Hello! I am in the process of refitting a Mirage 5.5 to turn it from basically a bare fiberglass hull into a nice camping/weekend boat for sailing on the lower Chesapeake Bay. I am learning as I go, and have reached the stage where I need to begin adding battery/charging/electrics. I have a circuit plan, but I suspect it is missing some key elements (like fuses/breakers, etc). If anyone with experience of having done this type of thing is willing to look it over (and endure my amateur diagramming), I would be greatly appreciative to get pointers and advice on how to iterate on it and make it truly workable. I think I'm on the right track, but want to make sure I don't plan out something that's going to damage my equipment due to poor design once I connect things. Thanks very much for any advice anyone can provide!
New to Wiring, Looking for Feedback on Improving Circuit Plan for a Mirage 5.5
- Thread starter JohnBisMe
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For a first timer, your drawing is quite clear and easily read. Nice job. Typically, in this drawing only the positive leads are show, it makes the drawing a little easier to read.
The use of buses is good. This helps to see the wiring neat and organized. Be sure to watch your wire gauges, the wire from the bus to battery will need to be larger than the wires on the individual circuit.
Fuses are there to protect the wire and should be placed close to the unregulated power source. A battery is unregulated power source, a solar panel is not. In a short circuit the battery can dump all of its energy in a few seconds, the instantaneous surge can be hundreds of amps. This is particularly an issue with LFP batteries, the battery requires a very specific Class T fuse because so much power can come out a LFP battery that it will arc across a blow fuse. The Class T fuses are filled with silica to prevent the arcing. The solar panels are not an unregulated source because they are limited in how much power they can produce. A 100 watt panel can not produce more than 100 watts (about 8a at 12v), so the wire can be sized to handle that current.
There is not enough charging capacity in your system. The 5 amp shore power charger will take 10 hours to recharge the batter from a 50% State of Charge (SOC) to 100% SOC. Likewise the solar is really inadequate if you are really using 6watt panels. LFP batteries have specific charging requirements, just any old battery charger won't work. Victron is a good source for smaller chargers and solar controllers. Affordable, reliable, and state of the art. A 20a charger would be the smallest one to use.
How much solar you'll need will really depend on how much energy you will consume. Start with a load analysis, identify all the devices, how much power they need, and how long they will be on. From that information you'll be able to size the panels to provide enough power.
Take the alternator from the OB out of the system. The voltage output is unregulated and may well damage the LFP battery. If this is an electric start OB, get a lawn tractor battery and wire it separately.
You're off to a good start. Take at look at MarineHowTo.com for a ton of good articles on batteries and electrical systems. High on the list is to read is the article on drop-in batteries.
The use of buses is good. This helps to see the wiring neat and organized. Be sure to watch your wire gauges, the wire from the bus to battery will need to be larger than the wires on the individual circuit.
Fuses are there to protect the wire and should be placed close to the unregulated power source. A battery is unregulated power source, a solar panel is not. In a short circuit the battery can dump all of its energy in a few seconds, the instantaneous surge can be hundreds of amps. This is particularly an issue with LFP batteries, the battery requires a very specific Class T fuse because so much power can come out a LFP battery that it will arc across a blow fuse. The Class T fuses are filled with silica to prevent the arcing. The solar panels are not an unregulated source because they are limited in how much power they can produce. A 100 watt panel can not produce more than 100 watts (about 8a at 12v), so the wire can be sized to handle that current.
There is not enough charging capacity in your system. The 5 amp shore power charger will take 10 hours to recharge the batter from a 50% State of Charge (SOC) to 100% SOC. Likewise the solar is really inadequate if you are really using 6watt panels. LFP batteries have specific charging requirements, just any old battery charger won't work. Victron is a good source for smaller chargers and solar controllers. Affordable, reliable, and state of the art. A 20a charger would be the smallest one to use.
How much solar you'll need will really depend on how much energy you will consume. Start with a load analysis, identify all the devices, how much power they need, and how long they will be on. From that information you'll be able to size the panels to provide enough power.
Take the alternator from the OB out of the system. The voltage output is unregulated and may well damage the LFP battery. If this is an electric start OB, get a lawn tractor battery and wire it separately.
You're off to a good start. Take at look at MarineHowTo.com for a ton of good articles on batteries and electrical systems. High on the list is to read is the article on drop-in batteries.
