Sizing a Trickle Charger...and Solar Options

EMKoper · Apr 6, 2016

First, I am an engineer and I am good at multiplying units, but understanding the battery "20 AH Rate" and using that information to size a solar trickle charger (non-regulated) has me a little perplexed. Clarity is desired ....

My 3 battery bank is 2x DC31DT house batteries and 1x DP27 Starter ... I would like to understand the size of a solar unit to trickle charge the full bank. From the Deka website:

*** Note: if you are reading this, the correct approach was not 3%, but 0.3% ... please keep reading! ***

OK ... I have read that a trickle charge is supposed to be 3% of the amp capacity (more that below) .. but I am a little lost in the "20 AH Rate" definition (sorry, engineering confusion, rate is "something"/"something" not "something"*"something" but don't let me overthink this, too) ...

The DP27 "20 AH Rate" is 80 ... I think this means that it have expel 4 amps per hour under a load that totally depletes the battery in a 20 hour period. So this would be an 80 AH battery... right?

The 2x DC31DTs are a rating of 105 ... which means they are each 5 amps per hour under load, so each is about a 100 AH battery ...

So, in total, I have ... (drum roll) .... 280 AH with a full charge by the "20 AH Rate" standard ... this seems basically reasonable but I have never pressed the test first hand on the true working capacity of these batteries.

I have this book, "Sailboat Electronics Simplified" by Casey (page 123) and it says that a maintenance current is 3% of the Amp-Hour Capacity which says I need 8.4 amp for maintenance (280 AH * 3%) or (based on their formula, amps*16V) 134 Watts of solar power to maintain charge under idle conditions. (never mind that the units don't multiple/divide correctly in their equation).

This seems unreasonable ... too high ... too much for simple maintaining a charge ... what am I missing?

EMKoper · Apr 6, 2016

Eureka ...

Ah!! It says 0.3% for maintenance (not 3%) ... let me re-cogitate ... (I guess my eyes are going bad).

0.3% of the Amp-Hour Capacity which says I need 0.84 amps for maintenance (280 AH * 0.3%) or (based on their formula, amps*16V) 13.4 Watts of solar power to maintain charge under idle conditions.

Seems reasonable .... any objections or input?

Thanks for the help ... this, and conversing with myself, was more therapeutic than anything!

So, If I go for a 0.9 amp unit I should be good to go ...

EGregerson · Apr 6, 2016

decimal error

.9 sounds better. that 1st number was high. I have a similar setup; 2 31's and a 27. I have a 54 watt solar panel that generally produces 2.8 amps during the peak hours of the day; i keep the panel covered most of the time. 2.8 is more of a surge than a trickle. But i can check mine on almost a daily basis; so i can cover it or not as needed (the controller should prevent overcharging, but i don't trust it yet). Being in Deltaville, I expect you're a few hours from the boat; so the charger needs to be set up to operate on its own most of the time; is there anything on the boat drawing power while ur away?

EMKoper · Apr 6, 2016

Nothing running on the boat when I'm away--yes I am ~2 hours from the boat!

Did you install recently? (based on your not trusting the controller, yet) Would be interested in how you incorporated it into the electrical system.

markvone · Apr 6, 2016

Eric,

I have a 55w solar panel and ProStar controller, all older and installed by the PO. Battery bank is 3 + 1 flooded group 27s.
I have seen up to 2 amps max, but generally around 1 amp for 4-6 hours each sunny day from the panel.

I only have a bilge pump available as a load on the battery when I am away from the boat. It rarely runs, as I only get water in the bilge from rain running down the mast.

My old battery charger died over the winter (my boat is in the water 12 months) and my batteries and I never noticed until Feb.

I have never had an issue with the solar panel or controller in the five years I've owned the boat. I would recommend a controller for all solar panel installations based on this:

http://www.pbase.com/mainecruising/do_i_need_a_controller

Mark

rbonilla · Apr 6, 2016

hey guys....for a simple set up - On a 1985 Ericson 28..with two 12v marine batteries...is this cheap Amazon - Solar Pannel put out a satisfactory trickle charge to keep juice topped off....??

http://www.amazon.com/ECO-WORTHY-Po...K6PH1S/ref=cm_sw_em_r_sdptod_12qbxb076J9N1_tt

