charging a 24V trolling motor setup

hharke

I have a 24V trolling motor run by two 12V excide 27MDC batteries (Amp hr-100. MCA-730 and RC-160).  They are hooked in series to get the 24V.

We are putting the boat in a dry slip and need to use a solar charging system for the two batteries.   I do not think they will be down over 50% when done fishing and used every 3 days at most.  We are talking around salt water too in NC.

No permanent install.   Plug and unplug and remove panel while fishing.

Do I use one 24V panel and what size?   

Or do I use separate 12v panels to each battery?

Figured out I need the MPPT controller but will a 10 watt work?

Really do not want the huge 200 watt panel that is 3 ft by 5 ft, just to unwieldy.  

thanks

BB.

Welcome to the forum hharke.

Frist some basic math: if you have 2x 100 AH @ 12 volt batteries discharged to 50% maximum:

• 100 AH * 24 volts * 0.50 discharge = 1,200 Watt*Hours per day

To recharge the battery bank--Fixed solar array in:

Wilmington
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 56° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.55	3.98	4.91	5.45	5.34	5.17
Jul	Aug	Sep	Oct	Nov	Dec
5.10	4.80	4.69	4.74	4.05	3.60

Now, you can recharge fully in one day, 2, days, 3 days... Assume ~4 hours per day minimum sun in good fishing weather:

• 1,200 WH per day * 1/0.61 DC off grid solar eff * 1/4 hours of sun * 1/1 day of recharge = 492 Watt array 1 day recharge
  
• 1,200 WH per day * 1/0.61 DC off grid solar eff * 1/4 hours of sun * 1/2 day of recharge = 246 Watt array 2 day recharge
  
• 1,200 WH per day * 1/0.61 DC off grid solar eff * 1/4 hours of sun * 1/3 day of recharge = 164 Watt array 3 day recharge
  

And then there is the 5% to 13% rate of charge... You can get away with 5% recharge for weekend/seasonal usage. 10%+ rate of recharge for lead acid batteries is recommended for daily/year round usage:

• 100 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 188 Watt array minimum
  
• 100 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 375 Watt array nominal
  
• 100 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 490 Watt array "cost effective" maximum
  

So--You have some guidelines to think about for solar panel sizing.

And some quick comments.

In general, "Marine" batteries are not great deep cycle batteries. They may not last as long in heavy discharging/daily usage. True deep cycle batteries will last longer.

Solar panel/array voltage... You need ~35 to 40 Volt Vmp array rating. Many "24 volt" solar panels have Vmp~30 volts--This is too low of voltage to recharge a lead acid battery bank quickly/efficiently. There are Vmp~36 volt solar panels out there (72 cell)--But you have to hunt round to find the proper brand/model numbers. Otherwise, using a pair of Vmp~17.5-28.6 volt panels (i.e., "12 volt 36 cell panels") in series would be the better choice.

Note--There are PWM solar charge controllers (cheaper--good enough for many smaller installation) that need to "exactly match" panel voltage to battery bank (i.e., Vmp-array ~ 35-40 Volts Vmp). And there are MPPT type solar charge controllers--Much more expensive, but you can have Vmp array ~ 35 to near 100 VDC. You can put two (for example) Vmp~30 volt panels in series for Vmp-array ~ 60 volts and properly recharge the battery bank.

Note that many solar charge controllers can be "confused" (or even possibly damage your controller or battery bank) if you simply connect/disconnect the battery bank. You should always turn off the solar array first before disconnecting the battery bank from the solar charge controller (or put the charge controller on the boat connected to the battery bank--And put the disconnect to the solar array).

Does the above help? Any questions?

-Bill

hharke

Any questions? ha tons of them.

1.  I planned on mounting the MPPT controller permanently on the boat and just hooking the panels to it.  Is that a correct way to do it?

2.  What controller do you recommend?

3.  I will change out the batteries to true deep cycle when the go, so must figure that in also.

4.  Based on your calculations, if I want to plan on a 2 day recharge I need 246 watt of solar panels?  Correct?
      It will actually be routinely 3 or more days, but want to plan for 2 day recharge.  

5.  Panels must have total of 35-40 volts array, and can achieve that with one very large panel or two smaller panels (30 Volt) in series. 
     Is that correct?

6.  OK, what two smaller panels do you recommend?

Note, no permanent installation except the controller on the boat for hopefully simple plug in and leave it to charge.  Boat will be lifted out of the water and put in dry slip that is stacked 4 high and pretty much open to sun all the way around.  Panels will be either on deck or hanging on frame of T top.and remove when leaving.

BB.

hharke said:

Any questions? ha tons of them.

