New Generator or Lithium?

[Budawang]

I have a choice to make. Our 18 year old Farymann 18 W single cylinder 4 kva diesel generator has a compression problem and I can't find parts to fix it. Instead of buying an expensive new generator I'm considering biting the bullet and upgrading our batteries to 400 amp hour LiPo4s with a 2,000 watt inverter. For charging we will have a Rutland wind generator, 300 watts solar and a 100 amp alternator with its own regulator. Our existing lead acid batteries (330 amp hour house bank) are nearing the end of their life but we probably would have replaced them with AGMs if the generator was still working.

Our AC usage has included powering a microwave, electric kettle, small hot water tank, small space heater and laptops. We are part time cruisers and like living on the hook.

I understand it wouldn't be sensible to run a space heater off a lithium bank, but does the above set-up sound like a rational alternative to buying a new generator?

[Pete7]

Yes, and if once up and running you have the odd day of rain and clouds a simple little Honda genny could be on standby without breaking the bank.

Pete

[Shrew]

IMHO you're really talking about 2 different things here.

Generator: means of generating power

Battery: Means of storing power.

You really have to look at how much you're actually drawing and how much you're able to replenish over the same time period. Increasing storage capacity only stretches the potential deficit over a longer time period.

Any period of light wind, and you could still end up in the dark. Are there plans to add solar to the mix? A Honda 2K would be a means to top off batteries, but now you're really trading an onboard generator (and it's convenience) for a portable generator.

[a64pilot]

What shrew said, Lithium just avoids the long charge times and low acceptance rate of lead, but you still have to make the power to start with.
My prediction is if you do, you will be running the motor to charge more often than you think.
The 300W of solar will only give you 100AH on average, the wind? I’m not sure depends on where you are, they seem or work great in the Bahamas in Winter, but there is always wind then, I mean almost always 15 kts or so of wind.
But 100 AH isn’t much t engine with, add an inverter with the idea of actually using it, and 100AH is nothing.

[Budawang]

Originally Posted by Shrew

IMHO you're really talking about 2 different things here.

Generator: means of generating power

Battery: Means of storing power.

You really have to look at how much you're actually drawing and how much you're able to replenish over the same time period. Increasing storage capacity only stretches the potential deficit over a longer time period.

Any period of light wind, and you could still end up in the dark. Are there plans to add solar to the mix? A Honda 2K would be a means to top off batteries, but now you're really trading an onboard generator (and it's convenience) for a portable generator.

You make a good point about generation capacity being a separate issue. I would like to have more solar but space is an issue for us. I'm hoping that 300 watts solar, plus wind gen and 100 amp alternator running the engine at least 30 minutes per day (or more if we're moving around) will be enough to compensate for not having a generator. We probably average one marina night every two weeks. When we had the generator we didn't run it very much because it was unpleasantly noisy - maybe 30 minutes per day on average.

One advantage of lithium is that it's quicker to top them up so I'm hoping we won't have to run our engine for quite so long. So the type of battery storage has some relevance to power generation.

[Budawang]

Originally Posted by a64pilot

What shrew said, Lithium just avoids the long charge times and low acceptance rate of lead, but you still have to make the power to start with.
My prediction is if you do, you will be running the motor to charge more often than you think.
The 300W of solar will only give you 100AH on average, the wind? I’m not sure depends on where you are, they seem or work great in the Bahamas in Winter, but there is always wind then, I mean almost always 15 kts or so of wind.
But 100 AH isn’t much t engine with, add an inverter with the idea of actually using it, and 100AH is nothing.

Thanks for the advice. I will see if we can add a bit more solar. I think you're also implying that inverters are quite inefficient. We would only use the inverter for charging two laptops and light use of microwave and galley appliances. Won't need to run watermaker unless we are motoring. Energy use will be higher when we are sailing long distances, but we are not big energy consumers. Does the following average daily power budget for the East Coast of Australia (quite sunny and windy) look realistic?

Solar 400 watts: 120 AH
Rutland 1200 wind generator: 50 AH
Engine 30 min/day 100 amp alternator: 50 AH

Total: 220 AH.

Perhaps with this energy budget it would make more sense to have 300 AH of battery storage? It doesn't make sense having a mismatch between generation and storage capacity.

[kmacdonald]

The lithium batteries will allow high current discharge rates to power the inverter. LA batteries of the same capacity won't be able to do that.

[mlydon]

You can get 12v chargers for laptops - I bought one after cooking several regular ones with a non-sine wave inverter. And inverters are EXTREMELY inefficient for a low-draw job like that.