Vagabond39 · Apr 6, 2016

Batteries

EMKooper
The Amp Hour CAPACITY (AH) of a DP 27 is 100 Amp Hours. C20 (CAPACITY/20) charge rate is 5 Amps. Trickle charge at 0.3% is 3 Amps.
The Capacity AH of DC 31 is 115 Amp Hours. C20 charge rate is 16 Amps Trickle charge at 0.3% is 1.35 Amps. (assuming the three are paralled.)
Charger manufacturers will vary somewhat.
I hope this helps.
Bob

Shelman · Apr 6, 2016

Quote:
"So, in total, I have ... (drum roll) .... 280 AH with a full charge by the "20 AH Rate" standard ... this seems basically reasonable but I have never pressed the test first hand on the true working capacity of these batteries."

Yes it sounds like you are on the right track with a total 20 hour rated capacity of 280ah but since you can only drain your battery bank to about 50% state of charge before you start damaging it and you must limit yourself to the use of the house bank if you plan to save the starter battery for emergency starting in case the house bank is depleted then you only have about 100ah max available for daily use. Actually more if you use it really slowly and less if you use it in a big hurry (Peukert's law). And it also takes a few more amp hours to re-charge the battery than you removed from it due to the waste caused by resistance turning your charge current into heat loss. But your on the right track

I have recently added 150 watts of solar to charge my 420ah bank and have not needed to plug in my shore power charger since. If you have a properly functioning charge controller it is a totally self tending operation. You can even have several charge controllers working at once in concert with shore power charger and alternator and wind turbine. All will play nice together and keep your batteries charged and happy.

And this one has lots of god info too http://www.pbase.com/mainecruising/solar_panel

Here are some shots of my five charge controllers and my five solar panels.

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EMKoper · Apr 7, 2016

Questions and delay tactic!

Nice set-up ... interested in comments on the referenced product but I am generally leaning toward a set-up that has some "charing" ability as well as maintaining so I am having to think about set-up, when the panels go, permanent or permanent, and where to position the regulator (and what regulator is best).

Shelman, ... why the 5 regulators? The only reason I can think is a lower cost install versus the current capacity of one larger (presumably more costly one) with greater current capacity? It also looks like you are only using 2... are the others for growth? Redundancy sounds nice too to account for individual regulator failures.

Questions about a simple solar install and connections to the battery bank (not so complication, just solar charging, no wind or shore power in play) ... I have the three batteries in two banks ("#1" and "#2" on the battery switch or the switch position "#1+#2" which all interconnected)... if I connect the positive/negative leads out of a suitable regulator to any positive/negative battery leads with the switch in the "#1+#2" position, all batteries should be maintained equally, right? This seems simple but there are lots of seemingly ancillary wires and leads and distributors and a thing that looks like a heat sink near the batteries which lead one to believe it is more complicated than V=IR (I'll get a photo of the minor rat's nest next time!)

Finally, I didn't cop out on solar, but bought time to rethink a larger, more grandiose install ... but I did purchase this to charge batteries and provide simple power while on the hard (lights and charging, no A/C or anything like that). Are there any regrets for monitored use of this to charge batteries on a weekend-to-weekend basis? Would not be used unattended and no heavy loads ...

markvone · Apr 7, 2016

Eric,

Yes, the solar regulator will charge all the batteries if attached to any positive terminal anywhere in the DC system IF (and only IF) the main battery switch is turned to '1 & 2' or "BOTH'. With the switch set to "#1' or '#2" if will depend on where the solar regulator output is actually attached in the system and what the wiring paths are.
If you keep the main battery switch on 'OFF' when away from the boat, then you need to consider where the solar regulator needs to be attached to charge the desired batteries.

Using an adapter pigtail to connect your 30A rated boat AC system to a 15A standard outlet should not be a problem. You will only be able to draw 15A before the shore circuit breaker trips.
I usually use one when on the hard to run charger and lights.

I inherited my 55W solar panel from the PO and planned to remove it when I bought the boat. It is located out of the way on a stern rail extension, so I don't notice it (E36RH has a side boarding ladder) and it is very well thought out. My original slip had the stern facing south, so the panel got a lot of sun. It has been five years now and I no longer think about removing the panel. It's nice to have it for keeping the batteries up and saved the day this winter when the old charger died. Finding room for more panel area that is not in the way is the challenge if you desire more wattage.

