Real world electrical consumption?

[SY Kelpie]

Part of my thinking about water-cooled refrigeration is that it dumps the heat outside of the boat. I've never lived in a warm climate and overheating is one of the things that concerns me about cruising the tropics.

One other thought- I'm toying with a hybrid Lithium/Lead system. Basically I can't afford to have the whole boat running on Lithium, much as I would like to, and I get a little nervous about destroying an expensive lithium battery bank through stupidity/error/malfunction. Then there's the intricacies of putting a big bank made of multiple batteries.

However, if I can get my average at-anchor usage down to the 100Ah region, I could fit a single LiFePO4 battery big enough to handle that. It would be relatively affordable, and easier to fit. It would also recharge quickly and efficiently, and not be damaged by failing to reach full charge.
Something like this: https://shop.gwl.eu/LiFeYPO4-batteri...LP12V90AH.html although ideally a bit bigger, maybe 120Ah nominal.

Complementing this would be a conventional lead-acid bank used mostly as a reserve, which I could dip in to when on passage or on cloudy days. This would probably be the engine start bank as well. It would get priority for charging to make sure it remains at 100% as much as possible, extending its lifespan.

[teneicm]

Originally Posted by SY Kelpie

Part of my thinking about water-cooled refrigeration is that it dumps the heat outside of the boat. I've never lived in a warm climate and overheating is one of the things that concerns me about cruising the tropics..

Ive read that the amount of heat generated by the average refrigeration system is equivalent to the heat give off by a person. So really not that much to worry about as far as heating up the boat. If you want to keep the heat off the boat, go the keel cooler route. Anything other than piping raw water through coils. Seems.like a good idea at first, but after removing your 32nd dead sea creature from the lines, or having to run acid thought the coils to remove growth and calcium buildup, or any of the myriad of other issues inherent with raw water cooling, you'll change your mind. I did.

[mvweebles]

Originally Posted by teneicm

The coils don't go in the tank. You just T a line off the tank supply as well as the return. The water just circulates from the tank, to the compressor/ coil unit, and back to the tank. We converted our water cooled system to this arrangement and it is working great. 80 gallon water tank, cooling a 7 cubic foot freezer. Works fine as long as we keep the tank above 1/4 full. Will work with as little as 5 gallons, but it starts to lose efficiency at that point. The tank is usually around 90 degrees, which is only 2-3 degrees above the sea water temp. It will work even better out of the tropics. Air cooled is very reliable, but we had issue with where the unit could be installed, but still get good air flow. The water cooled unit can be stuck in a much smaller, less ventilated space (although you still need some fresh air, you don't want the compressor and black box overheating!)

Thanks for the explanation. Makes sense. Thinking about it, a fridge compressor only pulls about 35 ah per day so a decent sized water tank should be fine as you say. Next time I'll do that - easy, quiet, and efficient. Only down side is a small pump is needed to circulate the water. Not a big deal.

I learn something everyday, often from this forum!

Peter

[mvweebles]

Originally Posted by SY Kelpie

Part of my thinking about water-cooled refrigeration is that it dumps the heat outside of the boat. I've never lived in a warm climate and overheating is one of the things that concerns me about cruising the tropics.

One other thought- I'm toying with a hybrid Lithium/Lead system. Basically I can't afford to have the whole boat running on Lithium, much as I would like to, and I get a little nervous about destroying an expensive lithium battery bank through stupidity/error/malfunction. Then there's the intricacies of putting a big bank made of multiple batteries.

However, if I can get my average at-anchor usage down to the 100Ah region, I could fit a single LiFePO4 battery big enough to handle that. It would be relatively affordable, and easier to fit. It would also recharge quickly and efficiently, and not be damaged by failing to reach full charge.
Something like this: https://shop.gwl.eu/LiFeYPO4-batteri...LP12V90AH.html although ideally a bit bigger, maybe 120Ah nominal.

