How to charge a battery bank a long way from charging sources

[Tomthumb62]

but cant find gas locally for all the money in China.

Ah, that makes sense then. I was comparing your situation to the RV'rs who spend $$$$ to remove perfectly good propane fixtures to replace with electric ones. I mean with enough solar, you could cook for "free", but why ditch a perfectly working solution? Anyways, it makes much more sense if you can't get gas.

 

[Ohms_Cousin]

Ah, that makes sense then. Anyways, it makes much more sense if you can't get gas.

Yep thats it.

I am going to keep my gas setup (well, rebuild it anyway) and keep my 2 gas bottles - I will be able to use either. But once my 2 bottles are exhausted its a 700 mile trip (each way) to get them refilled.

As I said, how I am rebuilding my boat for MY niche use would not make sense to a blue water cruising boat - and thats what this boat was. But I am converting the boat into a specialised platform for my very niche use case. Where I am taking the boat has never been done before - I am starting to realise why. The problem with being a pioneer is you take arrows in the back.

 

[Tomthumb62]

Where I am taking the boat has never been done before

Where are you taking it, if you don't mind me asking? Sounds like an adventure, whatever it is!

Very cool to make it work just how you like for your use case. I have my solo backpacking setup. I've tailored it over the years and it's such a joy to go on trips where every piece of gear I know how to use, know when to bring (or not) it and only carry what is truly necessary. For example, my umbrella comes on every trip, rain or shine. Shade in the sun and nothing like NOT wearing a rain jacket while hiking uphill but staying perfectly dry under the 'brella. Anyways, you'll have to put a thread in the Show and Tell section when you're done.

As for arrows in the back, if you're referring to the other poster, sounds like they're just a bit cranky. I have no idea if your 'run amps from stern to bow' is actually going to cost you tens of thousands, but it does seem be an awfully high number. Thousands I can see, but tens of them? But I literally have no idea the costs of boats other than they can be rather expensive.

 

[Ohms_Cousin]

Where are you taking it, if you don't mind me asking? Sounds like an adventure, whatever it is!

As for arrows in the back, if you're referring to the other poster, sounds like they're just a bit cranky. I have no idea if your 'run amps from stern to bow' is actually going to cost you tens of thousands, but it does seem be an awfully high number. Thousands I can see, but tens of them? But I literally have no idea the costs of boats other than they can be rather expensive.

I sent you a PM about where etc. Dont want to the world to know where to find me.

Yeah our friend came off as a bit narky for sure - forums are full of it. Luckily this forum is mostly good regards that sort of thing.

It most certainly would not cost tens of thousands but it would be expensive and clunky to run very very thick DC cables around the boat. Plus all the DC switch gear which is not only expensive but large as well. Rather keep DC runs to a minimum where possible.

As I have said, I am not sure if my approach is sensible or not, hence posting it here to be picked apart. What could I be missing ? Hopefully if I am missing something someone here will let me know.

In the end it will all be designed by my sparky. But as i said i have to take my ideas to him to build it out. Its hard to find a creative thinker for hire in the electrical field.

 

[Tomthumb62]

hard to find a creative thinker in the electrical field.

I spent weeks thinking and dreaming about what amounted to be quite a simple electrical system for our little camp trailer. I had my own ideas/desires and my wife had hers. Hers had mostly to do with aesthetics, which I can appreciate, but sometimes doing it her way was the most difficult or time-consuming way to do it. Lol. Anyways, I could see being a sparky to just want to follow someone's plan...tell me what you want and I'll wire it together, but having to come up with the design of it all I can see is a special skill.

For example, I wanted to improve our AC connections:

• A manual switch to switch AC power source from INVERTER-OFF-SHORE. I found such a switch, it was cheap, but exactly how to wire it up kept me up at night.
• Another 120v plug for the AC battery charger to plug into. Not to be switched on or off, but would power up and start charging anytime we plugged into shore power.
• Adding two AC outlets.
• Wire to run everything and how much.
• A 20A circuit breaker for the AC loads.
• USB dual port charger for phones and other things
• All this to fit in a very tiny space AND it had to look good (my wife actually came up with the best solution to that).

I guess the creative part not so difficult (except for the nice part my wife built), but where it crosses over in the technical details of how to wire it all together was what kept me up at night figuring out how to do it all. In the end, I learned to love wire nuts. Using the correct size wire nut for the number of wires joining is cheap and very strong. In the end I think I had a mess of about 20 wire nuts. All the ugliness of that is hidden away behind a panel (thanks to my wife).

Good luck, I do look forward to your solutions. Lemme see if I can find the thread from today that talked about converting DC to AC for running longer distances.

