How Many Amp Hrs (Battery)?

[GeneraiT001]

From what I've read it is recommended to have 2 or 3 times the amount of Amps you use per day. It seems the normal amount people use is between 100 and 200 Amps/day. So is 450 amp/hr of LGA battery a good number to aim for....assuming an ocean crossing?

 

[dlochner]

More important than battery capacity is the capacity to recharge the batteries. If you use 100ah a day, you need to be able to generate 100ah a day. Having battery capacity greater than the daily use, gives a cushion for bad weather (assuming solar is the primary charging system).

Bear in mind, that charging is not 100% efficient. It will take more than 100ah to replenish the battery if you use 100ah.

How do you plan to charge the batteries?

 

[dLj]

I am not sure the statement of 100 to 200 usage per day is a good one. I feel you need to calculate what you and your boat will use per day. Usage really depends on what equipment you have on board and what lifestyle you want to have.

Personally, I set up my systems to have frugal energy consumption. I don't have a large refrigerator/freezer; I run a wind vane autopilot; all lights are LED's; most systems are mechanical. I do have an electric windlass. I also have AIS, RADAR and lots of gadgets like cell phones, computers, music. It's actually amazing how much power the gadgets use. I run Starlink but only for about two hours a day because if how much power it eats. But I haven't done the 12V conversion so I have to run the starlink and my inverter for it to run. If you are looking to get star link - look at the new mini - much better than my old system.

I have a 400 amp hour house bank of LiFePo batteries so approximately 360? Amp hours of useable battery power. I almost never let the system go that low. I will recharge at about 30 or 35% remaining battery level. My main charging sources are my solar panel and my alternators. My solar panel is about a 380 amp panel - it usually is putting out in the.mid 200 amp range, or less. I think I've seen a couple days where it was putting out a bit over 300 amps. I have twin alternators that will put out 240 amps, but I throttle them back to 80% output. I think if I had more room in my engine compartment I would put in two much higher output alternators such that I could fully recharge I say 15 minutes rather than the two hours i currently need and then drop the solar panel. But without that space, I will likely see about doubling my solar panel output.

As I'm currently set up, at anchor I am very close to self-sufficient just off my solar. But under way, I can go usually about 4 to 6 days and then I'll need to run my engine to charge.

If I was running an electric autopilot, I would likely have to charge underway almost every day.

Measure your consumption. If looking at solar, figure the real output is 50 to 60% of stated output. Calculate a way to charge your batteries in a fairly short time period if needed. Don't even consider lead acid for a house bank. You can use lead acid for start or windlass batteries, but not your house bank.

Just food for thought.

dj

 

[GeneraiT001]

Unfortunately, right now, all I have to charge with is 1x 100W solar panel and of course the engine. Seems like I need more solar. Also I do only have an electric AP Clearly not an ideal setup.

 

[colemj]

I run Starlink but only for about two hours a day because if how much power it eats. But I haven't done the 12V conversion so I have to run the starlink and my inverter for it to run. If you are looking to get star link - look at the new mini - much better than my old system.

My experience with V2, V3, and Mini Starlink is that there is little power to be saved by only going to DC. Most of the "excess" power they use is in their modems. If you use your own modem, the power usage does drop.

I'm ignoring the inverter efficiency part because that depends on the specific inverter and how it is used. If you are using a 3kW inverter just to run Starlink only, then there is power to be saved going DC. If your large inverter is on anyway for other things, then no power to be saved. If the Starlink is powered by a little 300W portable inverter, then no power is saved going DC until the SL modem is replaced with one's own.

For example, our V2 average power usage dropped from 60W to 45W going from original setup running off a 300W inverter to using a DC POE converter and our boat router.

There is little power to be saved operating the Mini on DC because it already operates on DC. However, connecting it directly to DC is much more convenient and gets rid of the inverter. Ours uses 22W on average. I have not yet bypassed its modem to determine if there is any power to be saved there, but it is a pretty small and weak modem, so don't think there will be savings - just convenience.