Complementing this would be a conventional lead-acid bank used mostly as a reserve, which I could dip in to when on passage or on cloudy days. This would probably be the engine start bank as well. It would get priority for charging to make sure it remains at 100% as much as possible, extending its lifespan.

Lead acid charges at different voltage than lithium so you will need to keep them separate. I went with lithium for house bank (700ah) and AGM for start and thruster batteries. I use a DC-DC charger to charge the AGMs from the house bank when there is excess power which could come from solar, alternator, or shore power.

100ah house battery, even if LFP, sounds a bit light for 100ah budget. You may want to plan for expansion and install with larger cables where needed and similar.

Good luck

Peter

[SY Kelpie]

Originally Posted by mvweebles

Lead acid charges at different voltage than lithium so you will need to keep them separate. I went with lithium for house bank (700ah) and AGM for start and thruster batteries. I use a DC-DC charger to charge the AGMs from the house bank when there is excess power which could come from solar, alternator, or shore power.

100ah house battery, even if LFP, sounds a bit light for 100ah budget. You may want to plan for expansion and install with larger cables where needed and similar.

Good luck

Peter

Yes they would be two separate banks.
Charging prioritises the lead-acid bank, and when that is full the Li bank gets charged.
The Li bank gets used first, and when it reaches voltage cut-off we switch to the lead-acid bank.
I would probably want some sort of low voltage alarm on the lead-acid bank as well, so that there was enough left to start the engine.

I haven't looked into this in a lot of detail yet. I'm hoping that my solar charge controller can be clever enough to handle the two different types of battery, and that I can set it to prioritise the lead-acid bank. Presumably I will need a VSR to switch banks when the Li bank gets down to 10% or so.
I don't know if I would need a BMS for a single 12v battery?
I'm not sure about engine charging either. I know that I want to avoid B2B using the lead-acid bank to charge the Li bank, as that would be very inefficient. B2B should be OK the other way round, I think, but that only works if I charge the Li bank first.

As you say 100Ah is light, most days we would totally drain it. I can get 2x60Ah batteries instead, the cost per Ah is about the same, but I'm still learning about all of this and intuitively assume that the simplicity of a single battery would be easier to manage. Maybe it makes no difference so long as they are in parallel?

[AKA-None]

Just remember that if you have a generator you will need to actually use it periodically. Unused stuff tends to fail if not used. Particularly generators tend to run but not generate power, one of their failure modes.

[mvweebles]

Originally Posted by SY Kelpie

Yes they would be two separate banks.
Charging prioritises the lead-acid bank, and when that is full the Li bank gets charged.
The Li bank gets used first, and when it reaches voltage cut-off we switch to the lead-acid bank.
I would probably want some sort of low voltage alarm on the lead-acid bank as well, so that there was enough left to start the engine.

I haven't looked into this in a lot of detail yet. I'm hoping that my solar charge controller can be clever enough to handle the two different types of battery, and that I can set it to prioritise the lead-acid bank. Presumably I will need a VSR to switch banks when the Li bank gets down to 10% or so.
I don't know if I would need a BMS for a single 12v battery?
I'm not sure about engine charging either. I know that I want to avoid B2B using the lead-acid bank to charge the Li bank, as that would be very inefficient. B2B should be OK the other way round, I think, but that only works if I charge the Li bank first.

As you say 100Ah is light, most days we would totally drain it. I can get 2x60Ah batteries instead, the cost per Ah is about the same, but I'm still learning about all of this and intuitively assume that the simplicity of a single battery would be easier to manage. Maybe it makes no difference so long as they are in parallel?

Get Battle Born LFP batteries. They come with an onboard BMS. My understanding is it would be a mistake to expect the two different battery types to play nice together. DC-DC chargers are not that expensive - $100 or so. And they are not that large.

Multiple batteries are not complicated. Attached is a schematic for best-practice - use a pair of bus bars (one for + and one for -) instead of simple cables to create the bank.

[SY Kelpie]

Battle Born are twice the price of the one I was looking at, which kind of kills the whole concept for me from a budget point of view I'm afraid.

