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

[Ohms_Cousin]

I am trying to figure out how to charge a battery bank in the bow of a sail boat. The charge sources are at the stern of the boat (as I guess most charging sources would be in a sail boat).

The battery bank up front would be around 30-40kWh at 48vnom. The DC cabling should support up to 200 amps of current. To run a DC cable from the stern charge sources to the bow battery bank would be about 15mtrs of cable each way, so a 30 mtr run of DC cabling. Not really very practical.

It seems that an AC source to charge the bow battery bank would be best. I am thinking that perhaps a Victron AC charger up front close to the battery bank would work. So that means I would need to run an AC cable set from the stern to the bow. Is there any reason I couldn't power the AC charger up front from a Victron inverters output in the stern?

I plan on putting an Inverter up front fed from the batteries up front as I want to have 2 inverters onboard for redundancy.

Early days on this thought, so before I go to far wondering if powering an AC charger up front from the output of an inverter in the stern makes sense I would like to hear your thoughts on the pitfalls of this type of setup. I am sure there are issues here I am not thinking about.

I would think its very inefficient for one, what with the losses involved in inverting from battery in the stern to send AC to a charger up front to turn the AC back to DC to charge the front battery bank. Then the battery bank up front powers the Inverter to turn it back to AC. Got to be horrible losses involved in all that.

But how else can one charge a large battery bank with DC charge sources when the battery is a 30 mtr total cable run from the charge source? Sure massively thick cables are one way, but it is that practical ?

 

[Tomthumb62]

EDIT: Ok, clearly my maths were way off, so you can ignore what I wrote below this. Gonna need a bigger boat to haul all the cash needed for such a build, lol.

Not one of the resident experts here on the forum, but my guess is I think you're on the right track by running 120V wires via inverters and AC chargers (smaller gauge/cost and WEIGHT) than trying to do DC. AFAIK, your main loss will be at the inverter. Victron inverters are all quite efficient, I think most/all of them are 90-92% efficient, so a 10% loss at worst.

While yes long thick DC cable runs would be the most efficient in term of energy, the sheer cost of such thick copper cable is crazy. Not to mention the added weight to a boat. My voltage drop calculators don't go past 120mm^2, so I am extrapolating that to get a 3% voltage drop, you'd need 185mm^2 aka 350MCM (two sizes thicker than 4/0 AWG). 200 feet (90 feet x2 for each leg of the circuit, plus 20 feet extra because it surely won't be a straight line!) of 350MCM stranded copper (do they make a marine grade tinned version?) will run you $1700USD (plus freight would probably be hundreds more). Note that I simply came up with the first google listings not necessarily the best price. By comparison, 200 feet of 10/3 wire would be about $600USD, but you might need more than one run to get your 200A of charging power. And maybe 12/3 is good enough? I'm no electrician and I might be totally off in these calculations, but I can't see how the weight and cost of massive DC cables would make sense here.

 

[Ohms_Cousin]

yep - my thoughts exactly. Plus the cost of the DC breakers needed to protect the DC cabling for that run - it adds up real fast.

Wouldn't need 200 amps of charging at AC level (and couldn't generate that much anyway) - the 200 amps is just the DC load max that would ever happen.

 

[Minnichds]

This is an 800Ah bank correct?

I ask because that sounds big and before I am able to dive deeper it would be helpful to clarify. If I’m correct, you need to hire an engineer and quit freeloading.

Edit.
Let me clarify. The sheer cost to this in DC will put most people a few months rent back in cost. To do this in AC will put most out slightly less, but you want to add into the equation another inverter up front, anyway you add you run AC and DC up front. Check the prices on an inverter charger up front sized to charge that system and compare that with the cost of a spool sized and rated properly.

You are getting into the tens of thousands here likely. You are not an electrician or an engineer? Do you really trust yourself with an install in that range with all of the proper safety precautions taken?

 

[Ohms_Cousin]

This is an 800Ah bank correct?

I ask because that sounds big and before I am able to dive deeper it would be helpful to clarify. If I’m correct, you need to hire an engineer and quit freeloading.

well thanks for your positive input Minnichds.