My solar panel is about a 380 amp panel - it usually is putting out in the.mid 200 amp range, or less. I think I've seen a couple days where it was putting out a bit over 300 amps. I have twin alternators that will put out 240 amps, but I throttle them back to 80% output. I think if I had more room in my engine compartment I would put in two much higher output alternators such that I could fully recharge I say 15 minutes rather than the two hours i currently need and then drop the solar panel.

Did you mean 20/30A solar output from your 380W panel, or 200/300Ah/day from them?

It will not be possible to recharge in 15min using larger alternators. The batteries won't (should not) take that much current, and it is unlikely 1200A of alternator output can be connected to the types of engines on most boats.

Mark

 

[colemj]

Unfortunately, right now, all I have to charge with is 1x 100W solar panel and of course the engine. Seems like I need more solar. Also I do only have an electric AP Clearly not an ideal setup.

Like stated, you will need to work on the charging side of the equation. Battery capacity only gets you a single shot at power usage, then needs to be recharged. Ideally, your daily usage and charging ability should equal out.

You have more breathing room with lithium than lead batteries because lithium keeps a pretty steady voltage throughout its discharge curve, and it doesn't suffer damage from staying in a partially discharged state for long periods of time.

This means if you have a 400Ah battery, use 150Ah/day, and can replace 100Ah/day, then you can go 6-7 days without needing to add more charge than normal. This type of use will kill lead batteries, and the equipment attached to them will be unhappy with the large voltage drops. At best you might get 3 days out of this type of usage with lead.

Mark

 

[GeneraiT001]

Like stated, you will need to work on the charging side of the equation. Battery capacity only gets you a single shot at power usage, then needs to be recharged. Ideally, your daily usage and charging ability should equal out.

You have more breathing room with lithium than lead batteries because lithium keeps a pretty steady voltage throughout its discharge curve, and it doesn't suffer damage from staying in a partially discharged state for long periods of time.

This means if you have a 400Ah battery, use 150Ah/day, and can replace 100Ah/day, then you can go 6-7 days without needing to add more charge than normal. This type of use will kill lead batteries, and the equipment attached to them will be unhappy with the large voltage drops. At best you might get 3 days out of this type of usage with lead.

Mark

I've read that charging LiPo batteries is a difficult thing when charging with the alternator from the engine?

 

[dlochner]

On average solar panels can be expected to provide 3 times the nominal output per day, i.e, a 100 watt panel can be expected to provide about 300 watt-hours or 25ah. Some days will be better, some worse, summer might be a bit higher. Higher quality and more efficient panels will do a little better. My experience is consistent with this estimate.

Our Gen 3 Starlink runs on a small DC-DC converter that takes 12v and raises it to the required 54v. It draws about 4.5 amps.

OEM alternators are typically set up to output much less than their rated power to protect the alternator. Don't count that 80 amp Hitachi alternator on a Yanmar putting out 80a for very long before it drops to a much lower output.

Advances in Onboard Solar - Professional BoatBuilder: An IBEX Technical Journal

Advances in onboard marine solar technology improved efficiency and lowered the cost. But they also introduced more complexity.

www.proboat.com

Automotive Alternators vs. Deep Cycle Batteries - Marine How To

A Deep Cycle Battery Assassin The alternator pictured here helped to destroy a very expensive bank of TPPL AGM batteries in under two years. These batteries need an absorption voltage of 14.7V. The highest voltage I recorded on this vessel was 13.58V at the battery terminals. At this

marinehowto.com

 

[dlochner]

I've read that charging LiPo batteries is a difficult thing when charging with the alternator from the engine?

It is not difficult if you take the time to learn how they work and the limitations of OEM alternators. They are not drop in batteries even though advertised as such.