 

[Tomthumb62]

This isn't the exact thread I was looking for, but it's very similar, maybe there are some ideas for you in it:

Planning for PV Expansion - looking for some advice

I am looking for some input: Feel free to make suggestions or point out my errors. I am planning a new barn for the property, this could also supply a suitable new area for some new PV to mount. For now, I am looking at 16 more 440 CS panels (like the ones I already have), and combined would...

diysolarforum.com

 

[Rocketman]

I think you are on the right track on having a battery charger being ran by the sterns inverter. (You could do the same going from front to back - that way you can transfer power to the rear battery).

Here are a few more items to think about (make sure your design solves them).

The two batteries will be at different states of charge, you will need a different bms for each of them. (That way if the front ones gets too low, and needs to be cutoff for discharge, the rear one still runs).

The two inverters will not be in sync - thus their power cannot be blended, if one goes out, how to power that part of the ship from the other . Maybe have a run of AC wires from the other inverter that terminates near the inverter and then pull the dead inverters AC1 out wires and tie them to the other inverter. (Make sure you document how to remove the inverter- trying to figure something out when stressed by a problem causes mistakes).

Remember to label all wires as you install them on both ends (and document),

I wish you luck! I like unique projects and will be following yours!

 

[Tomthumb62]

The two inverters will not be in sync - thus their power cannot be blended, if one goes out, how to power that part of the ship from the other . Maybe have a run of AC wires from the other inverter that terminates near the inverter and then pull the dead inverters AC1 out wires and tie them to the other inverter.

Or wire in a manual AC switch (this is what I did), that allows you to switch between power sources. A 3-way (or 4-way, 4th position is OFF) switch could do this:

Position 1: power in from Inverter #1
Position 2: power in from Shore power
Position 3: power in from Inverter #2

I just did something like this in my trailer and it works very well. I would NOT do this for DC loads (I don't trust them unless they're $$$$, unless there is no current flowing), only AC.

I guess it depends upon the sizes of these inverters and at what voltage/amps they are rated for. Quality switches like that could get expensive if it's high powered.

 

[Ohms_Cousin]

@Rocketman - you are right - a standalone AC battery charger in the Stern could move energy from the front battery bank to the rear battery bank in the same way the bow standalone AC Battery charger moves energy to the front battery bank from the rear battery bank. This transfer of energy can only done by AC chargers it seems (unless there is another way that I have no clue about at this time).

It CANNOT be done via DC UNLESS both batteries are at the same or almost exact same voltage - otherwise there is a MASSIVE INRUSH of current that would trip all the safety devices or burn the cables - it could be thousands of amps depending on the voltage of each bank. If both batteries are at the same or almost same voltage then what would be the point of transferring energy between them?

So it has to be an AC transfer method and standalone battery chargers are the only way I can come up with to do this. It cannot be the AC OUT of one inverter feeding the AC IN of another inverter.

I think we have this right in the sense explained above.


By having a standalone AC charger at each end of the boat, energy from each big battery bank can be transferred up and down the boat as may be needed. If the BMS on the stern battery bank trips, the front battery bank is still operational and Vice Versa. So that all makes sense.

I would think that an Automatic Transfer Switch of some kind would be the way to wire this up (and this is where the sparky does come in) so that if one of the inverters fail the other would be switched to automatically,

The whole logic of this thread is to make sure there is enough energy in the battery bank connected to the inverter (at either end, but the stern is easy since it is close to DC charge sources) so that when that Inverter is called upon to power an AC circuit there is indeed enough energy in that battery bank to make sure that AC circuit is powered up correctly.

There are going to be a number of AC circuits going from back to front and back again to wire all this up. However thats the benefit - its AC and the wire sizes are very manageable - we are only moving approx 5kW of AC energy 15 mtrs at most.

Definitely food for thought and worth chasing up a bit more. I think I need to go to logical diagrams next.

Been doing a ton of reading the last days trying to figure this out. Seems those Winston batteries might be the right choice for up front in the bow area- they are built very VERY solidly. I could use the EVE 304aH cells back in the stern area were everything is well protected and solid.

 

[Tomthumb62]

It CANNOT be done via DC UNLESS both batteries are at the same or almost exact same voltage - otherwise there is a MASSIVE INRUSH of current that would trip all the safety devices or burn the cables

This is what DC-DC chargers are for, but I'm not sure how they work in your situation or if even if such large enough of them exist (other than putting many in parallel operation. But probably a moot point simply due to cost/weight of such large DC cables, fuses, switches, etc. But correct, you would not just wire up two batteries and let 'er rip till they balanced out, you need an interface such as DC-DC charger(s).

It cannot be the AC OUT of one inverter feeding the AC IN of another inverter.

It doesn't work this way. Because the IN of such an inverter is a DC source. It outputs AC but only accepts DC. Not sure what would happen if you tried to connect an AC source to an inverter, but I can't think it would be good.

 

[Ohms_Cousin]

I think you are on the right track on having a battery charger being ran by the sterns inverter. (You could do the same going from front to back - that way you can transfer power to the rear battery).

