Anchoring Amps/Day

[JC522]

I mean “dear” in the sense that you came here apparently seeking advice, but then also paradoxically seem disposed to “know it all”, not really endearing yourself to those disposed to give knowledgeable advice. That kind of “dear”.

It’s all good.

I’m in the middle of a fiddly carpentry and plumbing project on board, and needed a humorous diversion. But I stand by my earlier book recos.

I thought it was obvious that I do know it all and I choose not to stifle myself at your expense.

And I meant "baby" in the sense that...Oh, forget it.

Wow!

 

[DriverEd]

I've been look at what it would take to justify switching to lithium batteries. So far it doesn't compute.

I measured both the RV refrigerator and the built-in refrigerator at 4.8 amps each when the compressor is running. Assuming the compressors run 50% of the time, that adds up to 115 amps/day or 80% of my electrical usage. Everything else (lights, stereo, etc) is insignificant.

At 140 amps/day I get roughly 3 days out of my 3 8D AGM batteries (405 usable amps). I usually stay at a marina and recharge every 3 or 4 days, or I can partially charge the batteries with my Honda 2200 if necessary, but that practice cuts into AGM battery life. So far, for my situation the AGM batteries are adequate and I can't justify spending ~$6000 on lithium batteries to get an additional 200 amps. I guess the argument for lithium would flip at something around 5 days at anchor. At that point, running the generator enough to keep up becomes annoying.

Look at Ampere Time LiFPO batteries, no low temperature cutout but not an issue where I am. Otherwise, class A cells and a good build, lots of tear down videos on them. I just got 4 200 AH batteries with a 100A BMS in each battery for $2,500 delivered to my door. I use about 140 AH per day with a fridge and 100L Dometic freezer. I decided to go with the lithium because they don't have the voltage drop of AGMs and can take the charge from my solar more quickly. 900 W solar array. I haven't done the install yet, but DC to DC converters are around $250, new wiring and new isolator switches. Saving almost 400 pounds.

 

[JC522]

Look at Ampere Time LiFPO batteries, no low temperature cutout but not an issue where I am. Otherwise, class A cells and a good build, lots of tear down videos on them. I just got 4 200 AH batteries with a 100A BMS in each battery for $2,500 delivered to my door. I use about 140 AH per day with a fridge and 100L Dometic freezer. I decided to go with the lithium because they don't have the voltage drop of AGMs and can take the charge from my solar more quickly. 900 W solar array. I haven't done the install yet, but DC to DC converters are around $250, new wiring and new isolator switches. Saving almost 400 pounds.

Thanks for the information. I looked up the specs and they don't list momentary max discharge current, but continuous is 250amps for their 400ah battery. Hard to tell without calling them, but I don't think it will handle the 300 amp load of a bow thruster.

 

[mckenzie.keith]

No, it doesn't if you read it literally. Anyhow, I think I was really really clear in my meaning. You don't ever get tired of this, do you????

Using amps to mean two different things is confusing. But I sense that I am not going to win you over. Maybe some day you will get tired of it and just do it the right way. But I am not going to mention this issue again in this thread.

 

[mckenzie.keith]

So, when people speak of "amps per day," they ordinarily mean is "amp hours per day."


And that's exactly what you're doing here because you're multiplying the amp draw by the hours per day. That's fine. I know what you mean. Usually it's clear when all we're talking about is the total daily load.

Or if someone says "I have a 200 Amp battery." What? Is that the max discharge or do you mean amp-hours or is that CCA or WTF? Its confusing and it makes it look like you don't know what the fuck you are talking about even if you do, and it also is more confusing for newbies who are just starting to learn about energy storage and how to calculate everything. It is much easier to do it right.

 

[JC522]

Using amps to mean two different things is confusing. But I sense that I am not going to win you over. Maybe some day you will get tired of it and just do it the right way. But I am not going to mention this issue again in this thread.

Thank you.

 

[JC522]

it makes it look like you don't know what the fuck you are talking about

I thought that should have been obvious after my very first post.

At any rate, you said that you do understand what I mean...right? Aside from omitting a /hr here and there, did I "know what the fuck" I was talking about? I guess appearances can be deceiving. Sorry if I offended when I took issue with you. It was meant to be good-natured SA banter.

I'll try to clean up my references to amps and amp/hrs and I do appreciate the corrections, mostly.

Now I have to get back to re-reading the Gida for tomorrow's meeting with the gang. Some of the guys have serious ethical dilemmas to resolve over beer and peanuts.

 

[Max Rockatansky]

My wife and I live happily at anchor/mooring full time with 760W solar, 400Ah of LFP. Draw: 150-175Ah/day; 3 Engel refrigeration units (one is a freezer); 12v water heating; 12V watermaker. (No TV.) 30N is as far north as we ever get, and have spent most of the last 5 years at around 24N, so it is warm. No auxiliary generator.

LFP are well worth it for full time liveaboard.

 

[2airishuman]

I think this thread has gone well past the point where the OP should be expected to post bare-breasted pictures of any wives and/or girlfriends he may have before receiving further advice.

 

[mckenzie.keith]

I thought that should have been obvious after my very first post.

At any rate, you said that you do understand what I mean...right? Aside from omitting a /hr here and there, did I "know what the fuck" I was talking about? I guess appearances can be deceiving. Sorry if I offended when I took issue with you. It was meant to be good-natured SA banter.

I'll try to clean up my references to amps and amp/hrs and I do appreciate the corrections, mostly.

Now I have to get back to re-reading the Gida for tomorrow's meeting with the gang. Some of the guys have serious ethical dilemmas to resolve over beer and peanuts.