 

[dLj]

My experience with V2, V3, and Mini Starlink is that there is little power to be saved by only going to DC. Most of the "excess" power they use is in their modems. If you use your own modem, the power usage does drop.

Mark

I'll have to respond in a couple posts as I'm currently traveling and editing abilities are limited.

I don't have first hand knowledge on the mini vs what I have - at least not yet. But when running my setup the inverter/Starlink combo consume as much power as my refrigerator/ freezer except my refrigerator/freezer cycles on and off. So adding in starlink in my system is the equivalent of adding in a compressor running full time. It consumes 4 to 6 times or more than my refrigeration system.

From folks running the mini - their consumption is notably less. I'm going to move to the mini in the near future and then will have real numbers.

dj

 

[dLj]

Did you mean 20/30A solar output from your 380W panel, or 200/300Ah/day from them?

Mark

Yeah - sorry that's a 380 watt panel. It rarely puts out 380 watts. I typically see 200ish watt output on the peak output side. A couple times I've seen it put out in the low 300 watt range. This is not the amount of power over a 24 hour day. I can get that info from my controller, but I don't have access to it at the moment.

dj

 

[dLj]

It will not be possible to recharge in 15min using larger alternators. The batteries won't (should not) take that much current, and it is unlikely 1200A of alternator output can be connected to the types of engines on most boats.

Mark

You'll have to explain this to me. I was of the understanding lithium batteries can take whatever you can throw at them. I understand there is a limit to what an engine can deliver into the alternators for output - but it was my understanding the batteries can take whatever you can send them.

The main point is that we spend a lot of time putting all sorts of solar panels on boats and don't seem the think about putting larger alternators on our engines - with lithium I think that needs to be re-thought out.

dj

 

[dlochner]

I was of the understanding lithium batteries can take whatever you can throw at them.

I think is a popular myth and misinterpretation of the differences between a LA charge curve and a LFP charge curve. With LA batteries the internal resistance is a limiting factor, as the SOC goes up, the ability to absorb current goes down, or perhaps more correctly the voltage must go up to overcome the increasing resistance. LFP charge curves are pretty flat, the internal resistance does not increase (very much) until quite close to the end of the charge cycle, thus, it will accept what ever is thrown at it, while the LA battery will accept less.

Every battery has an acceptable charge rate. This is determined by the battery construction and the BMS. For example, if the C rating is 1, then the battery can safely accept a charge current equal to capacity, a 100 ah batter can accept 100a at 1C, a 100 amp battery with a .5C charge capacity can accept a 50a charge, and so on. In another long thread on SBO there were several articles cited on the safety of LFP batteries and thermal runaway. A key factor was the charge rate and ambient temperature. At charge rates above 1C and in a warm environment the risk of thermal runaway was significantly higher than at lower charge rates.

 

[colemj]

You'll have to explain this to me. I was of the understanding lithium batteries can take whatever you can throw at them. I understand there is a limit to what an engine can deliver into the alternators for output - but it was my understanding the batteries can take whatever you can send them.

The main point is that we spend a lot of time putting all sorts of solar panels on boats and don't seem the think about putting larger alternators on our engines - with lithium I think that needs to be re-thought out.

dj

@dlochner explained it. I don't know of any LFP cell manufacturer that specs a safe charging current higher than 1C, and very, very few drop-ins that allow even 1C. Then there is the BMS between the charging source and battery, where no mosfet based BMS is going to allow that charge rate. Contactor based ones don't care, but you will exceed the safe charging spec of the manufacturer.

Then there is the fusing and cabling nightmare. Safely getting 1200A of current to a 400Ah battery would be tricky and expensive.

We have 3kW of solar and 275A and 115A externally regulated alternators, so some of us think about both .

Mark

 

[colemj]

I don't have first hand knowledge on the mini vs what I have - at least not yet. But when running my setup the inverter/Starlink combo consume as much power as my refrigerator/ freezer except my refrigerator/freezer cycles on and off. So adding in starlink in my system is the equivalent of adding in a compressor running full time. It consumes 4 to 6 times or more than my refrigeration system.