1.  I planned on mounting the MPPT controller permanently on the boat and just hooking the panels to it.  Is that a correct way to do it?
Yes--That will be fine (keep controller dry/free of salt spray/etc.). Controllers (especially MPPT) do have waste heat--So some ventilation will be needed.
2.  What controller do you recommend?
If you stay under ~565 Watt solar array (on a 24 volt battery bank), the MorningStar 15 amp MPPT controller (get the Remote Battery Temperature Sensor is probably the best bang for the buck.
MorningStar & Midnite Solar make some larger (and more expensive) controllers that work well too. Outback is also a long time good brand, see new units there (I am not in the solar biz--And I do not work for our host--Look at the units and see which ones may be of interest to you, and ask more questions here for others to help you).
Rouge also made a nice unit (updated version I see, don't know anything about it).
Of course, there are a lot of of import units--Some may work fine, others do not.
3.  I will change out the batteries to true deep cycle when the go, so must figure that in also.
6 volt golf cart batteries are nice (cheap, rugged). However, 4x 6 volt batteries will give you around 200 AH @ 24 volts--May be a bigger bank than you want (size, weight). Also, you should have a larger solar array (see how things "grow" as you look ahead?).
4.  Based on your calculations, if I want to plan on a 2 day recharge I need 246 watt of solar panels?  Correct?
      It will actually be routinely 3 or more days, but want to plan for 2 day recharge.  
Guessing your typical 50% discharge plan, and boating for ~9 months of the year, yes. Of course, solar electric only works in clear weather--If you have coastal fog/clouds and/or a week of cloudy weather, your harvest can be 1/2 to 5% of "name plate" for that day/time period. Solar does not collect much power on dark days.
5.  Panels must have total of 35-40 volts array, and can achieve that with one very large panel or two smaller panels (30 Volt) in series. 
     Is that correct?
For PWM charge controllers, 35-40 volts is the optimum range. For MPPT controllers, ~36 volts is minimum, and (typically) maximum voltage is ~100 VDC (cold solar panels run higher voltage than hot panels). You have to check each controller--For example the MorningStar 15 amp controller has Vmax of ~75 input--and 2x Vmp~30 volt panels in series (Vmp-array~60 volts) is probably too high of voltage (controller max input is rated Voc-cold--voltage open circuit cold).
6.  OK, what two smaller panels do you recommend?
This gets complicated--First, I am not in the business--I can point you to our host (they have very good customer service)--But they may not be the best for you (solar panels can be very expensive to ship--You want to make sure you have the total price to your front door).
Also, solar panels under ~140 Watts can ship UPS, Bus, and other options. >~175 Watt panels, generally ship by truck (and more expensive to pack and ship a few panels at a time).
Generally, you need to do several paper designs. Look at smaller (140 Watt or so) "expensive" "12 volt panels" and a "cheap" PWM controller vs "cheaper" Vmp~30 volt panels and more expensive MPPT charge controllers. Note, "high voltage" Vmp-arrays are nice if the distance from the array to the MPPT solar charger is relatively long (over ~20 feet or so). If your array is "on top" of your boat slip--Then the size of the copper cable and a Vmp~35 volt array will not be bad.

http://www.solar-electric.com/topoint-jtm-190-72m-solar-module.html (Vmp~36.5 volt panel--two in parallel would be nice)
http://www.solar-electric.com/kyocera-kd140sx-ufbs-140-watt-polycrystalline-solar-panel.html (Vmp~18 volts--two in series)

Note the first panel is ~$1 per Watt (higher voltage Vmp). The second panel (very good mfg, good waranty service, etc.) is around ~$2 per Watt... Common pricing dilemma. "GT Panels" are much cheaper $$$/Watt vs "Battery" rated smaller panels.

http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/hiposopa.html

Don't forget shipping costs.

Note, no permanent installation except the controller on the boat for hopefully simple plug in and leave it to charge.  Boat will be lifted out of the water and put in dry slip that is stacked 4 high and pretty much open to sun all the way around.  Panels will be either on deck or hanging on frame of T top.and remove when leaving.

Remember that solar panels are "single weight" tempered glass. Pretty tough until something scratches the panel (or hard hit, twist panel, etc.)--Then the turn into expensive artwork/coffee tables (shattered panels will not work long in weather).

~175 Watt panels are about the limit that is "easily" moved around by one person.

Suggest array is "permanently mounted"--Moving panels every few days is a high risk of eventual damage. If must move around, then smaller (140 watt or smaller) panels is a better bet.

-Bill

Johann

Partial shaded panels will not put out power, the whole panel need to be exposed to the sun to make power.

vtmaps

hharke said:

  I planned on mounting the MPPT controller permanently on the boat and just hooking the panels to it.  Is that a correct way to do it?

Most controllers must be turned on (by connecting the battery) BEFORE the solar panels are connected.  To shut down, you must disconnect the panels BEFORE disconnecting the battery. 

Therefore you shouldn't just hook up the panels to the controller... you should have a circuit breaker to use as a switch.  I suppose that if you have the panels connected though a DC rated plug and socket, you could just unplug the panels.

The other side of the controller (connection to battery) MUST have a DC rated circuit breaker.

--vtMaps