Electric/Solar Dinghy Up and Running

[mitiempo]

Originally Posted by ski69sail

Hi There

Yes I love your idea. Sounds like a great result from a simple marriage of ideas.
But I was wondering if there is any option to connect to the yachts power via a lead. ???

Thanks Ray

It could easily be done with a lead from the yacht's batteries and a connector like an Anderson or similar. All that is needed on the dinghy's battery is a short lead with the mate to whichever connector you use.

[SailFastTri]

I like it too. Would like it even better with a lighter battery. Perhaps Nimh?

[Wanderlust]

Looks like an interesting project. If you just use it for short trips each day it should work well.

I would suggest making up that charging lead from the mothership. Also, the 50W panel will take quite a while to recharge the battery. Going for a larger panel would be good, but take up a lot of real estate.

In ideal conditions, the panel will put out about 3 amps. But you will not have the optimum tilt, especially when the sun is low to the horizon. So if you have discharged the battery to 50% (1 hour at full speed) it will probably take more than 2 days of full sunlight to charge it. Shadows on the panel will have a substantial effect, and this may be difficult to avoid when nestled next to a pier, or the mothership.

In your first post, the photo shows the panel being shaded by the motor. Can you avoid that?

[Peregrine1983]

Originally Posted by Wanderlust

Looks like an interesting project. If you just use it for short trips each day it should work well.

I would suggest making up that charging lead from the mothership. Also, the 50W panel will take quite a while to recharge the battery. Going for a larger panel would be good, but take up a lot of real estate.

In ideal conditions, the panel will put out about 3 amps. But you will not have the optimum tilt, especially when the sun is low to the horizon. So if you have discharged the battery to 50% (1 hour at full speed) it will probably take more than 2 days of full sunlight to charge it. Shadows on the panel will have a substantial effect, and this may be difficult to avoid when nestled next to a pier, or the mothership.

In your first post, the photo shows the panel being shaded by the motor. Can you avoid that?

Thanks very much. I've got a 100w panel waiting in the wings if this 50w doesn't bring it up sufficiently. The 100w is twice the size, so it would extend over the tubes a bit, but not too bad. The dinghy actually always sits at my dinghy dock with the bow facing south, so the motor is not actually shading the panel right now despite how the photo looks. At 40 degrees N at this time of year the sun is low enough to get under it. However, during the summer a small portion of the panel would be shaded in its present position. I could simply slide the panel forward a bit. I currently have it sitting on top of a large batt box and strapped tightly to the dinghy with zip ties and bungee cords. You're also right that angling the panel to get a better angle on the sun would certainly help charging times. I'll report back on my state of charge after the weekend.

[Peregrine1983]

Originally Posted by ski69sail

Hi There

Yes I love your idea. Sounds like a great result from a simple marriage of ideas.
But I was wondering if there is any option to connect to the yachts power via a lead. ???

Thanks Ray

There surely is, but to be honest, I haven't thought it entirely through yet. I guess I could simply add another lead with quick connector as mitiempo said from the charge controller on the mothership to the dinghy batt. Not sure if there are drawbacks to this. My mothership currently has a 200w system, a house bank of 4 golf cart batts (wired 2x12v) with a victron blue solar controller.

[Peregrine1983]

Originally Posted by SailFastTri

I like it too. Would like it even better with a lighter battery. Perhaps Nimh?

The battery weight is actually not a big deal for me... considering my old 4 stroke tohatsu weighed almost 100lbs. The ultimate system in my mind would be lithium batts, but I was trying to keep this project cheap.

[Orin]

Originally Posted by Peregrine1983

The battery weight is actually not a big deal for me... considering my old 4 stroke tohatsu weighed almost 100lbs. The ultimate system in my mind would be lithium batts, but I was trying to keep this project cheap.

Lithium etc would certainly lighten it up and increase your energy density. Though if you’re not taking long trips I am not sure I even see the point.

A 400 yard trip is under about 3 minutes of run time, so saying you need to run your dinghy 12 minutes a day. Which uses roughly 10% of your battery (10.4Ah) then accounting for some inefficiency you current 50 watt solar system would recharge the system in 4 hours of high sun. Sounds like you could probably get away with less capacity if that was the case. Depends on what you want your range to be I guess. For the type of use my dinghy gets that would be more than adequate, and I would think a great solutions for world cruising.

I would only add aditonal solar if you are going to use it more than 15-18 minutes a day (1000 yard each way round trip) given those numbers pan out.

I was thinking about adding electric power to my dinghy, however if I do I am going to charge it off the mothership... and add extra charging capacity to her.