From folks running the mini - their consumption is notably less. I'm going to move to the mini in the near future and then will have real numbers.

dj

Yeah, that took us by surprise also. Shouldn't have, but we just didn't think about it in that way when we got it.

The mini is considerably less power hungry. 22W average and 43W peak when heavily loaded at maximum output. This is half the V2 dish power use. We are in the process of deciding whether to use that or our V3 as our primary dish (the V3 uses even more than the V2). The downside of the mini is throughput speed and ability to stay connected in rain and in extreme motion. But these are generally within acceptable ranges for most people. If you do heavy work through your Starlink, the mini might not cut it.

Mark

 

[dLj]

I think is a popular myth and misinterpretation of the differences between a LA charge curve and a LFP charge curve. With LA batteries the internal resistance is a limiting factor, as the SOC goes up, the ability to absorb current goes down, or perhaps more correctly the voltage must go up to overcome the increasing resistance. LFP charge curves are pretty flat, the internal resistance does not increase (very much) until quite close to the end of the charge cycle, thus, it will accept what ever is thrown at it, while the LA battery will accept less.

Ah - yeah, that is so far beyond what normally is available for charging - that I can see why I never bothered worrying about it.

I'm charging at about 0.5 C - pretty sure my batteries will accept 1C but I will check although I've no plans to change any of that part of the system at this point. 2 hours of engine use, completely low batteries and I'm fully recharged. Pretty happy with that setup.

We are always talking about adding more and more solar. I do think with lithium batteries we should begin looking more at our alternators and establishing a better understanding of that side. If I could move to double my current solar - I would be pretty much completely energy independent, even on long passages with my full bridge running.

Now heat and AC? Well, heat I'll move to diesel. I don't know yet what to do about AC... I currently run a heat pump that does both but it's pretty limited. I never use it on passage. If one wants either or both of those to run off solar - that's a big ask!

dj

 

[colemj]

Ah - yeah, that is so far beyond what normally is available for charging - that I can see why I never bothered worrying about it.

I'm charging at about 0.5 C - pretty sure my batteries will accept 1C but I will check although I've no plans to change any of that part of the system at this point. 2 hours of engine use, completely low batteries and I'm fully recharged. Pretty happy with that setup.

We are always talking about adding more and more solar. I do think with lithium batteries we should begin looking more at our alternators and establishing a better understanding of that side. If I could move to double my current solar - I would be pretty much completely energy independent, even on long passages with my full bridge running.

Now heat and AC? Well, heat I'll move to diesel. I don't know yet what to do about AC... I currently run a heat pump that does both but it's pretty limited. I never use it on passage. If one wants either or both of those to run off solar - that's a big ask!

dj

Pretty much all batteries will happily take 0.5C charge rates. While it is good to be able to fully charge them fast, in practice all that is needed is to inject the day's use of charge into them. They are happy to stay partially charged forever.

Solar is kind of an easy thing - you add what can reasonably fit, and that is that. Then decide how much surplus/shortfall in energy you have and work on those alternatives.

If you haven't bought solar in the past several years, you might be surprised at the efficiency gains made there. You might be able to increase your capacity 50-100% just by replacing your existing panel with a new one.

We run A/C off our batteries for 10hrs every night. A few hours on the main unit cooling during cooking time, and 8hrs on the bedroom unit for sleeping. To do this, we have variable speed/capacity units that are energy efficient. The power usage is reasonable - ours uses 100-120Ah/night, which is 10-12% of our battery capacity. Using the more common old style units still sold for boats is not as easily accomplished, as they are very power hungry.

If we want A/C on passage, and the solar isn't producing as much because of weather or shadows, it is a matter of 30min on the engine alternator to replace the power used by the A/C every day.