I think you are onto something with that approx !

Here are a few more items to think about (make sure your design solves them).

The two batteries will be at different states of charge, you will need a different bms for each of them. (That way if the front ones gets too low, and needs to be cutoff for discharge, the rear one still runs

Yes a BMS on each battery is the only way to do it. This brings in another level of redundancy.

The two inverters will not be in sync - thus their power cannot be blended, if one goes out, how to power that part of the ship from the other . Maybe have a run of AC wires from the other inverter that terminates near the inverter and then pull the dead inverters AC1 out wires and tie them to the other inverter. (Make sure you document how to remove the inverter- trying to figure something out when stressed by a problem causes mistakes).

An ATS (Automatic transfer switch) of some kind would probably be the way to go here.

Remember to label all wires as you install them on both ends (and document),

I wish you luck! I like unique projects and will be following yours!

Thanks for your well wishes - this project is going to take every ounce of grit I have in my DNA !

 

[Ohms_Cousin]

What I am trying to convey here is that the AC output of an inverter should not be used to be the AC source in of another upstream inverter.

For example lets take a Victron Quattro Inverter. It has 2 AC inputs - either Grid and Genset or two gensets (dont see why it couldn't be 2 AC inputs - an example is here on the farm where I am - we have 2 grid feeds - one is agricultural tariff for powering the farm workshop, water pumps etc and the other grid feed is for residential at a much higher per kilowatt rate - both grid feeds come in through different transformers - so why couldn't the Quattro use the 2 AC grid feeds in ? ). We have had the situation where the workshop is UP but the houses are DOWN - if we had a connection from both transformers into the Quattro, when one grid feed is down the other would power the inverter - but I digress......

So the Quattro has 2 AC feeds in and 2 AC feeds out. What I am trying to say is one couldn't use one of the AC outlets from the 1st Quattro to be one of the AC feeds in on a 2nd Quattro. I dont know why but I have read this is not allowed by Victron.

As for DC - DC chargers - yes the output is way to low. They would have to Multiplied in parallel and as you point put then all the DC cabling issues come back and have to be dealt with. DC has its uses but this is not one of them.

 

[Tomthumb62]

My apologies - I've only dealt with simpler DC to AC inverters, not these combo units that can combine DC and AC sources in one like the Multiplus and Quattro. Sorry about that. I gotcha now.

 

[HarryN]

Here is a fairly in depth thread on 48 volt chargers in case it is helpful:

Looking for 48V Battery Charger

Does anybody have a recommendation for a battery charger for a 48V LiFePo4 Battery Bank (~ 2000 Ah , ~ 100 kWh) ? I need to use it to "fill the gaps" when the sun is not shining. Something like several x 2kW each or a big ~ 8-12 kW unit (3-phase). For use in Europe 230/400V grid :) .

diysolarforum.com

The one caution about the dual inverter / chargers is that they can be finicky about the incoming power quality and frequency consistency. If it isn't tight enough, they won't sync up and couple together. I have personally seen this happen.

Most dedicated chargers are very tolerant of incoming power quality. Some are 50 / 60 hz and can provide substantial isolation of the boat's electrical system from the shore electrical system / surges, etc.

 

[timselectric]

Late to the conversation. So hopefully I don't repeat others suggestions.
AC is definitely the way to move power over long distances.
For redundancy, two systems is definitely the best way to go. And 48v nominal makes things easier.
I would install two AC circuits between the bow and stern. With a chargeverter in both locations. This will allow for up to 100a of charging current in either direction. And from multiple sources. Including shore power.
I'm assuming that you will be balancing your loads across the two systems. Based on their location on the vessel. But this will also allow one system to help the other if needed.
There are a lot more details to think about. Like if one system goes down. And the other needs to carry all necessity loads. But this is just the basics of the design.

 

[wholybee]

I've not read the whole thread, so hopefully I didn't miss something important. Some basic questions. You are planning a 42' sailboat(not that large), with a very large 48V battery in the bow, charged at 200A. How are you planning to generate 200A at 48V? That is like $7000 worth of alternators on the diesel (qty2 100A 48V) My first thought is that maybe charging at 50A is reasonable.

You say you want the weight up front to balance out weight in the back. How much and what weight in the back? The electric pods are a couple hundred pounds I would guess (about the same as a single crew member) but underwater with some buoyancy, so not much of an impact I would guess. The worst place for weight in a sailboat is on the ends. Maybe you are not adding as much weight as you think, and maybe moving the batteries aft a bit, under a settee or in the bilge, would have the weight far enough forward and shorten the run.

AC introduces safety issues and a large transformer at each end will add even more weight and require more space. I am trying to imagine where you might install a 3000W inverter in the aft of the boat (and a battery because you don't run it direct from an alternator) and a 200A 48 volt charger in the bow. It just doesn't make any sense to me, and isn't going to be any cheaper than spending thousands of dollars on heavy cable.