Mark

Maine Sail · Apr 7, 2016

EMKoper said:
First, I am an engineer and I am good at multiplying units, but understanding the battery "20 AH Rate" and using that information to size a solar trickle charger (non-regulated) has me a little perplexed. Clarity is desired ....

My 3 battery bank is 2x DC31DT house batteries and 1x DP27 Starter ... I would like to understand the size of a solar unit to trickle charge the full bank. From the Deka website:

OK ... I have read that a trickle charge is supposed to be 3% of the amp capacity (more that below) ..

You would be well served to read this article:

Do I Need A Solar Controller?

Shelman · Apr 7, 2016

EMKoper said:
Nice set-up ... interested in comments on the referenced product but I am generally leaning toward a set-up that has some "charing" ability as well as maintaining so I am having to think about set-up, when the panels go, permanent or permanent, and where to position the regulator (and what regulator is best).

Shelman, ... why the 5 regulators? The only reason I can think is a lower cost install versus the current capacity of one larger (presumably more costly one) with greater current capacity? It also looks like you are only using 2... are the others for growth? Redundancy sounds nice too to account for individual regulator failures.

Questions about a simple solar install and connections to the battery bank (not so complication, just solar charging, no wind or shore power in play) ... I have the three batteries in two banks ("#1" and "#2" on the battery switch or the switch position "#1+#2" which all interconnected)... if I connect the positive/negative leads out of a suitable regulator to any positive/negative battery leads with the switch in the "#1+#2" position, all batteries should be maintained equally, right? This seems simple but there are lots of seemingly ancillary wires and leads and distributors and a thing that looks like a heat sink near the batteries which lead one to believe it is more complicated than V=IR (I'll get a photo of the minor rat's nest next time!)

Finally, I didn't cop out on solar, but bought time to rethink a larger, more grandiose install ... but I did purchase this to charge batteries and provide simple power while on the hard (lights and charging, no A/C or anything like that). Are there any regrets for monitored use of this to charge batteries on a weekend-to-weekend basis? Would not be used unattended and no heavy loads ...

I chose to use five separate charge controllers for a number of reasons, the first is that the charge controllers I chose have LED indicators that convey all sorts of information about charging status and battery acceptance, and I wanted to know exactly what each solar panel was doing at all times. The second reason is that I didn't feel like adding blocking diodes to prevent a shaded solar panel wired in parallel from absorbing power from a neighboring panel. And finally I like the redundancy and flexibility of separate charge controllers. (I could always decide to run one to maintain my starting battery ect.) Although I suppose could have saved a few dollars by using just one charge controller I felt it was worth it.
There are several ways to wire in the controllers to charge/maintain your batterys, a few of the most popular options are #1 wire directly into main house bank with a combiner relay between the house and emergency/starter bank. #2 wire directly into your main house bank and use the 1-2-all switch to bleed off power to your emergency/starter bank when needed. #3 route through your 1-2-all switch and be able to chose which battery bank gets power. #4 wire in separate charging systems directly to both battery banks. I chose #3 because I want to be able to have full control over what gets charged and which battery bank I am using. Also This gives me a fully redundant system in the case of a battery bank failure, I simply switch over to the emergency bank and isolate the main bank.
Sorry about the misleading picture I took it while I was installing the charge controllers and I had not finished wiring them in yet.

The shore power cord should be another good tool to keep your battery banks charged up. Keep in mind that your battery charger that pulls power through the shore power cord could also be wired in any of the same ways that I mentioned for the solar panel charge controllers. I have my shore power charger wired directly to both battery banks so that I can keep both battery banks fully charged when at the dock even if the 1-2-all switch is in the off position. I also have my battery banks fused at the posts to prevent damage in the case of a short. Mainsail's website has nice how to articles on this topic too.
And finally make sure the battery charger is not pulling more power than your cord is rated for. The cords can over heat and cause fires with out ever tripping a fuse. I switched over to the smart cord system which includes a thermal shut off in the cord-set to prevent such events.

