How Many Amp Hrs (Battery)?

[colemj]

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.

There is that, but there is also the impracticality in terms of wiring and fuses and switches of delivering that power. 4/0 wire is rated to ~400A.

If one wanted to go with really large alternators, one would need to move into higher voltages to even be practical. 48V is probably the minimum.

C-rate is a non-issue for most people simply because few can provide that much charging capacity. It would only come into play with a large charger on a small battery, which isn't a normal installation. But we touched on the question of using >1C charge rates, and that is why it was discussed.

Mark

 

[dLj]

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....

Mark

I was referring more to the difference in a mono hull vs a cat.

You have 1000 amp hours of batteries (I think), I have 400. Not sure what you've got for solar generation, but a while lot more than I have, and it would be quite a chore for me to double what I've got - probably not a concern for you. Yes, I have a fairly modern panel - upgrading will be difficult.

Look at the list of equipment you have mentioned that I have not - water heater (I have one but unless I'm on shore power I only use engine generated hot water), induction stove and convection oven (I use propane), water maker (this may come, but as i carry 220 gallons of fresh water, not in the immediate future).

I'm not trying to compare monos with cats, but the two are very different when it comes to setting them up for long term living. While I agree we are both looking to minimize ICE use - we are coming at it from two rather distinct angles.

dj

 

[dlochner]

I suspect by now we have lost @GeneraiT001, the OP. To get back to his question...

There are 2 sides to the equation, charging and usage. The goal is to charge capacity and usage be equal.

To determine battery needs:

1. Estimate daily consumption when sailing and at anchor.
2. Decide on the number of days of electrical power is needed assuming no charging, or how long can the battery bank go without charging?

The answers to those questions will determine battery size. For instance, if electrical consumption is 120ah per day while sailing and the interval between charging is 3 days, the battery bank will need to be 3 * 120 =360 ah of usable battery capacity. With lead acid that means about 720 ah and for LFP about 400 ah. At anchor, the draw will be less, so the charge interval can be longer.

Charging capacity:

In this example, every three days it is necessary to return 360ah plus 15% for efficiency costs to the batteries. Using Calder's estimate of daily solar output to be 3 times the panel's nominal output the panel size can be estimated. First change the amphours to watt-hours by multiplying ah by voltage, the 360ah is equal to 4,320 wh. Divide by 3 to get panel size. For this example the panel size would need to be about 1,500 watts.

It works about the same with determining alternator size. A safe charge rate for LFP batteries will be around .5C, which would require a 200 amp alternator capable of producing 200 amps for about 2 hours of engine run time. Unless the engine room is exceptionally well ventilated to keep the alternator cool, a more realistic estimate of output would be closer to 100 amps.

Once you get your head wrapped around these basic hypothetical issues, you can begin to bring the numbers in to real life situations. Dealing with the limitations of the boat, your wallet, and what actually happens with sailing.

When are you planning to leave on your journey to the Azores and Israel?

 

[GeneraiT001]

Wrt to LiPo batteries...is there any advantage/disadvantage to getting one large LiPo (like 450AmpHr) or 4 smaller ones (4x100 AmpHr) aside from the extra cabling? Does each LiPo need an independent BMS?

 

[GeneraiT001]

I suspect by now we have lost @GeneraiT001, the OP. To get back to his question...

There are 2 sides to the equation, charging and usage. The goal is to charge capacity and usage be equal.

To determine battery needs:

1. Estimate daily consumption when sailing and at anchor.
2. Decide on the number of days of electrical power is needed assuming no charging, or how long can the battery bank go without charging?

The answers to those questions will determine battery size. For instance, if electrical consumption is 120ah per day while sailing and the interval between charging is 3 days, the battery bank will need to be 3 * 120 =360 ah of usable battery capacity. With lead acid that means about 720 ah and for LFP about 400 ah. At anchor, the draw will be less, so the charge interval can be longer.