Mark

 

[dLj]

Pretty much all batteries will happily take 0.5C charge rates. While it is good to be able to fully charge them fast, in practice all that is needed is to inject the day's use of charge into them. They are happy to stay partially charged forever.

Solar is kind of an easy thing - you add what can reasonably fit, and that is that. Then decide how much surplus/shortfall in energy you have and work on those alternatives.

If you haven't bought solar in the past several years, you might be surprised at the efficiency gains made there. You might be able to increase your capacity 50-100% just by replacing your existing panel with a new one.

We run A/C off our batteries for 10hrs every night. A few hours on the main unit cooling during cooking time, and 8hrs on the bedroom unit for sleeping. To do this, we have variable speed/capacity units that are energy efficient. The power usage is reasonable - ours uses 100-120Ah/night, which is 10-12% of our battery capacity. Using the more common old style units still sold for boats is not as easily accomplished, as they are very power hungry.

If we want A/C on passage, and the solar isn't producing as much because of weather or shadows, it is a matter of 30min on the engine alternator to replace the power used by the A/C every day.

Mark

I think this is a great discussion showing two different views of cruising.

I try to run my engine as little as possible. I feel it better to have an energy usage that keeps my engine off. But when I do have to run my engine, I want the charging needs to be as short of a time as I can get away with. This minimizes engine hours and maintenance costs.

It also allows me to travel quite far and use the times I would normally run my engine to top up my batteries. Coming into ports or going out of ports I'll likely be motoring. During those times my batteries are getting fully charged. My normal power usage both at anchor and underway are such that I go quite a bit of time without needing to run my engine. At anchor, I'm almost totally self-sufficient, under way with all my bridge running, I'm going about a week. But I don't need AC. If I did - I'd need to reconfigure to still have that autonomy.

dj

 

[BAD ORCA]

I think this is a great discussion showing two different views of cruising.

I try to run my engine as little as possible. I feel it better to have an energy usage that keeps my engine off. But when I do have to run my engine, I want the charging needs to be as short of a time as I can get away with. This minimizes engine hours and maintenance costs.

It also allows me to travel quite far and use the times I would normally run my engine to top up my batteries. Coming into ports or going out of ports I'll likely be motoring. During those times my batteries are getting fully charged. My normal power usage both at anchor and underway are such that I go quite a bit of time without needing to run my engine. At anchor, I'm almost totally self-sufficient, under way with all my bridge running, I'm going about a week. But I don't need AC. If I did - I'd need to reconfigure to still have that autonomy.

dj

I completely agree but...Nigel Calder warns, and Colemj briefly eluded to, that there is a limit to the size of an alternator that can be put on any engine before it starts to significantly rob the engine of horse power, and then becomes a liability with the ability to permanently and prematurely damaging the engine.

Most cruisers parallel multiple lithium batteries in a single bank, so the C-rate really becomes a non-issue. Even with multiple budget batteries. The limiting factor then becomes the amount of solar, other methods of energy generation, and the maximum size alternator that can safely be put on a particular engine without mechanically damaging it. I think it was in one of the recent 'boat how to' videos on youtube he (Nigel Calder) touched on alternator sizing.

 

[colemj]

I think this is a great discussion showing two different views of cruising.

Sounds like similar views to me - balance energy usage with power generation, with an eye toward minimizing ICE time. We also want to keep engine running time to a minimum, which is why we have a lot of solar and large alternators. The solar allows us to keep our engine off and meet our energy usage. When we do need to run the engines, they can supply 300A of charging, which minimizes the time they are needed on. Generally, the solar more than supplies our electrical needs at anchor, with the engine only needed after several days of rain.

We also have several options that can conserve power. We run our watermaker, water heater, convection oven and induction plate, and A/C off the batteries. Forgoing any or all of those for a day or two doubles our reserve time on batteries, or can even keep us total full with solar during cloudy and rainy days.

Mark