You did not offend me. I interpreted it as SA banter also. I was replying to 2airishuman in that post. Wasn't meant to be aimed at you. Your calculations did seem to be sound other than the Ah vs amps. Most of the time I am able to avoid being pedantic. But sometimes I can't help it.

 

[JC522]

OK, after all that BS and thoroughly enjoyable banter (sort of) here are my conclusions:

 

[SASSAFRASS]

It's worth noting that amp hours are a useful tool and having a meter to keep track of is pretty essential, actual battery management is a bit more grey depending on batteries used and how you are charging etc. The amp hr number is dumb and as the gas gauge goes down very accurate. On the flip side not so much when you factor in charge profiles bulk absorption float and the many different batteries and charging systems. Also lots of boats use different voltages, you have to compare apples to apples, 12 24 etc

 

[toddster]

Well, the obvious common ground is watt-hours. But I find myself interpreting both the AC and DC systems in equivalent 12V amp-hours because that’s what the battery monitor is calibrated in. (Except the wind generator controller displays watts because, I suspect, the bigger numbers make you feel better about buying the thing.)

 

[Bryanjb]

I agree.
But with a generator and lithium you don't need all the solar. Lithium will do fine with a short sharp charge each day from a generator.

True enough, there are some very real advantages to lifepo4 but also some downsides. Like the sailor in Tobago last week who asked for help on the morning net because his BMS had shut down. He had no pixies to run the boat or start his engine. At the Thursday barbecue someone said it was the third occurrence he'd had in two years. That's all I know about the situation, if I hear more I'll pass on the info.

 

[mckenzie.keith]

I don't want to talk you into buying lithium batteries. The advantages are weight, lifetime and the ability to accept rapid charging. If you can live without all that, then you don't need them.
As far as life goes, you can probably shuffle 140 Ah in and out of a 200 Ah LFP battery every day for 10 years. Or you can do the same with a 200 Ah lead acid battery for, well, a few years. Will the LFP pay for itself in that time frame?

I don't think so. But it depends on how much you pay for the LFP. For example if you buy the bare cells and assemble the pack yourself, then the cost difference is much smaller. But then you get into all the questions of insurance and resale value and did you do the installation right or are you going to burn down your boat, etc.

 

[DDW]

One thing you should NOT do is install some LFP batteries with a BMS who's shut down behavior is poorly understood. There are some that reset themselves when the fault is gone, others that will not reset until charged, etc. - pretty much every variation. You want something you can and do understand, and can reset reliably at will.

 

[Zonker]

I measured both the RV refrigerator and the built-in refrigerator at 4.8 amps each when the compressor is running. Assuming the compressors run 50% of the time, that adds up to 115 amps/day or 80% of my electrical usage. Everything else (lights, stereo, etc) is insignificant.

That sounds about right (50% on time) IF compressors are air cooled and well ventilated and refrigerators are well insulated. In really hot daytime climates (35C+) the compressors will be running lots more than 50% of the time; closer to 75% but I never actually measured it; just noticed "hey the fridge is running a lot more because it's stinking hot"

If you want showers, you need a water maker. To have a watermaker, you really need to run a generator every few days to power it. I

Well no. Our first boat did not have a watermaker and we had showers every 2nd day. Just tried to swim in saltwater, wash with salt water soap, and then a final fresh water rinse. And this was in summer in the Baja where it is pretty hot. We had about 55 gallons of water and that lasted us about 3 weeks. Not exactly suffering.

On our second boat we had a 12V Spectra watermaker. Had daily showers crossing all the oceans or at anchorages. Ran off 500W of solar quite happily. We left on our 19 day passage from Mexico to the Marquesas with partly full water tanks. That is when you have confidence in your systems.

(or we were stupid but if the watermaker had died on day 2 we had enough water and juice aboard to cope; just showers wouldn't be daily).

 

[Se7en]

Well no. Our first boat did not have a watermaker and we had showers every 2nd day. Just tried to swim in saltwater, wash with salt water soap, and then a final fresh water rinse. And this was in summer in the Baja where it is pretty hot. We had about 55 gallons of water and that lasted us about 3 weeks. Not exactly suffering.

On our second boat we had a 12V Spectra watermaker. Had daily showers crossing all the oceans or at anchorages. Ran off 500W of solar quite happily. We left on our 19 day passage from Mexico to the Marquesas with partly full water tanks. That is when you have confidence in your systems.

We had almost exactly the same amount of water (220 litres) as you did, and only lasted max 10 days pottering around Queensland (so similar temps). And the kids had a shower about once a week if we beat them. We didn't want to drop our consumption below 20 litres a day - or 5 litres per day per person.

I didn't realise a Spectra watermaker was that efficient. What did it consume - 30 amps or so? We had 440 W solar and I didn't think there was a chance of being able to drive a watermaker from that.

Wow, just looked it up and they quote 10 AH for 31 litres. That's actually quite doable. Boat after next.

 

[slug zitski]

We had almost exactly the same amount of water (220 litres) as you did, and only lasted max 10 days pottering around Queensland (so similar temps). And the kids had a shower about once a week if we beat them. We didn't want to drop our consumption below 20 litres a day - or 5 litres per day per person.

I didn't realise a Spectra watermaker was that efficient. What did it consume - 30 amps or so? We had 440 W solar and I didn't think there was a chance of being able to drive a watermaker from that.

Wow, just looked it up and they quote 10 AH for 31 litres. That's actually quite doable. Boat after next.

Yah

two weeks cruise is about max for a small craft

at two weeks you run out of food , water, fuel , batteries are soft and your crew are all burnt up and begin to stink

 

[Max Rockatansky]

Ryan Finn just rounded Cape Horn with a Katadyn, and he didn’t have very much solar aboard…