Thank you for the informative and useful reply! If you don't mind, I have a few follow-up questions based on your response?
If I am understanding correctly, I should have one of those special 'Class T' fuses between the battery and the positive Bus Bar? And also, maybe between it and the negative bus bar?
My solar panels are 2 ten watt panels. I know they won't do much besides providing some minor charging and keeping the battery topped off when sitting on the trailer in a sunny spot for a few days during a sailing vacation, but they're all that I really have room for on such a small boat. So maybe I would get more than .5 amps apiece? I was just trying to be conservative since I know sun conditions won't always provide the max energy, I assume?
My LiFePo4 battery is a 'smart' battery with a 'battery management system' and 'automatic overload protection and recovery', would either of those mitigate the problems you mentioned with using the outboard alternator? I have heard of 'voltage regulators', would something along those lines allow me to use an alternator more safely? (No need for a separate battery to start the outboard, it is a small, 5hp pull-start.
My charger, while small, is designed for Li batteries, so no worries there, but I shall look into seeing if I can manage a larger one for faster charging. My very-rough guess is that a day's sailing (including some night hours) would probably only drain about 30-40ah from the battery (I expect it to use about 2amps during the day for radio/instruments, and then maybe up to 5 at night with lights added in, but it's a very rough guess. It's a small boat with no refrigerator or microwave or radar or anything like that... just LED navigation/cabin lights, a radio, and a display for the wind and depth/speed indicators. The most power intensive item (aside from perhaps radio transmission) will be the cabin fans to use when sleeping. If I get a larger charger, would there be any danger of overloading something, or, so long as it is designed for a 12v system, I'll be good, and just enjoy faster charging times?
Finally, thank you for the note on MarineHowTo.com.... I'll peruse it and see if I can educated myself further.
Thanks very much again!
If I am understanding correctly, I should have one of those special 'Class T' fuses between the battery and the positive Bus Bar? And also, maybe between it and the negative bus bar?
My solar panels are 2 ten watt panels. I know they won't do much besides providing some minor charging and keeping the battery topped off when sitting on the trailer in a sunny spot for a few days during a sailing vacation, but they're all that I really have room for on such a small boat. So maybe I would get more than .5 amps apiece? I was just trying to be conservative since I know sun conditions won't always provide the max energy, I assume?
My LiFePo4 battery is a 'smart' battery with a 'battery management system' and 'automatic overload protection and recovery', would either of those mitigate the problems you mentioned with using the outboard alternator? I have heard of 'voltage regulators', would something along those lines allow me to use an alternator more safely? (No need for a separate battery to start the outboard, it is a small, 5hp pull-start.
My charger, while small, is designed for Li batteries, so no worries there, but I shall look into seeing if I can manage a larger one for faster charging. My very-rough guess is that a day's sailing (including some night hours) would probably only drain about 30-40ah from the battery (I expect it to use about 2amps during the day for radio/instruments, and then maybe up to 5 at night with lights added in, but it's a very rough guess. It's a small boat with no refrigerator or microwave or radar or anything like that... just LED navigation/cabin lights, a radio, and a display for the wind and depth/speed indicators. The most power intensive item (aside from perhaps radio transmission) will be the cabin fans to use when sleeping. If I get a larger charger, would there be any danger of overloading something, or, so long as it is designed for a 12v system, I'll be good, and just enjoy faster charging times?
Finally, thank you for the note on MarineHowTo.com.... I'll peruse it and see if I can educated myself further.
Thanks very much again!
Correct on the positive cable - the fuse should be on that run and within 7” of the battery post. It should be sized based on the gauge of the wire between battery and bus bar. If you’re running smaller cables from the bus bar to the loads each of those should also be fused near the bus bar based on their respective sizes. Those fuses after the bus bar can be types other than class T or can be circuit breakers, since the main class T provides the arc prevention for very high amperage. No need to fuse the negative - generally everything on the boat sits at ground potential so there’s no significant risk of overcurrent on the negative cables as long as the positives are fused.
Each 10 watt panel can reasonably be expected to provide about 3 AH per day - not a very significant amount relative to your 100 AH battery. Your energy budget of 30-40 AH per day of consumption sounds roughly plausible to me, so you’ll be running at about a 25-35 AH per day deficit; enough to keep running for weekend cruises if you conserve.
