it falls to 54v the solar starts charging and will keep it floating aroud 54v. End of the day we would still have an almost fully charged battery to go back with.

https://www.ebay.ca/itm/Mono-20V-10...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

I know solar better than I know lithium batteries. I know that these panels will only put out 100 watts under ideal conditions,but the voltage will stay at around 54v, and the amps will rise and fall.

Will this harm the batteries?

The reason I dont want to use a charge controller are many.
I will only use the boat a days a year so I want to keep things simple.
Setting up the boat is a pain so I dont want to add more complexity.
If I order more equipment my wife will make me sleep on the couch if im lucky.
 
I would recommend a Charge controller Just keeps things in check. Also a BMS to make sure the cells do not go too high
 
You should not connect LiIons directly to the solar panels. They should go through the charge controller. For what you are doing, you could use PWM charger as it's not crucial to pull as much power from the panels as possible. But, if you were going to stay out and run lights or several other battery operated devices, then you would want to. At that, I'd say the MPPT which is mentioned above.
However, if the price difference is only a few dollars, then go with the MPPT over the PWM.
 
OK, I like the one suggested above. Has anyone tried it? Either way i'll order it and give it a test.

I do have a BMS on the battery

One thing I was wondering, how much more range would I get with the solar? Is it worth the effort? (he asks after already buying the panels!)

Could someone help with the math?

I have a 14s18p battery with used cordless drill batteries, but they are all the same model of battery. They are 2000mah. I think I have about 30 ah of capacity, being conservative and allowing for the batteries being used and the inefficiencies of the pack. I believe I could go about 12 miles on a fully charged battery

So heres where I get a little fuzzy but lets give it a try. 30ah/12miles = 2.5 ah/mile x 50v= 125wh/mile

I am going to assume a 4 hour fishing trip, or a least a trip that gives me 4 hours of direct sun. I have 300 watts of solar @ 18v.

I get a little confused at this point, if anyone could finish this that would be great
 
That's a really low draw for an electric motor in a boat. Is that a trolling motor? If you had direct sun and 300 Watts of Soltar you could run without batteries. As a 300W solar array "should" output 300Watts constantly so your 125W draw is less than it's usage.

but but again this seems low for a motor that pushes a boat


Now WattHours are just a measure of the output for 1 hour so for example if your panel outputs 300W and the sun is perfect you will get 300wh but say for some of the time there is a cloud you may only get 250wh for any 1 hour period
 
Also that mpt-7210a is a boost controller only. the panel voltage needs to be much lower than the battery voltage to make it useful. I'd go with a cheap chinesium PPT
 
Look up sod's law. You only need to leave it connected once to damage or destroy your cells - the pack will charge close to the open circuit voltage of the panels, not just the 18V mp.. I have muche experience with sod's law.
 
"but again this seems low for a motor that pushes a boat"
This is the motor. It is i guess the next step up from a trolling motor. It is supposed to be 3hp. I have it on a 9 foot Zodiac and I couldn't get it to plane. It was close, I think maybe my 12 year old son could get it to plane.
http://www.solarnavigator.net/outboard_motors.htm

As we were putting around I realized that if this is not going to plane there is no sense in making a big wake and wasting all that energy. We cruised at around 1/2 throttle. We have only had it out for a few days at this point. 12 miles may be a stretch. I know we went about 8 before it died, but I hadn't fully charged the battery, and the BMS cut off at 46.5v for some reason.
 
1 Horsepower = 745.7 Watts
So 3x that is = 2237.1W
At 12V that's 2237.1W / 12V = 186.425A

That's a lot of amps to be pulling. Now, I would recon that means 3HP at full throttle which you wouldn't be doing on a continuous basis, I would assume.
If you run 1/3 throttle, we can possibly assume that you'd use 1HP, or 745.7W
745.7W / 12V = 62A
 
Korishan said:
1 Horsepower = 745.7 Watts
So 3x that is = 2237.1W
At 12V that's 2237.1W / 12V = 186.425A

That's a lot of amps to be pulling. Now, I would recon that means 3HP at full throttle which you wouldn't be doing on a continuous basis, I would assume.
If you run 1/3 throttle, we can possibly assume that you'd use 1HP, or 745.7W
745.7W / 12V = 62A

The motor is 48v, set up for lead acid of course. Im running it at 14S or ~52v
 
Ahh, that would make sense :p The link above doesn't show what the voltage is; and the "Specifications" link is broken on their page.

Sooooo

2237.1W / 48V = 46.6A
745.7W / 48V = 15.5A

Looks a lot better ;)
 
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