Charging capacity:

In this example, every three days it is necessary to return 360ah plus 15% for efficiency costs to the batteries. Using Calder's estimate of daily solar output to be 3 times the panel's nominal output the panel size can be estimated. First change the amphours to watt-hours by multiplying ah by voltage, the 360ah is equal to 4,320 wh. Divide by 3 to get panel size. For this example the panel size would need to be about 1,500 watts.

It works about the same with determining alternator size. A safe charge rate for LFP batteries will be around .5C, which would require a 200 amp alternator capable of producing 200 amps for about 2 hours of engine run time. Unless the engine room is exceptionally well ventilated to keep the alternator cool, a more realistic estimate of output would be closer to 100 amps.

Once you get your head wrapped around these basic hypothetical issues, you can begin to bring the numbers in to real life situations. Dealing with the limitations of the boat, your wallet, and what actually happens with sailing.

When are you planning to leave on your journey to the Azores and Israel?

Hi...Haven't left , reading all the replies

I could never see getting 1500W of solar!! Maybe 300-400 at most. I guess I will be running the engine a lot more

Not planning to go to the Azores/Israel til late next year. I plan on upgrading the boat so that it will be passage ready . Still need to paint the hull. I only take possession of the boat at the end of this month. Of course, winter is not far off so won't be able to do much til the spring (except save up some money...hopefully). Still gotta figure out how to sail as well

 

[dlochner]

Wrt to LiPo batteries...is there any advantage/disadvantage to getting one large LiPo (like 450AmpHr) or 4 smaller ones (4x100 AmpHr) aside from the extra cabling? Does each LiPo need an independent BMS?

Redundancy. If 1 of 4 batteries fail, then there are 3 more. The vast majority of batteries have a built-in BMS. Communication between the BMSs is another issue.

 

[GeneraiT001]

Redundancy. If 1 of 4 batteries fail, then there are 3 more. The vast majority of batteries have a built-in BMS. Communication between the BMSs is another issue.

So definitely get more than one? Is there any issues with connecting them in parallel....does each one need a separate charger?

 

[dlochner]

So definitely get more than one? Is there any issues with connecting them in parallel....does each one need a separate charger?

Yes they can be put in parallel, some batteries have a limit on the number of batteries that can be put in parallel, mine have a 4 battery limit.

Let me be frank, you're planning a really challenging and serious adventure with an Atlantic Crossing and there is a lot you need to learn to do it safely. While asking questions on Internet forums can be informative, it is a tough way to learn quickly and relatively painlessly. This thread is a good example, the information Dave, Mark, and I have provided is accurate, however, much of the conversation has not been about basics, it pretty much assumes the reader knows about electric circuits and boat systems. As a retired educator, I think you would be well served by a more formal and organized introduction to the many topics you will need to learn about, from sanitation to electrical systems. An excellent resource for the electrical systems and diesel mechanics is BoatHowTo.com It is run by Nigel Calder and one other person. Nigel knows how to teach and knows his stuff. Check it out.

 

[GeneraiT001]

Yes they can be put in parallel, some batteries have a limit on the number of batteries that can be put in parallel, mine have a 4 battery limit.

Let me be frank, you're planning a really challenging and serious adventure with an Atlantic Crossing and there is a lot you need to learn to do it safely. While asking questions on Internet forums can be informative, it is a tough way to learn quickly and relatively painlessly. This thread is a good example, the information Dave, Mark, and I have provided is accurate, however, much of the conversation has not been about basics, it pretty much assumes the reader knows about electric circuits and boat systems. As a retired educator, I think you would be well served by a more formal and organized introduction to the many topics you will need to learn about, from sanitation to electrical systems. An excellent resource for the electrical systems and diesel mechanics is BoatHowTo.com It is run by Nigel Calder and one other person. Nigel knows how to teach and knows his stuff. Check it out.

Hi,
Believe when I say I won't be venturing forth without the knowledge and confidence needed. I was a military pilot for 35 yrs and find there is a pretty good similarity wrt the basic mechanics of a sailboat vs an aircraft. So not totally starting from scratch. But your point is well taken

Well definitely be checking out BoatHowTo.com

Many Thanks