EGregerson · Apr 7, 2016

panel

EMKooper;
I attached a pic of my panel, a 54 watt kyocera (6 years old) and Morningstar controller (1 1/2 year). I was concerned about the power output (that it was overcooking the batteries); this was from seeing 14 volts on the electrical panel meter. The Morningstar owners manual (which i just re read); says it does that, and more; up to 15 volts in some instances. So, for simply keeping the batteries topped off, a small (10-30 watt panel) (and recommended controller) will do the job. But. If you're out sailing, and running instruments, like depth sounder, knotmeter, vhf radio, refrigerator, stereo, etc; a larger watt panel will keep the batteries up for the end of the day when u want to crank up the motor to head back in (although u could run off the house bank, then use the starting battery later) (In which case, all u really need is the trickle panel). My panel is located under the boom; might be problematic for some but i have long legs, i haven't yet stepped on the panel while flaking the main! 2 cables run from there into the 'stateroom' to the controller; then 2 wires to the battery. Pretty simple really; it's been reliable and saved gobs of diesel when anchored out. ( I have a 2nd 45 watt panel daisy chained when anchored out for a while which really helps). Best of luck, Eric

markvone · Apr 9, 2016

Morningstar ProStar 20 Solar Controller

Eric,

Here is my older ProStar Solar controller. It is an older version of Eric's shown above. From my documentation from the PO, my controller and panel have been installed and operating since 1997 with no issues.

Mark

EMKoper · Apr 9, 2016

Narrowing Down the Questions

Great longevity for that unit ... I see a theme that MorningStar seems relatively solid (seems to be moderately priced so I can see the attraction).

I am starting to fine-tune my questions about controllers and battery banks and this question is about usage of the solar panels not as a "trickle" charger but as a supplement that will also do trickle via a controller (good advice, makes sense, will get a controller/regulator regardless).

I stated a few messages up I have two banks (house and starting) ... presumably I'll use house bank at anchor and it will be depleted sooner and not using the starter to hold in reserve so they will be at different voltages/currents and loads during the day. So my question is that if I use them separately and independently (always want the starter batter to be a little more fresh) do I need a controller with a "dual" battery hook up since the voltage/current to top them off or dump power back into them from the solar array needs to be different? I have read manuals from "dual" controllers and it isn't clear that they are doing all that magic treating them as two separate, independent banks ... do I need two controllers to ensure the banks are treated appropriately during charging or maintaining (trickle)?

Shelman · Apr 9, 2016

You always want a charge controller. So your on the right track there. I would say your simplest solution would be to route the charge controller through the 1-2-all switch and charge which ever bank you select with the switch. Its not the only method, and not the ultimate automatic system perhaps, but it offers you the most control for the least cost and fuss. If you want the "Cadillac" version I would say add a combiner relay which bleads off power from the main battery bank over to the starter bank when the main bank gets full. No fuss and always automatic.

EGregerson · Apr 11, 2016

hook up

I just have the wires from the controller run to one battery of the house bank; i set the selector switch to both. Charges all 3. Haven't ever had a problem.

ps; on the idea of using the house and conserving the starting battery: I try to do that; but i go thru the house bank pretty quick. (the more u have the more u use) Inevitably I use the the starting battery anyway.

EMKoper · Apr 20, 2016

Update and the plan - one question

I have the solar plan ... going with a 25 A controller that can charge two banks independently and going to start with 2x 30 Watt panels. I have planned out the wiring with a little bus bar to combine the panels somewhere after with growth capacity -- the difference in cost for higher capacity UL-1426 was very small.

Question on routing wires from the panels and the run to get under the cockpit ... the panels will be rail mounted on the push-pit and my initial instinct was to drill into the rail, run the wire inside the rail. The difficulty of drilling a hole nicely into the rail tube and then somehow from below through the deck to line up with the bottom of the stanchion mount point might be more work than it is worth (2x, one for each panel and the way to do it properly is likely to remove the pushpit -- more effort than I was thinking). There are no other cable or wire runs around the back of my cockpit to repurpose. Current E35 arrangement (not too many vertical pushpit stanchions):

The next best alternative seems to be something like this (from http://www.pbase.com/mainecruising/solar_panel)... I think I'd include some sort of cable pass through to seal up the point a little more than this, though:

Does anyone have any strong feelings or alternatives? This would be easier if I needed to rebed the pushpit ...

EGregerson · Apr 20, 2016

route

I like the idea of running the wire down thru the gate post. Like u say, drill a hole near the top. But u don't need to drill up from below thru the transom. Remove the little screw that holds the rail in the base; the rail should pull right out (lower the ladder 1st); mine was flexible enuff to get a few inches of sway; then drill down thru the base; might want to remove the base and caulk it (the bases collect water.)

Shelman · Apr 25, 2016

I used a little stainless clam shell and filled it with 3m 4200

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