It has nothing to do with freeloading and everything about forming ideas BEFORE going to sparky. Being able to have an intelligent conversation with a sparky saves everyone's time. Sometimes there are ideas hatched on here that the sparky may not come up with.

There are many useful ppl here on the forums who are happy to share thier knowledge and experience. Clearly you are not one of them.

**Edit**

I have no intention of doing final design myself. My intent is to brain storm ideas to present to my local sparky. He is a busy man and wont have time to sit with me and think up all the possible ways to do something. Intent here is to understand the how's and whys and why things will/will not work. Then from that present ideas to my sparky. The other issue is that not everyone keeps up to date and current with the newer ways/ideas/ equipment out there. There is a wealth of knowledge here on the forums and there are some damm smart people here among us. Having a friendly chat about possible ways to skin this cat is appropriate. If anything I came up with did not sound safe or doable, then in the first instance many here would point that out and secondly the sparky would never sign off on it. My sparky is an industrial electrician who installs and sets up PLC's who also happens to have a boat at the club. Being an older guy he wont know every latest thing out there about Inverters and LiFePo4 batteries on boats.

So whats wrong with asking here ?? - since you obviously took offence that someone who is not an electrician would dare to ask such a question. Are you an electrician who feels that we may take work away from you? If not then I dont understand your stance. In fact even if you are a marine sparky, I still dont understand your stance. No one was born an electrician and everyone learnt about it somewhere at sometime.

 

[Minnichds]

well thanks for your positive input Minnichds.

It has nothing to do with freeloading and everything about forming ideas BEFORE going to sparky. Being able to have an intelligent conversation with a sparky saves everyone's time. Sometimes there are ideas hatched on here that the sparky may not come up with.

There are many useful ppl here on the forums who are happy to share thier knowledge and experience. Clearly you are not one of them.

I edited, I starting doing the math and became appalled at the sheer cost to doing any of it. I assumed you were a millionaire yacht owner from old money.

 

[Minnichds]

well thanks for your positive input Minnichds.

It has nothing to do with freeloading and everything about forming ideas BEFORE going to sparky. Being able to have an intelligent conversation with a sparky saves everyone's time. Sometimes there are ideas hatched on here that the sparky may not come up with.

There are many useful ppl here on the forums who are happy to share thier knowledge and experience. Clearly you are not one of them.

You will need a big ass spool to run either AC or DC, this is in the thousands range. A crimp that size runs into the thousands. An inverter that size well in the thousands. And your batteries are also in the thousands. Do you understand how many fires I’ve seen from improperly sized and crimped equipment? If this is going out to sea this conversation might save your life. An electrician would be the only person qualified for an install like this and an engineer would be the only person qualified for an install of this. I wouldn’t recommend you perform this install if you haven’t priced out all the items to see that the capacities alone are talking pretty dangerous levels.

Running 48V would be safest for this, doing it properly is something that you make too much to do yourself. Unless you are an electrical engineer, if you are, then you are likely not on a forum asking how to do so.

 

[Ohms_Cousin]

I edited, I starting doing the math and became appalled at the sheer cost to doing any of it. I assumed you were a millionaire yacht owner from old money.

None of your assumptions are correct. It just seems a strange way to barge in on a thread. I see you have 4 posts here and not been a member that long. You will find that this is a friendly place and lots of people here are happy with chatting about these types of things.

Lets just move on and think about how to move energy up and down a sail boat from stern to bow and back. DC whilst the most efficient has lots of issues attached to it. Seems like AC is the way to move that energy that far.

One thing about my setup is I need to get some weight up front to balance out all the weight going in the stern end of the boat. A big battery bank is perfect for this (another way is 200 mtrs of 10mm chain in the anchor locker, but rather get the advantage of more power onboard)

 

[Ohms_Cousin]

You will need a big ass spool to run either AC or DC, this is in the thousands range. A crimp that size runs into the thousands. An inverter that size well in the thousands. And your batteries are also in the thousands. Do you understand how many fires I’ve seen from improperly sized and crimped equipment? If this is going out to sea this conversation might save your life. An electrician would be the only person qualified for an install like this and an engineer would be the only person qualified for an install of this. I wouldn’t recommend you perform this install if you haven’t priced out all the items to see that the capacities alone are talking pretty dangerous levels.