Matt

[a64pilot]

I wasn’t really speaking to inverter efficiency, just if your using AC appliances, it’s likely your using quite a bit of power.
Also it’s unlikely that you will get rated power from an alternator. More like half rated power.
Try to pull the whole 100 amps and it’s likely to overheat and burn out.

Personally I think running a Honda makes more sense, a Honda thru an inverter / charger will provide an honest 100 amps charging all day long. They only cost $1,000 too and are in my opinion a better option than putting hours on your high dollar Diesel just to make electricity.

Idea of lithium is of course if you use 200 AH in 24 hours, you can fully recharge in a little more than 2 hours of Honda run time, assuming you have no Solar or wind.

[Westcliffe01]

Budawang, the proposal you are laying out is a perfect recipe to be miserable with your electric system.


First of all, when planning storage for renewable energy, you should plan on being able to go 3-4 days on your storage alone. So if you need 220AH, have storage for 660AH at least. Because you can have bad weather for longer than 2-3 days and the fastest way to absolutely kill a battery of any description is to run it flat on a daily basis. Lead acid batteries run this way are likely to be dead inside a year.


Secondly, dont be connecting the little bitty alternator on your main engine to a depleted Lithium battery. Alternators on engines are designed to charge lead acid starting batteries, thats all that existed when they were designed. Lithium batteries will accept high amperage recharging, which never was the case with lead acid. So they will tend to look like a short to your alternator, that reacts in a fairly primitive fashion to the battery voltage. Dont go by the amp rating on an automotive style alternator, because thats usually a MAX rating and not a continuous rating. They are just to small and with too poor cooling to put out the kW needed to put some charge into a lithium battery in a half hour or whatever you were thinking of. You will smoke your alternator in short oder and your backup just a few minutes later...



Now, if you add a "real" alternator (like a generator) to your main motor (assuming its possible) then you do 2 things. 1) You get access to much higher kW of power electrically and it doesnt have to e at 12V it can be at whatever voltage the charge controller will accept. That might be 90V to 150V depending on the charge controller max voltage. The charge controller will internally invert the incoming voltage down to the correct voltage and amps needed based on how its been programmed for the battery. 2) you add a more significant load to the main motor so it actually loads up a bit, which is much better than simply being at a fast idle for an hour or 2 a day...


In terms of solar panels, if you buy the most efficient Mono panels you can get (Panasonic 96 cell panels are good for 22% vs typical 17-19%) and available 320W per panel. 2 of those are 640W, but you have to try to minimize shading to get the most out of them. Obviously, the more panels you have, the better but there are limits on sailboats, especially smaller ones.


In terms of batteries, there are batteries in the size you would need for fairly modest prices. https://bigbattery.com/product/24v-lifepo4-power-wall/ (they just went out of stock, will get more in I imagine) $700 each



Specs

Nominal Voltage: 24V
Nominal Capacity: 3kWh
Max Charge Voltage: 30V (each cell voltage should be less than 3.75V)
End of Discharge Voltage: 20V (each cell voltage should be more than 2V)
Maximum Continuous Charge Current: 130A @ 25℃
Maximum Continuous Discharge Current: 130A @ 25℃
Configuration: 8S
Chemistry: LiFePO4
BMS: 130A
Anderson Quick Connect: SB175


This is 125Ah at 24V, equivalent to 250Ah at 12V


3 batteries like this for $2100 + shipping would give you power for nearly 4 days, effectively 3 days since you are not going to run them flat. Charging them up will take quite a bit of juice from a generator as previously discussed because they will accept charge up to 130A each.



Good luck...

Originally Posted by Budawang

Thanks for the advice. I will see if we can add a bit more solar. I think you're also implying that inverters are quite inefficient. We would only use the inverter for charging two laptops and light use of microwave and galley appliances. Won't need to run watermaker unless we are motoring. Energy use will be higher when we are sailing long distances, but we are not big energy consumers. Does the following average daily power budget for the East Coast of Australia (quite sunny and windy) look realistic?

Solar 400 watts: 120 AH
Rutland 1200 wind generator: 50 AH
Engine 30 min/day 100 amp alternator: 50 AH

Total: 220 AH.

Perhaps with this energy budget it would make more sense to have 300 AH of battery storage? It doesn't make sense having a mismatch between generation and storage capacity.

[Adelie]

How much energy are you really using daily? Have you measured it?

How are your panels currently mounted? Do you have a Bimini?

I personally would go with a 450-600A-hr bank of FLAs. That makes running the inverter at high loads much more reasonable. It would also provide more of a cushion for low wind low sun days. If I couldn’t install a bank that big the I would look at AGMs, probably Fireflys. Getting LiFePo at this point would not mean you are an early adopter, but it’s still not terribly mature as a technology. The cost of a lithium bank is just the starting point, you need to look at you alternator regulator to or you risk frying it too.