I would probably not bother connecting the outboard to the battery. The BMS is designed to protect the battery cells, but the way it does that is by disconnecting the battery from the load/charge. That means if your outboard alternator puts out too much voltage the BMS will shut everything off and you’ll have no instruments or anything else until everything gets reset. With larger alternators that could also put a voltage spike on the system large enough to damage instruments. Your small alternator might not be able to do that but it might be able to damage the alternator itself. The typical running output of the alternator probably wouldn’t amount to enough to be worth the type of regulator you’d need to use that safely.
With the 100 AH battery you should be fine with a larger 12V charger. No significant risk of damaging anything there if you went up to, say, a 20A charger. You’ll just be able to recover the energy faster, especially with the LiFePO battery that can absorb charging pretty quickly.
@Davidasailor26 advice is absolutely correct. The answer to how much solar or charging you need, is all based on the math and the math is pretty simple.
On average solar panels can be expected to produce three times the nominal rating per day, thus a 10 watt panel can be expected to produce about 30 watt hours a day. To translate that to amp hours, divide 30 by 12 (the nominal voltage), the panel will produce about 2.5 amphours a day, the 2 panels will produce 5 ah a day. Far short of your expected draw of 30ah.
To determine how much solar you would need, start with the expected ah load, 30 and multiply by 12v to translate that into watt-hours. You will need 360 wh of solar capacity to meet the demand. Now divide the 360 by 3 to determine the nominal size of the panel, 120 watts. Of course 2 60 watt panels will also work. In general smaller panels are less efficient than larger panels. The cells in the panel are connected to produce high voltages with low current, this is necessary because the wiring inside the panel is very thin. A small panel just does not have enough cells to raise the voltage high enough to trigger the controller. Many controllers will not pass current through to the batteries until the there is a 4v or 5v difference between the output voltage from the panel and the battery voltage.
There are 3 factors that determine charger size, the batteries charge acceptance rate (expressed as a percentage of capacity, for example .3C), the amount of time you wish to spend charging the battery, and budget. The data sheet for the LFP battery should list the max charge acceptance rate, often as high as .8C or 80a for 100ah battery. That would allow for the batter to be fully charged from 0% SOC to 100% SOC in about 75 minutes. A 20a charger would take about 5 hours to do the same. Budget plays a significant role, 80a chargers are really expensive, 20a chargers are only expensive. Any charger needs to have a Lithium setting or have the ability to customize the charge settings to match the batteries. Victron has some nice not too expensive chargers with Blue Tooth so the charger's output can be monitored.
Again, do not connect the OB's alternator to the LFP battery. Unless you plan on motoring for 10 or more hours a day, the charge you will get is trivial and the risk of damage to the Battery's BMS is higher. Use a small LA tractor battery to power the electric start if you need to have an electric start.
On average solar panels can be expected to produce three times the nominal rating per day, thus a 10 watt panel can be expected to produce about 30 watt hours a day. To translate that to amp hours, divide 30 by 12 (the nominal voltage), the panel will produce about 2.5 amphours a day, the 2 panels will produce 5 ah a day. Far short of your expected draw of 30ah.
To determine how much solar you would need, start with the expected ah load, 30 and multiply by 12v to translate that into watt-hours. You will need 360 wh of solar capacity to meet the demand. Now divide the 360 by 3 to determine the nominal size of the panel, 120 watts. Of course 2 60 watt panels will also work. In general smaller panels are less efficient than larger panels. The cells in the panel are connected to produce high voltages with low current, this is necessary because the wiring inside the panel is very thin. A small panel just does not have enough cells to raise the voltage high enough to trigger the controller. Many controllers will not pass current through to the batteries until the there is a 4v or 5v difference between the output voltage from the panel and the battery voltage.
There are 3 factors that determine charger size, the batteries charge acceptance rate (expressed as a percentage of capacity, for example .3C), the amount of time you wish to spend charging the battery, and budget. The data sheet for the LFP battery should list the max charge acceptance rate, often as high as .8C or 80a for 100ah battery. That would allow for the batter to be fully charged from 0% SOC to 100% SOC in about 75 minutes. A 20a charger would take about 5 hours to do the same. Budget plays a significant role, 80a chargers are really expensive, 20a chargers are only expensive. Any charger needs to have a Lithium setting or have the ability to customize the charge settings to match the batteries. Victron has some nice not too expensive chargers with Blue Tooth so the charger's output can be monitored.
