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Old 03-12-2021, 07:01   #1
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Join Date: Sep 2020
Location: Caribbean
Boat: Custom 47' Wood Epoxy Cat- Alcazar
Posts: 24
Build thread: 24v system from scratch

Hello everyone,

After a lot of lurking and learning I think I can hopefully help some people by documenting and sharing my own experiences rebuilding my boats electrical system from nearly scratch.

I will break down where I started and where Iím going and hopefully someone in a similar situation can perhaps benefit from my shared experience.

Before we go any further, I would like to disclaim that I am NOT qualified to give advice on marine electronics. In fact I have very little experience at all; anything I say is just what I say, it carries no authority and you use this information at your own risk.

I would like to share more useful things like a wiring diagram, but I donít have a computer and am doing everything from my phone currently. I donít really have the means to make one at the moment.

The boat is a 47íft cat, slim-ish hulls so weight is a important consideration.

The boat is new to me and this is my first major upgrade. The existing electrical system is functional and would perhaps be sufficient for modest needs. I often have 7 or 8 crew aboard and plan for a watermaker so more power is a must. The existing batteries do not seem to pull their rated capacity.

Here is what we currently have onboard:
6 x Trojan T105 Golf Cart Batteries
4 x Siemens 75 watt rigid panels
Morning star 20 amp charge controller
Super wind sw 350 windgen
Synergex 1500 watt 220v inverter
Victron Centaur 12v 80 amp battery charger
2x Victron Cyrix 12/24v 120 amp battery connectors (allows alternator charging)
2 start batteries for the engines
1 working 85 amp alternator
1 non functional 85 amp alternator
12v DC breaker panel and distribution which powers everything (Nav/fridges/windlass contacters/lights)
220v distribution to existing outlets in each cabin.
2000 watt Yamaha portable generator

The system works, we are not uncomfortable, however I can only run a single fridge 24/7 and the batteries are ALWAYS low. Future Nav improvements, a second fridge, and a watermaker would never work on the existing system. The only things I plan to keep are the Yamaha generator, start batteries and alternators, and 12v and 220v breaker panels and distribution (for now).

When planning the new system I did not bother with trying to measure my needs and appropriately size the new system. I simply decided to go with as much solar and battery capacity as I could reasonably fit without breaking the bank or overloading the boat. I figure I can add more if necessary later, and with more experience I will make better decisions.

So, thatís what we have and why it has to change. In the next post Iíll break down my plan for the new system and my costs for each component.
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Old 03-12-2021, 07:06   #2
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Boat: Custom 47' Wood Epoxy Cat- Alcazar
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Re: Build thread: 24v system from scratch

On to the new system.

I decided on a 24v (battery voltage) system for a couple reasons. First, it makes all the individual components (charge controllers, inverters) cheaper. Second, it reduces necessary wire diameter, therefor saving costs and weight. Third, large loads like the watermaker motor and the windlass motor should be a bit happier at 24v. This is what I have read but I am not an expert.

I decided to go with LifePo4 batteries because they weigh less, offer more usable capacity, and depending on where you source them can actually be outright cheaper than lead acid when comparing equivalent usable capacity. I ordered 16 280ah 3.6v cells from Aliexpress. They were cheap but the jury is out on how quality they will be.

I will build them into individual 12v batteries each with their own BMS and then wire them into a 24v battery bank. I went this route for redundancy; if I had an issue with one of the batteries or the bank, I could still disconnect them into the 12v batteries and use them to jury rig a functional system or start an engine.

I ordered 4 build kits from SunFunKits, including the 150 amp BMS. This should make putting them all together quite easy and perhaps fun.

For solar panels I decided to take a different route than most and purchase CIGS panels. CIGS stands for copper indium gallium selenide. These panels use a different chemistry than typical silicon based panels, and as such they have different properties. To start, the panels are made from a thin continuous film of the PV material that is usually mounted on a flexible substrate; meaning unlike silicon wafer based panels they can actually flex or be walked on without risk of damage. They can be rolled for storage without damage. They are still very lightweight and low profile.

Because they are not individual cells and are instead a continuous film, they have many many many Ďbypass diodesí (I am not sure they are actually bypass diodes in this case). This means they handle shading extremely well. In my tests with a single 50W panel, shading any percentage of the panel would result in a similar percentage of decreased output. The orientation or area of shading is not important, meaning a boom hanging over the array will not kill the whole output, and will instead have a minimal effect on output, proportional to the area it shades.

Performance while partially shaded was a big motivation in selecting these panels as it is my hope they will still perform well when sailing. Only time will tell but I will happily share my results.

Weight was also a large consideration.