If I was going to use electrical propulsion I would be willing to consider lithium more seriously.

When you use a generator or main engine to recharge, you want to do it first thing in the morning when batteries will accept the most current. Then let the solar and wind trickle the batteries up to full.

[Budawang]

Originally Posted by Adelie

How much energy are you really using daily? Have you measured it?

How are your panels currently mounted? Do you have a Bimini?

I personally would go with a 450-600A-hr bank of FLAs. That makes running the inverter at high loads much more reasonable. It would also provide more of a cushion for low wind low sun days. If I couldn’t install a bank that big the I would look at AGMs, probably Fireflys. Getting LiFePo at this point would not mean you are an early adopter, but it’s still not terribly mature as a technology. The cost of a lithium bank is just the starting point, you need to look at you alternator regulator to or you risk frying it too.

If I was going to use electrical propulsion I would be willing to consider lithium more seriously.

When you use a generator or main engine to recharge, you want to do it first thing in the morning when batteries will accept the most current. Then let the solar and wind trickle the batteries up to full.

We have one panel on our starboard side rail. Our yacht is a centre cockpit so no bimini. Thanks for your honest opinion about lithium. It's easy to get all starry eyed about new technology, but we are working to a budget and I want to get the most bang for my buck. I'm thinking it might be worth upgrading to a good alternator/generator as suggested by Westcliffe01. It makes sense to be able to churn out the amps and minimise engine run time. Having as much solar as practicable seems like a no-brainer as it's cheap.

Lithium batteries seem to have so many positives but, at the end of the day, it's got to make economic sense. I just read Starry Horizons blog post about their lithium installation and the cost was truly eye-watering. A lot of the cost was labour which suggests it's a very complex system.

[Pete7]

Originally Posted by Budawang

We have one panel on our starboard side rail. Our yacht is a centre cockpit so no bimini. Thanks for your honest opinion about lithium. It's easy to get all starry eyed about new technology, but we are working to a budget and I want to get the most bang for my buck. I'm thinking it might be worth upgrading to a good alternator/generator as suggested by Westcliffe01. It makes sense to be able to churn out the amps and minimise engine run time. Having as much solar as practicable seems like a no-brainer as it's cheap.

Lithium batteries seem to have so many positives but, at the end of the day, it's got to make economic sense. I just read Starry Horizons blog post about their lithium installation and the cost was truly eye-watering. A lot of the cost was labour which suggests it's a very complex system.

As you say, you could upgrade the alternator and there are lots of thread on here about that plus add more solar, indeed we just doubled ours because it's so cheap at the moment.

Then think about how you would use LifePO4 and charge it. How about a second LifePO4 bank in due course to power a mains inverter if you have regular daily mains power requirements which looks like you do. That keeps the LA batteries to power the boat 12v system. Longer term it wouldn't take much to switch to all house LifePO4 batteries if you wanted.

Certainly some interesting options, looks like you need a spreadsheet to cost the different ideas.

Pete

[Budawang]

Originally Posted by Pete7

As you say, you could upgrade the alternator and there are lots of thread on here about that plus add more solar, indeed we just doubled ours because it's so cheap at the moment.

Then think about how you would use LifePO4 and charge it. How about a second LifePO4 bank in due course to power a mains inverter if you have regular daily mains power requirements which looks like you do. That keeps the LA batteries to power the boat 12v system. Longer term it wouldn't take much to switch to all house LifePO4 batteries if you wanted.

Certainly some interesting options, looks like you need a spreadsheet to cost the different ideas.

Pete

Thanks Pete. We need to replace our lead acids as they're on their way out anyway. In any case we wouldn't have space for a dual bank system, but I can see it could make sense if you did and your lead acids were in good shape.

[Budawang]

Originally Posted by Westcliffe01

Now, if you add a "real" alternator (like a generator) to your main motor (assuming its possible) then you do 2 things. 1) You get access to much higher kW of power electrically and it doesnt have to e at 12V it can be at whatever voltage the charge controller will accept. That might be 90V to 150V depending on the charge controller max voltage. The charge controller will internally invert the incoming voltage down to the correct voltage and amps needed based on how its been programmed for the battery. 2) you add a more significant load to the main motor so it actually loads up a bit, which is much better than simply being at a fast idle for an hour or 2 a day...

You've convinced me I should look at upgrading my alternator, regardless of whether I install LifePO4, AGMs or lead acids. Can you recommend a brand/model that would do the job?