Again, do not connect the OB's alternator to the LFP battery. Unless you plan on motoring for 10 or more hours a day, the charge you will get is trivial and the risk of damage to the Battery's BMS is higher. Use a small LA tractor battery to power the electric start if you need to have an electric start.
Thank you both for your advice! Based on your recommendations, I have ordered a 17amp Victron waterproof bluetooth-capable charger (I know you said 20, but the 17 fits my needs and budget and is pretty close, and should charge 3x-plus faster than what I had previously purchased. I'll forego attaching the outboard alternator, even though I'd already bought the ports and connections. That's a hard decision to take since I got the engine specifically for the alternator (which made it more expensive), but since both of you recommend against it would be foolish to fly in the face of experienced advice.
I've looked at some solar panels, and have found a flexible 55w panel that could fit on my foredeck (so long as no one wants to sunbathe there or we're not taking in the headsails). I'll figure out a way to make it removable so we can get it out of the way except when we want to charge. Together with the little panels, that would give me 75w of charging power, which based on what you've told me would get me closer to 20-25ah per day, so I'd only be running a 10-20ah/day deficit and would be good (I assume) for a weekend trip without TOO much concern about conserving.
Thanks again very much for the help!
I've looked at some solar panels, and have found a flexible 55w panel that could fit on my foredeck (so long as no one wants to sunbathe there or we're not taking in the headsails). I'll figure out a way to make it removable so we can get it out of the way except when we want to charge. Together with the little panels, that would give me 75w of charging power, which based on what you've told me would get me closer to 20-25ah per day, so I'd only be running a 10-20ah/day deficit and would be good (I assume) for a weekend trip without TOO much concern about conserving.
Thanks again very much for the help!
Your change in plans sounds good. I've found eBay to be a good place to recoup some costs from purchases that weren't needed, especially if the parts are not returnable.
Be careful with the flexible panels. Too much flexing and the tiny wires connecting the individual cells will break. The panels are really designed to be attached to a curved surface and left there. A rigid panel will be physically stronger and can be mounted on a stern rail if you have one.
Be careful with the flexible panels. Too much flexing and the tiny wires connecting the individual cells will break. The panels are really designed to be attached to a curved surface and left there. A rigid panel will be physically stronger and can be mounted on a stern rail if you have one.
I also thought the diagram was very good and easy to read. Regarding the Bilge pump I would have a switch at the panel to change from manual to automatic and also off. Maybe your going to do that but it does not show up.
It's my understanding you never want the bilge pump to be turned off. A switch from automatic to manual yes - but not one to turn it off. Don't see why you would even want that...
dj
dlj
Some of us are lake sailors and we pull our boats for the winter. My boat came from the factory this way and it has been useful. One winter I had some water collect in my bilge from a leaking anchor locker hose and it froze solid, the bilge pump ran until it deplete the batteries. I ended up having to buy not only a new bilge pump but two new batteries as well. If I'm in the water even if under aeration I do leave it in the Auto Mode. I also got it stored into an angle one year with a bit of a bow down, the auto switch was down at enough of an angle that it wold be turned on and the water couldn't get to the pump. So a couple of oddities but I was glad the factory put in a 3 way instead of just a 2 way.
I hear what you are saying, but I feel what you need is a mechanical connection you need to disconnect as part of winterization to turn that pump off, not a switch. When going through spring commissioning, you have to mechanically reconnect as part of getting ready for sailing.
There should be no way the bilge pump could be turned off by mistake while the boat is in the water...
Just my opinion.
dj
I can only say that every boat I have owned has been set up this way. It may be an ABYC requirement I'm not sure but I am glad I have had it on numerous occasions. Even if you look at the installation instructions and switches all of them I just did a quick check on have all three modes, manual, auto and off. So that is pretty compelling as well. I looked at another site and they showed about 12 switches 10 were 3 way 2 were 2 way. So it sees to be pretty biased that way. But like some one said, it's your boat you can sure do it your way.
Certainly agree with your boat your way.
I don't feel like looking up the ABYC standards, I'll leave that for others.