How many cycles is the battery rated for? What is battery maintenance like for it? That might also hugely impact my battery buying decisions.

[newhaul]

Originally Posted by Orin

Lithium etc would certainly lighten it up and increase your energy density. Though if you’re not taking long trips I am not sure I even see the point.

A 400 yard trip is under about 3 minutes of run time, so saying you need to run your dinghy 12 minutes a day. Which uses roughly 10% of your battery (10.4Ah) then accounting for some inefficiency you current 50 watt solar system would recharge the system in 4 hours of high sun. Sounds like you could probably get away with less capacity if that was the case. Depends on what you want your range to be I guess. For the type of use my dinghy gets that would be more than adequate, and I would think a great solutions for world cruising.

I would only add aditonal solar if you are going to use it more than 15-18 minutes a day (1000 yard each way round trip) given those numbers pan out.

I was thinking about adding electric power to my dinghy, however if I do I am going to charge it off the mothership... and add extra charging capacity to her.

How many cycles is the battery rated for? What is battery maintenance like for it? That might also hugely impact my battery buying decisions.

Here is a $25 dollar battery solution for the tender. 18 ah. At 12 volts plenty for short jaunts .
The panel would recover most of the used ah between coming and going . ( the closer to 50% the better for charging) the closer to charged the less it will accept from the panel. https://www.apexbattery.com/diamec-d...CABEgJBQPD_BwE
Heck for the price get two

[GILow]

Originally Posted by Peregrine1983

Thanks yes this is an important clarification. You'd never want to draw your batt all the way down.

You have an AGM battery so you also want to bring it back to full charge as quickly as possible. Don't leave it a few days even if it has only used a small percentage of its capacity. AGMs die quickly if treated that way.

Other than that, looks like a good project and I am impressed by the speed you can get from a 55lbs thrust motor.

[Peregrine1983]

Originally Posted by GILow

You have an AGM battery so you also want to bring it back to full charge as quickly as possible. Don't leave it a few days even if it has only used a small percentage of its capacity. AGMs die quickly if treated that way.

Other than that, looks like a good project and I am impressed by the speed you can get from a 55lbs thrust motor.

Thanks for the info. My hope is that with the solar system it will always be near full capacity. Yeah, it's a peppy little motor. I'm also wondering how much of my good speed is due to the Takakat design which seems to have a low wetted surface area compared to a traditional rib style dink.

[GILow]

I had a plan to finish my journey down the Murray River in Australia using a home built light cat hull with a Bimini of 1KW of solar panels (borrowed from my house roof) and two trolling motors.

Your post has slightly awakened that old plan, not least because of the Takakat hull design.

[wyb2]

Originally Posted by Peregrine1983

There surely is, but to be honest, I haven't thought it entirely through yet. I guess I could simply add another lead with quick connector as mitiempo said from the charge controller on the mothership to the dinghy batt. Not sure if there are drawbacks to this. My mothership currently has a 200w system, a house bank of 4 golf cart batts (wired 2x12v) with a victron blue solar controller.

We have an eerily similar setup (200 W solar, victron blue, charging 4x 6v golf cart batteries, 60 lb trolling motor on the dinghy with 100 ah FL battery). No charging on our dinghy, we bring the battery on board to charge. Have it wired through blue sea ACR (battery isolator). Breaker is on the main system side - breaker on lets the ACR connect the dinghy battery based on system voltage - breaker off disconnects ACR and dinghy battery from the main system.

The 200 w of solar is not really cutting it (darn fridge), so we only charge the dinghy battery when the engine is running. Will be adding to the solar array soon.

I get a little range anxiety on a longer dinghy rides when fighting a decent wind or current, curious if you actually get 1+ hr at full throttle. I haven't tested my luck that far yet.

[mitiempo]

Originally Posted by wyb2

I get a little range anxiety on a longer dinghy rides when fighting a decent wind or current, curious if you actually get 1+ hr at full throttle. I haven't tested my luck that far yet.

Most seem to have missed my earlier post. A 100 AH battery only gives you 100 AH @ a 5 amp draw. At 50 amps ( what a 55 lb electric outboard uses at full throttle) the battery will give you less than 70 AH. If not going below 50% SOC for battery life that gives you 35 or less AH which is about 40 minutes at full throttle or less.

[john61ct]

Great use case for LFP this. Yes pricey, but 90% usable, lighter weight less space, could put in Pelican case(s) and use for multiple applications, e.g. run tunes for the clambake ashore

[waterman480]

The only issue is that salt water rated trolling motors are about double the cost. Not sure of the lifespan of the fresh water motors in salt water.