Running 48V would be safest for this, doing it properly is something that you make too much to do yourself. Unless you are an electrical engineer, if you are, then you are likely not on a forum asking how to do so.

What I would say to that is, it is what it is. I need the power from as large a battery bank as I can fit onboard. I like the idea of redundancy - plus out here we live by the motto - 2 is 1 , 1 is none. Out at sea that is especially true. So having two battery banks and 2 inverters is a nice redundancy plan. But how to charge that battery bank up front far away from the charge source? Charging will be by alternator/DC genset/Solar panels - all sources of CURRENT. Moving that DC current 15 mtrs from the stern to the bow is challenging and not just cabling. One has to think about all the safety gear that goes with it - DC fuses/CB's/Contactors etc.

Seems its far easier to do in AC then DC. But i stand to be corrected. I know there are some horrible losses in going DC (charge source) to AC (inverter) then AC (charger) to DC (batteries) then DC (batteries) to AC (inverter) again.

One way to do it would be to use the output of the 1st inverter (so AC out from inverter 1) to provide AC in to inverter 2 and then use the onboard charger of inverter 2 to charge the batteries upfront. However as I understand it, its not advisable to power an inverter from an inverter, hence proposing sending AC out from inverter 1 up to a standalone AC charger to charge the battery bank up front. Then the front batteries send DC into the inverter up front. This is about the only way of using AC to charge the batteries up front without using a genset up front or having a shore power connection up front. Again, I stand to be corrected. I am here to learn about how one might go about this.

 

[Minnichds]

When you say sparky, I’m assuming you mean an electrician. You need an engineer. This is a big system, you should talk with an engineering consultant. This is a DIY forum. If you are trying to do this yourself, you need an engineer. If you are not doing any of this yourself, I wouldn’t trust anyone on a forum to have all the right safety precautions for either case. There are safety risks here that I wouldn’t trust myself doing without an engineer and I’m a journeyman.

 

[Ohms_Cousin]

When you say sparky, I’m assuming you mean an electrician. You need an engineer. This is a big system, you should talk with an engineering consultant. This is a DIY forum. If you are trying to do this yourself, you need an engineer. If you are not doing any of this yourself, I wouldn’t trust anyone on a forum to have all the right safety precautions for either case. There are safety risks here that I wouldn’t trust myself doing without an engineer and I’m a journeyman.

Well sure. I get your point. However I have been reading this forum since inception and there are some pretty clever ppl here. I know the ones who's opinion I would trust and hope they chime in on the thread. In the end it would all have to be run by my sparky. He is a clever guy as well and no fool. But he doesn't have time to sit around brain storming possible ways of doing things. In fact its hard to get hold of him because he is so busy and in such demand.

 

[SamDeleted]

You are getting into the tens of thousands here likely. You are not an electrician or an engineer? Do you really trust yourself with an install in that range with all of the proper safety precautions taken?

Especially at sea , marine electrics have to be taken seriously

 

[Minnichds]

You could throw solar up front with an inverter charger. You could run DC or AC. Neither one should be more cost effective than the other and can both be done right.

DC is the easiest for install and labor, but you are talking some of the biggest wires in the industry, and the most expensive safety devices. AC would make the cables running the length to be considerably smaller. But then you need a system to convert back to DC to charge. This puts you in the tens of thousands.

Like honestly, no one on here is going to give you a good recommendation without seeing anything you are asking about.

All of the safety devices for this make neither one of these scenarios to be preferential.

If you have to have ac up front, go that route now. It’s going to be expensive but ultimately look the best. If you know you will not need AC up front, stick to AC because while DC is electrically safer, cables that big require some very specialized equipment and you get into a very high Amp range which still has potential for arc blast, arc fault, and damaging equipment, to the range of putting a hole in your boat and sinking it.