But as to your comment on the number of boats you've seen that have an off switch - my experience over half a century of owning and running boats I've never had a single boat set up like that. Including the one I'm currently sailing. Nor would I ever set up a bulge pump that way. If the boats in the water, that pump better be on. With no way someone can inadvertently turn it off. If I were to have a boat like that - I'd change it.
dj
As another data point - our Beneteau came from the factory with an off/auto/on switch, but with the auto part not hooked up at all, and the pump hardwired to the main battery switch. Guess it was cheaper to buy the panel with the 3 way switch in bulk than have the panel remade for the more appropriate on/off.
(And yes, they fused the hardwire close to the switch, although they put the stereo’s always-on memory wire on the same fuse. That made for some confusion and consternation when nearby lightning shorted the stereo, blowing the bilge pump fuse.)
All this to say there may be more than one acceptable way to wire that up. Make an informed decision that makes sense for how you use the boat and what risks you want to mitigate the most.
(And yes, they fused the hardwire close to the switch, although they put the stereo’s always-on memory wire on the same fuse. That made for some confusion and consternation when nearby lightning shorted the stereo, blowing the bilge pump fuse.)
All this to say there may be more than one acceptable way to wire that up. Make an informed decision that makes sense for how you use the boat and what risks you want to mitigate the most.
For what it is worth, this is a trailer sailor and won't be in the water overnight except on occassionaly weekend camping sails. I do have a bilge pump switch with on/off/auto (hence the three wires in my diagram) that I have purchased that will go just below the main switch panel. I plan to leave it on 'Auto' when sailing or away from the boat while it's in the water, 'On' for pumping out the boat when needed. Off will be for when it's out of the water, and I have a main battery switch (ALSO not shown on the diagram) to just disconnect the battery at the source when the boat is not in the water. I doubt this adds much to the bilge pump discussion, but hopefully I should be covered as far as bilge pumping is concerned?
Just when I thought this thread was done... I went to order a 'Class T' fuse to place between the battery and the rest of the electrical system, as suggested by a poster. But when I go to places like Blue Sea Systems, all their fuses are for things like '160 amps' or '320 amps' and cost $50. My little boat will draw, at maximum, less than 10 amps with absolutely everything running. Surely something more like '20 amps' would be more in my line? But the only fuses I can find in the range say things like 'For 300 Volts AC' or 'For 600 Volts AC'. Does anyone know where I can find Class T fuses that would protect my little 12v, 10amp boat system from my 100ah LiFePo4 battery? Thanks!
If the fuse is rated for more than 12V that's fine - The voltage is a maximum; as long as your system is less than the maximum voltage you don't risk having the fuse arc. It'd be better to find a fuse rated for DC voltage - DC arcs more than AC so the maximum allowable DC voltage is generally less than for AC.
As for the size of the fuse - The important thing is to fuse based on the maximum ampacity of the wires, not really based on the load. For example, if your're using 4 AWG wire with 105 degree insulation your maximum ampacity is 160 amps, so you'd fuse to that. Start by figuring the wire size you need for your loads (for example with Part 1: Choosing the Correct Wire Size for a DC Circuit - Blue Sea Systems) then fuse based on that wire size.
If the wire gauge you have is lower ampacity than the smallest Class T fuse the safest thing to do is probably to use the smallest Class T to get the arc protection in the case of a dead short, then "downstream" (further from the battery) of that add a properly sized conventional fuse.
Class T fuses and holders are expensive. Last spring there was a shortage and some people were paying over $100 for the fuse alone. That's a lot of money, but far less money than buying a new boat to replace the one burned up because of a missing fuse.
Would the ampacity be for the wires leading from the battery until the next fuse/breaker, I assume? The ampacity of the wires leading from the battery to the panel (where there are circuit breakers in the panel) is 35... so based on what I've been told here, I should get a DC-rated T fuse of 35 (or less, but more than my maximum load) amps capacity, placed close to the battery. The wires from my panel to individual loads are 20 amps, and my circuit breakers on my panel are from 15 down to 5 amps... so in both cases, the fuses/circuit breakers are less than the wire's capacity, so the fuse/breaker would go off before the wires failed, and that is what is desired, if I'm understanding it correctly? (Also, having trouble finding a fuse that fits the bill... I have been searching fuse manufacturer sites for an hour, and while 30 amp Class T fuses do exist, I can't actually find a fuse holder that fits them! Surely I can't be the only person trying to attach a LiFePo battery to a low-amperage, small boat system?)
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