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.

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[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 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 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