You could just put in an AC load center and charge that way, would be simpler to design, safer to operate and more sparky’s are familiar with these sizes of terminations. I’m not sure how much wattage you need/want up front and there are a couple ways to do this with solar and/or ac solely from the stern. A 30kW - 40kW inverter was in the 5k to 10k range. That’s about the pricing last I checked but I don’t order the ones I work on. I’d find an inverter charger or inverter charger Mppt. These will have shore power input for redundancy. Marine grade everything is almost highest grade out there.

You are looking at quite a bit of money. You should really just go talk to a marine electrical consultant. If you are spending the money on this, an engineer should take all the guesswork with values and know the best.

 

[Minnichds]

None of your assumptions are correct. It just seems a strange way to barge in on a thread. I see you have 4 posts here and not been a member that long. You will find that this is a friendly place and lots of people here are happy with chatting about these types of things.

Lets just move on and think about how to move energy up and down a sail boat from stern to bow and back. DC whilst the most efficient has lots of issues attached to it. Seems like AC is the way to move that energy that far.

One thing about my setup is I need to get some weight up front to balance out all the weight going in the stern end of the boat. A big battery bank is perfect for this (another way is 200 mtrs of 10mm chain in the anchor locker, but rather get the advantage of more power onboard)

perhaps I spend too much time on electriciantalk. They like to kick everyone out.

 

[Minnichds]

I would look at the 15kW version. This would take about 4 hours to charge your bank. Unfortunately it is only 230VAC. But that may be acceptable if installed correctly, and can save you money on cabling and devices. The smaller size of the inverter may be acceptable depending on your overall power requirements you desire. But depending on what else you have aboard that may change. All cabling will need to be tinned copper marine grade, all devices need to be Marine grade. You run into grounding and bonding issues on a boat which is where a specialist will come in handy, otherwise you get galvanic corrosion in the hull.

This will not parallel with a second, however, it will do shore power and act as an UPS. This pairs really well likely with the app and all other Victron devices.

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf

 

[Tomthumb62]

You will need a big ass spool to run either AC or DC, this is in the thousands range. A crimp that size runs into the thousands. An inverter that size well in the thousands. And your batteries are also in the thousands. Do you understand how many fires I’ve seen from improperly sized and crimped equipment? If this is going out to sea this conversation might save your life. An electrician would be the only person qualified for an install like this and an engineer would be the only person qualified for an install of this. I wouldn’t recommend you perform this install if you haven’t priced out all the items to see that the capacities alone are talking pretty dangerous levels.

Running 48V would be safest for this, doing it properly is something that you make too much to do yourself. Unless you are an electrical engineer, if you are, then you are likely not on a forum asking how to do so.

Since my maths seem to be so off, I'm curious as to what size of DC cable would be required for such an install? I calculated 350 MCM for a 3% voltage drop to deliver 200A, but my voltage drop calculator tools don't work with that size cable so I extrapolated my result. A quick google search shows I can get 200 feet of 350 MCM for about $1700 (I'm sure freight would not be cheap), but that's only thousands, not tens of thousands. Just curious as to how you're coming up with a tens of thousands cost but maybe you're counting the $$$ of a marine electrical engineer to do the job?

 

[Rocketman]

Here are some pondering questions…(I am assuming Victron equipment- if otherwise substitute that brand).

Are you going to be using the front battery on a day to day basis… if so put a mppt up front and charge with solar.

Using the rear Multiplus to make 120v to run up front into the front Multiplus to charge the battery- probably could be done. But you will suffer efficiency losses. Won’t be bad when running the generator… won’t be very good when getting power from solar (there is never enough of that for sailboat). But it can be done.

As far as trying to charge with alternators (assuming a 48v alternator with external control), because of voltage drop you would want a dedicated alternator for the front battery- so the regulator can compensate for the voltage drop. That may make that part a step too expensive. Assuming you already have alternator charging on the rear battery.

I see this as a possible project, but I would get with a Victron expert engineer and make sure nonthing is overlooked. Then present it to the electrician doing the work.