Have you worked up an energy budget? Electric cooking doesn't actually take that much. Electric propulsion does, but if you have to burn diesel to charge, then just use the diesel to propel the boat. And it *IS* a sailboat? I am thinking a 10kW battery might be adequate for your use case. That would be more than enough for an electric galley and anything else domestic, and would give you a bit of electric propulsion before you need to start the diesel.

 

[Tomthumb62]

Electric propulsion does, but if you have to burn diesel to charge, then just use the diesel to propel the boat.

Not OP but we got into a private exchange and I can assure you, these electric propulsion pods are essential to his mission. Diesel or sails aren’t going to cut it. Also, diesel and propane is difficult to acquire where he is, but there’s plenty of sunshine.

 

[wholybee]

Not OP but we got into a private exchange and I can assure you, these electric propulsion pods are essential to his mission. Diesel or sails aren’t going to cut it. Also, diesel and propane is difficult to acquire where he is, but there’s plenty of sunshine.

So, he plans enough solar panels to produce 200A at 48V on a 42' monohull? Not gonna happen. Which circles back to maybe 50A of charging is enough.

Not knowing all the details of his situation, but given the complexity and cost of his proposal, maybe selling this boat and fitting out a catamaran electric would work better and not be any more expensive. More room for solar, easier to distribute weight, easier to split battery bank for redundancy, etc. His plans on a 42' mono I think might be a money pit that never works as he needs it to.

 

[Tomthumb62]

So, he plans enough solar panels to produce 200A at 48V on a 42' monohull? Not gonna happen. Which circles back to maybe 50A of charging is enough.

Not knowing all the details of his situation, but given the complexity and cost of his proposal, maybe selling this boat and fitting out a catamaran electric would work better and not be any more expensive. More room for solar, easier to distribute weight, easier to split battery bank for redundancy, etc. His plans on a 42' mono I think might be a money pit that never works as he needs it to.

I know zilch about boats but know they’re generally a money pit. And from what I gather he might be already in too deep to detour.

 

[SparkyGage]

A few thoughts and questions:
1. Can you post the make and model of the boat so we can see a layout?
- Where are you planning to mount the solar panels: hanging off the stern, wrapped around the stern and sides, as a canopy over the cockpit, etc?
- Keep in mind, you are going to get about 15wt per square ft of solar on average. Big residential panels can sometimes hit 20wt/sqft but I haven't found a portable that calculates better than 15. The BEST wt/sqft panel I can find a the moment is 83inX41in and rated at 455wt. That would be 3kwh at 7 hours of ideal sun. With 2 to get the voltage up, you are looking at just shy of an 8'x8' square and that's for rigid panels.

2. Considering your loads, are you likely to deplete the battery bank in a day (ie 90% of 30+KWh)?
- are you running AC or DC appliances?
- are you running an air conditioner?
- are you powering the pods from the front battery bank or is it backup to the rear bank?

3. If you are looking at 14 days on a trip, and you figure to return to port with a minimum of 10% reserve, you need to calculate maximum daily usage (worst case). If you are using 3Kwh a day and can recover 1.5Kwh from solar and generator.
- I'm guessing you plan to use diesel in heavy seas and currents and electric in sheltered waters and moorings?

4. Diesel Charging: You said 48V Alternator, but I think you mean GENERATOR that could be mounted on the diesel engine. 100A (4.8Kw) models are the same basic size and configuration as a heavy duty 12V Alternator. It would be about a 6hp drain when running.

5. Alternative Charging: If you are converting DC to AC then back to DC, you are going to have a 10% loss at minimum under ideal conditions. I would think 20% would be more likely. With a 3/0 cable DC you are looking at a less than 1% loss over that 45 feet. Boosting the charge of the front pack from the GENERATOR on the diesel engine would not be an issue for that distance.

6. Battery bank with the cells you are talking about: So based on the cells you mentioned, you would need 16 cells at 5.5Kg for 14KWh so that's 176Kg for 28KWh, or just shy of three AGF or four ISM (AGF= American Girl Friends, ISM=Italian Super Models). This doesn't strike me as a lot of weight overall in a boat displacing 15000lb?

I hope you can make this system work for you. Looking forward to seeing it play out!

And to the naysayers: Yes, boats are money pits, but so are RVs and sports cars. But you can't stand on the side of the road waiting for AAA if something breaks. And boats are more complicated the bigger they get. Not learning and having a first hand understanding of the systems of YOUR boat that you take on the ocean is SUICIDE. He needs to be able to disable, take apart, repair and replace any critical system on the boat. And even if he can't repair part of it, he needs to be able to explain to someone that can EXACTLY how it ties in with the rest of the systems.