Battery to battery charging

[Pye_End]

I think you find find the quote in post #35 originates from Sterling sales literature, hardly non-biased and it's nonsense to say that batteries only get to 80% using a VSR. The quote has been posted on various internet forums, where some people believe everything they read as gospel.

You seem to have all of the answers you need, so i'll leave you to it.

I'll also ignore your facetious comment "(is there a reason you type 'a' not 'A'?)" where it belongs.

Sorry you feel that way. All absolutely genuine questions and nothing derogatory or facetious meant. Just an over enquiring mind, who understands better through 'nuts and bolts'. We are all built differently.

 

[Pye_End]

You need to understand how batteries are used in small sailing boats like the OPs Sadler 26. The typical daily consumption when cruising (assuming no fridge) is +/- 40Ah (roughly double with a fridge). This about 50% of the usable capacity of a 100Ah battery such as the OP has. The challenge is how to replace this. The limitation using the engine alternator is the acceptance rate of the battery which is typically 10A going from 50% SOC up and reduces the closer it gets to full. That is what underpins Sterling's 80% claim. It is not that the alternator cannot charge to full, but as pointed out in post#39 the engine is simply not run for long enough. Earlier the OP said he rarely sees more than 8 amps from his alternator. That is not unusual. I have a 70A alternator and a 190Ah bank and rarely see more than 12A for any period of time. My previous boat had 300Ah and a 115A alternator and rarely saw more than 15A. A B2B will not change this. The charging (bulk) voltage on a 3 stage for an AGM is typically 14.4v - the same as the alternator. The B2B does have a float charge, designed for when the charge source is on permanently. That is largely irrelevant with a sailboat engine as it is only running for short periods when the battery is less than fully charged.

As I suggested earlier to get better use out of the house bank doubling capacity means that not only does the buffer last longer, but the charge it can accept is higher as I describe above. The most important thing is to add generating power when the engine is not being used. the 2 obvious are solar and shorepower. As I said earlier, starting your cruise with a fully charged bank is the key not only to getting the best out of the batteries, but to increase their life because they will spend most of the life close to fully charged and rarely if ever go below 50% SOC. I use shorepower and with my last boat that did a lot of 2-3 days away with no charging other than the engine would take up to 2 days on shorepower to get to float. Batteries were still good after 6 years. If not on shorepower then solar can achieve similar results.

Of course lithium changes all this because it has effectively no acceptance rate constraints when partially discharged and the B2B is one way of controlling the charge to protect the alternator. Its 3rd stage may well come into play because unlike LA it is possible to fully charge with relatively short periods of engine running.

Yes I can appreciate that.

Thinking to my own situation, I can regularly motor for 8 hours or even 24 hours during the year. I also sometimes sail for long periods, so capacity and charging are really useful. I don't have regular access to shore power, and the limited space on the coachroof supports a 60w panel which takes a little while to top the batteries up - useful for the start of a trip (at least in the summer), but less use for the rest of the trip. I run a fridge. My yacht usage maybe doesn't fit the profile you have in mind. How does this compare with the OP?

I have maxed out space for battery capacity for now (currently 160Ahrs). Another problem with us small boats is space.

I use an AB charger with open LA. Absolutely no idea what quantifiable benefit I get from it, but can say it regularly goes to float voltage.

Regarding the Beta 40A alternator - all I can find so far is an output of 14v on a spares website but do not know if it correct. Do you know that it is 14.4v, or is this an educated guess? Sorry to keep on about this, but as you say, if they both output 14.4v then I agree the answer seems pretty conclusive for this battery just on this fact alone (maybe why the likes of Sterling and Nigel Calder say the bigger benefit is for open lead acid at 14.8v).

The lithium option certainly looks interesting for the future - I look forward to jumping on it at some point, and I wonder if it is worth looking at the uprated Beta alternator first, and then choose a B2B charger of higher spec to feed them, especially on a staged install. It also looks to me as though an AB charger becomes redundant with this change in technology - but would also value your thoughts on that.

 

[Tranona]

8 hours is unusual, never mind 24 (although I once did over7 days under motor in delivery mode across the Med). Even 8 hours motoring may not charge your 160Ah from a "normal" days usage on a small boat because the acceptance rate is so low. The 14.4v of the Beta alternator is what I was told when I bought my new 30 and was sorting out what batteries and charging to install.

As to usage patterns that really is individual although one can make a good guess at a typical what I call weekend sailor. 10 weekends a year plus a longer cruise might be a reasonable starting point. Lots of data to suggest less than 100 engine hours a year is typical, as is the 40Ah for a small boat with just instruments VHF, tiller pilot and lights. Add 30-40Ah for a fridge, Extra for night sailing. You can do your own usage audit using your battery monitor (if you have one) and then work out your daily deficit after your normal engine running and or solar input.

Based on what you say you are simply asking too much from your battery and charging - assuming your fridge consumption is similar to mine. I had almost twice your capacity which in usable terms is 2 days away from charging. You only have one. Whether you use an AB to boost the output from your alternator or a B2B the fundamental problem does not change. This is where lithium will change the fundamentals, first by doubling your capacity for the same space and second because of the high acceptance rate up from 8A or so to 20 or even 30A through the B2B depending on the capacity of your alternator.

 

[Robin Cassells]

I asked Nigel Calder about this, and it would seem that the difference would be minimal, but beneficial - in his esteemed opinion:

"Robin,
In principle, given that the house batteries will be cycled on a regular basis a multistep charging algorithm from a B2B charger will be beneficial. In practice, this depends on boat usage, level of discharge, the level of alternator output, running time of the engine, etc. In other words, if this is a weekend sailboat with a small alternator and limited systems the B2B will likely not make much difference over the VSR, but if the systems are being worked harder it likely will.
Nigel"

This agrees with the general opinion in this thread that there may be better ways to spend the money. But it can't do any harm and is likely to reap benefits.

Is it worth the money? Only the OP can decide that.

 

[PaulRainbow]

I asked Nigel Calder about this, and it would seem that the difference would be minimal, but beneficial - in his esteemed opinion:

"Robin,
In principle, given that the house batteries will be cycled on a regular basis a multistep charging algorithm from a B2B charger will be beneficial. In practice, this depends on boat usage, level of discharge, the level of alternator output, running time of the engine, etc. In other words, if this is a weekend sailboat with a small alternator and limited systems the B2B will likely not make much difference over the VSR, but if the systems are being worked harder it likely will.
Nigel"

This agrees with the general opinion in this thread that there may be better ways to spend the money. But it can't do any harm and is likely to reap benefits.

Is it worth the money? Only the OP can decide that.

At least Nigel agrees with some of us.