 

[Ohms_Cousin]

****LONG TEXT HEAVY POST AHEAD**** fleshing out what this is all about so its better understood. I tried to keep it simple and to the point in my first post but it seems that just caused more questions then answers.

This idea struck me as a way to solve a few problems, but seems an awkward thing to do hence throwing it out there for comment. I need to get as much energy storage onboard as possible and balance out the weight distribution on the boat.

The boat is a 42ft mono. The boat needs a refit. Previous owner was a mad professor and the wiring is a mess - there are so many circuits added here and there and running everywhere that my sparky cant even follow it all. His recommendation to me was to completely remove the wiring and redo it. The boat is undergoing a refit in general, so ALL wiring is being stripped out and replaced with tinned silicone wire. I have decided to install a digital switching system since all the wiring is being removed and replaced (and the interior is out as we are rebuilding that as well) - ideal time to install digital switching.

I am keeping my diesel engine to spin the big prop. The engine has been rebuilt, injector pump and injectors have been rebuilt as well. However I am installing 2 x 6kW electric pods - one starboard and one port. The pod boxes have been fabricated and joined to the hull already. These pods have the electric motor underwater which is great for dealing with the heat they produce. So I will have the option of diesel for long distance cruising and electric for shorter trips/needs when appropriate. I have specific needs for these pods for my particular use case, so it makes sense in my application, probably not in yours. The pods are 48v - hence the need for energy storage onboard. I am converting the galley to all electric - again, hence the need for energy onboard. I will be using either Eve 304aH cells to build out the battery banks OR will use Winston cells - not decided yet. Winston are undeniably better sturdier cells given the way they are built but I can get almost twice the capacity for the same cost using the Eve cells.

I will be using a High Output alternator at 48v and use a wakespeed 500 with either a REC BMS or a Batrium BMS. I like the way Batrium allows for batteries at different locations. They are both expensive BMS's so both will be fit for purpose given the engineering in them. I will be installing a 56v DC genset in the back hatch - i had another thread here running about that. I will be building a new awning over the cockpit for both shade and a place to mount new generation solar panels. The boat had 4 solar panels with it but I am sure they were issued to Noah when he built the ark all those years ago. Lots of improvements to latest solar panels - most are now 21 to 22% efficient. Given I need to get the solar power into a 48v battery the panels will have to be wired in series which is not ideal on a sail boat, but it is what it is.

So with that back ground I have two problems to work out. I am adding a lot of weight to the stern area of the boat. I need to balance out the boat with weight up front. I could take the easy route and simply add more chain in the anchor locker as that weight adds up real fast and its never a bad thing to have extra chain for anchoring up in a deep spot (5:1 is ideal). So could go that way and problem solved.

However I would prefer to get another 30-45kWh of energy onboard and I have a spot up front that would work for this. And THAT is what my current dilemma is all about (excuse the pun).

I will be installing Victron Inverter/chargers and all associated Victron control gear. There will be a 45 kWh battery bank in the stern area, so close to charge sources and the inverter DC input. So thats relatively easy. However if I want to put another 30 or 45 kWh of battery up front it becomes problematic. Its simply not feasible to run DC cables from the stern to the bow area. It is doable but not practical. So how to do this ?

It occurred to me that using AC to move energy from the stern to the bow is the way to go. Much simpler and easier in terms of wiring and control gear. I calculate about a 15 mtr wire run that also includes routing length. In AC this is not difficult at all.

Since I have planned to have 2 inverters onboard anyway for redundancy purposes it occurred to me that I could use one inverter in the stern area and one inverter in the bow area and move energy back forth between batteries as/if needed using AC to do it.

I am not sure of the intricacies of it but I do know it is frowned upon to power an inverters AC in from the AC out of another inverter. At least in the Victron world. So how do I do this?

Thinking it through I thought that perhaps I could use a standalone AC battery charger to do this. That is, the stern inverter powers an AC circuit that runs up to the bow area and powers a Victron AC input battery charger. In this application the distance involved is trivial for an AC circuit. Just size the AC conductor properly for the load of the AC charger with appropriate CB's etc.