Apologies for all the newbie questions... do you always need a BMS? Even if it's just one battery?

As for the two different types of battery playing nicely together... yes I can see why this would be a concern since they want different charging regimes etc. But it wouldn't be my intention to ever bridge them and run the banks together in parallel. We would be running off one bank, or the other, ideally using a VSR switching system. Anything that can't handle a momentary interruption of power, such as instruments, might be best run off the lead-acid bank anyway, leaving the Li primarily for the fridge, laptop charger, cabin lights etc.

The biggest hurdle I can see just now is getting a solar charge controller to recognise the two different battery types and charge them accordingly, whilst prioritising the lead-acid bank. It would be easier to charge the Li bank first and then use B2B to charge the lead-acid. But that leaves the risk of not fully recharging the lead-acid bank, which eventually damages it, whilst the Li bank won't mind whether it gets back to full charge or not. If I go B2B the other way around I think I will get much poorer efficiency. Maybe I will need two different charge controllers, which could add a lot of cost.

[mvweebles]

Originally Posted by SY Kelpie

Battle Born are twice the price of the one I was looking at, which kind of kills the whole concept for me from a budget point of view I'm afraid.

Apologies for all the newbie questions... do you always need a BMS? Even if it's just one battery?

As for the two different types of battery playing nicely together... yes I can see why this would be a concern since they want different charging regimes etc. But it wouldn't be my intention to ever bridge them and run the banks together in parallel. We would be running off one bank, or the other, ideally using a VSR switching system. Anything that can't handle a momentary interruption of power, such as instruments, might be best run off the lead-acid bank anyway, leaving the Li primarily for the fridge, laptop charger, cabin lights etc.

The biggest hurdle I can see just now is getting a solar charge controller to recognise the two different battery types and charge them accordingly, whilst prioritising the lead-acid bank. It would be easier to charge the Li bank first and then use B2B to charge the lead-acid. But that leaves the risk of not fully recharging the lead-acid bank, which eventually damages it, whilst the Li bank won't mind whether it gets back to full charge or not. If I go B2B the other way around I think I will get much poorer efficiency. Maybe I will need two different charge controllers, which could add a lot of cost.

To my knowledge, your solar controller won't automatically detect the battery type.

Most people use a DC to DC charger to compensate for disparities in charging.

Batteries in the 100ah range I looked at have on board BMS. But they are in the $900 range. If you want to build your own system with cells and BMS, go for it. Disregard everything I've said as I know nothing about DIY LFP systems.

[mvweebles]

Battle born are $950 for 100ah.of you are finding LFP batteries at under $500 for 100ah, it's a fantastic deal. AGMs are in the $350 range.

[SY Kelpie]

Originally Posted by mvweebles

To my knowledge, your solar controller won't automatically detect the battery type.

Yes I think asking it to know automatically would be a stretch too far! But I'm hoping that a controller can be found that you can pre-program different parameters for each bank. I'm sure it's all there in the manufacturers' blurb if I can get my head around it.

Most people use a DC to DC charger to compensate for disparities in charging.

Batteries in the 100ah range I looked at have on board BMS. But they are in the $900 range. If you want to build your own system with cells and BMS, go for it. Disregard everything I've said as I know nothing about DIY LFP systems.

Battle born are $950 for 100ah.of you are finding LFP batteries at under $500 for 100ah, it's a fantastic deal. AGMs are in the $350 range.

All there in the link I posted (https://shop.gwl.eu/LiFeYPO4-batteri...0AH.html?cur=0) which is 90Ah for $448. Not something you have to build from individual cells, but neither does it have inbuilt BMS. The supplier seems to have a good reputation.
I've seen even cheaper deals e.g. on eBay or Alibaba, which for a similar or lower price claim to have a BMS. But I'm a bit more wary of those as the adverts are written in Chinglish and I'd be concerned about what would happen if I ran in to trouble.