Unfortunately the only CIGS panels I could cheaply get my hands on are 50 watts from a company called MiaSole, via Amazon. They cost about $86 US each shipped. I will simply use a lot to build a sizable array (I hope to fit 28 panels on the Bimini). I tried contacting multiple CIGS manufacturers and could not get a hold of a single one to order larger or custom panels. I will start with an 8 panel install and test for performance before ordering more.

For the rest of the system I decided to go with Victron products because I have worked with them before and trust their quality.

The following is a list of components purchased for the new system and prices including shipping to Miami. Everything was purchased from Amazon unless noted otherwise.

16x 280 Ah cells from Alibaba ~ $2000
4x 12v battery box and BMS from $1350
Victron Multiplus 24/5000 - $2054
Victron Cerbo GX/Touch 50/Smart Shunt- $650
3x Victron charge controllers 100/20 - $500
28 CIGs panels - $2400
Victron Orion 70amp 24/12 - $141

Total major component costs, not including wiring or fusing: $9100

Not as expensive as I had predicted, for what will hopefully be a powerful system that allows for high AC loads like induction cooking.

Almost everything is already on the cargo ship to St Maarten. I should be there by the end of next week at which point I will collect materials and begin the switch over.

Next post will talk about challenges switching to 24v.
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Old 03-12-2021, 07:09   #3
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Re: Build thread: 24v system from scratch

In switching to 24v, I faced two major downsides. First, my alternators are cheap, dumb, 85 amp, and cannot be simply connected to charge the house bank as they could before. Second, my windlass is 1200 watts @12v, and can sometimes draw huge current.

For now I have decided to abandon alternator charging completely and just wire the alternators to the start batteries. This means I wonít get any power when motoring for the windlass or Nav equipment, and I cannot simply start an engine as a means of charging the batteries.

I chose this route for a few reasons. First, itís much simpler. The new installation will use much less heavy cable and will essentially behave like the charging system in a car, meaning it will be easy and cheap to fix and maintain anywhere. I will eliminate several heavy cable runs and hopefully save a bit of weight.

Second, I almost never use my engines, and I would prefer to never use them at all. My boat sails well in light winds and I am not in a hurry. I understand the engines will be necessary sometimes (Iím not converting to EV), but I think thereís a chance I can get away without alternator charging.

As a backup I still have the 2000 watt portable Honda generator to charge the batteries through the multiplus.

Sourcing a new 24v motor for the windlass was around $500 usd shipped. A completely new factory assembled 24v windlass is $1300. My windlass is old, but works just fine and I could probably sell it for a few hundred dollars.
It seems to make more sense to just buy the new one and deal with a windlass swap than save a few hundred dollars and still deal with a motor swap. In the end itís more expensive but I have a brand new windlass. For prices I am looking at

So, thatís it for now. I will update the thread as I do the install and continue to report results and my thoughts/reviews of the components I chose.

I welcome any feedback, suggestions or questions!

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Old 08-01-2022, 14:40   #4
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Boat: Islander 36
Posts: 1
Re: Build thread: 24v system from scratch

Hi Jagarwal,

I'm embarking on a similar installation to you - (I've been asking questions mostly over on I am redoing the electrical on our 1976 Islander 36 which is mostly all original. Cells are out of China (building our own battery), and a majority of victor components. I was going to upgrade the alternator from the stock 40Amp but have decided to invest that into Solar instead.

I'm really curious about your CIGS panel. and experience so far. I get this is very new for you still so probably not much to comment on. It would seem one of the main manufacturers was building them for roofing an such they are all 7 feet long! I looked like you and can find a bunch of 'gone out of business' panels on eBay but again all too long. I am interested in their flexible nature and their ability to tolerate shade more (which may be due more to manufacturing than CIGS themselves)

We don't have the funds for an arch for the Islander right now (would only do custom), and have no Bimini currently. We are having the pushpit re-fabricated, and so a Bimini might be an option, but that also opened up the idea of solar on the sides of the push pit that could be adjustable (and rigid).

I don't mind paying more for CIGS if it means I cut down on the supporting structure cost. The Islander is a beautiful boat and we do have some priorities around keeping nice lines and so giant rigid panels are not our preferred option.

I'm looking at perhaps adding two bars across the top of the dodger that would mirror the shape of the dodger (convex) and then I could mount flexible panels to them (perhaps adhered to a substrate). This would allow airflow, and prevent hot spots on the dodger and possible fire hazards.

How are these panels working for you? How is the build quality? Have you done any testing? I would love to hear about them. The alternative I was looking at was Rich Solar, with a single 160w panel that is about 5' x 2'. Also the ones you found on amazon do not ship to Canada.
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Old 09-01-2022, 03:06   #5
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Location: Aussie East Coast
Boat: Looking now. Proud AP sailer
Posts: 47
Re: Build thread: 24v system from scratch

Interested in how this progresses.
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