The bow battery charger would charge the DC battery bank up front without issue as it is close to the batteries. All appropriate class T fuses and DC switch gear would be in place. The battery bank then powers the Bow Inverter which will be used for loads as needed. Seems to be a way to get that DC power out of the rear battery bank and move it up to the front battery bank should I need to do that. (cant move DC power from one battery bank to another battery bank unless BOTH batteries are almost exactly at the same voltage - otherwise there would be a huge current inrush from the full battery to the less charged battery).

The Bow inverter could also have AC circuits run to it so that shore power could be connected to it. If that were done then the bow inverter charger could charge up the front battery bank as normal when at the dock. The appropriate switch gear/circuits could be designed to allow all that.

The problem I have to overcome is how to charge the front battery bank when away from the dock. At dock its easy enough - use a shore power circuit up to the front inverter. But once away from the dock and only have CURRENT sources available for charging batteries - then what ? How do I move the DC current from the stern area where ALL the DC current sources are up to the front area 15 mtrs away ? Hence thinking about this AC charger idea.

I have given it a lot of thought and think it could work. The only downside I see is losses in DC from batteries to AC inverter to power an AC charger up front -> then AC to DC to charge batteries up front -> then DC to AC to power the inverter upfront. Of course there will be a number of circuits up and down the boat to be able to use that AC from the front but the wiring size is manageable at AC at the loads I am using (approx 5kW).

What I am asking here is for problems/issues I have not seen or understood in this approach. Is it doable or not? If not, why not?

My sparky is not going to sit and come up with creative solutions to my wants. I have to go to him with a basic plan of what I want. I have brain stormed this idea and think it could work but with electrical it seems there are always reasons why you cant have what you want.

 

[Tomthumb62]

I am converting the galley to all electric - again, hence the need for energy onboard.

Why all electric? Diesel or propane are extremely energy dense. Could be an issue for extremely long voyages and running out of cooking fuel but cooking with electricity takes a LOT of it. Maybe cook with fossil fuels but have a small electric cook setup should you run out of fuels. If you nix the all-electric galley, you might find you don't need as large a battery bank or maybe don't need as big of currents to run from the stern to the bow.

I see many people convert their RV's to be 100% electric. Electric hot water, cook top, oven, microwave, etc. I just don't get it. Maybe they have a desire to be completely free of fossil fuels, but currently (ha!) it doesn't make sense to me on a practical level. We have quite a small solar system in our camp trailer, which mostly just powers our fridge and a few other things besides run the minimal 12v house loads, but we use propane to cook and heat with. When it's 7 degrees F outside, we would go through 20 lbs of propane a week (not much insulation inside unfortunately), and that amount of electric heat would be insane.

As for your main problem, like was suggested before, this is a DIY forum and few here are adept in marine stuff, so hiring a marine electrical engineer sounds prudent to at least give you a working design. Working on shore is so much less complicated. If something fails, just order a new one or run to the hardware store...no such option 1800 miles out to sea.

That said, I think you're probably on the right track to run AC vs DC. There was another post here today where someone wants to generate power at their barn and send it 175 feet away to their house...it was suggested to convert it to 120v or 220v first, send it to the house and in the case of 220v, convert it down to 120v. I think you're on the right track, my guess is no one here wants to touch this because few have the marine experience.

Do keep us posted though on what you come up with, I'm curious to hear how it works out.

 

[Ohms_Cousin]

Why all electric?

Where I will be operating there is diesel available (still spotty but doable) Any GAS has to be hauled in to the boat from far far away. On a trip, if I run out of gas it becomes a headache. Plus gas shortages are common here.

I can easily generate current for charging batteries but once out of GAS then it will be eating out of cans. Overall its easier to use AC for the galley as I can charge batteries (at a cost to be sure) but cant find gas locally for all the money in China.

As well, my use case is really really niche. I am not doing any ocean crossings. Max distance away from home jetty is 700 klms (and I never lose sight of land) then back to home jetty. Planned trips would be somewhere around 14 days max before heading back home.