Battery to Battery charger as best solution- reality check

[Nicholson58]

No matter, you will need an external regulator like the Balmar. Balmar’s latest devices have profiles for Li as well as for AGM etc. ‘This is necessary to avoid cooking your batteries or the alternator. The big high capacity batteries can make the alternator operate at full load too long if they start out low. Most alternators are not rated for continuous full load. For this we set the Balmar at 80% on the monster Firefly set. Note that Li charge cycle has no float. Float will wreck a Li battery. The external regulator also will make more engine power available to the prop.

[Dockhead]

Originally Posted by Pete7

I don't think it is a user option, but instead relies on the multi stage charging profile set to the battery type.

https://sterling-power.com/collectio...-bw-waterproof

However, if the long term goal is LFP, investing £140 now to ensure the alternator output matches the battery type, then that seems a sensible option. Sterling have been making these little widgets for decades in one form or another and they achieve surprisingly high prices second hand.

Pete

The feature is called "belt saver" and allows you to derate the alternator by any given percentage. It's different and entirely independent from the charging profile.



A very useful feature; don't know whether the Sterling regulator has this or not.

[Pete7]

Ok, now understood. That leads on to the question is it needed in this situation if there are 390AH of AGM batteries and a 65A alternator?

Will those batteries tail off the current anyway as they go above 80% SOC?

Pete

[mikedefieslife]

One of the issues for some in going with an external regulator will be having to butcher their existing alternator (unless they can afford to stump up for a brand new externally regulated one) and get busy soldering/de-soldering etc.. to expose the field wires. It's not a simple task for most people.

[Dockhead]

Of course. These are separate issues. Belt Saver limits maximum alternator output to protect the alternator (and/or belt). Charge program regulates voltage and current to suit the batteries.

Originally Posted by Pete7

Ok, now understood. That leads on to the question is it needed in this situation if there are 390AH of AGM batteries and a 65A alternator?

Will those batteries tail off the current anyway as they go above 80% SOC?

Pete

[sailcrazy]

FWIW, we use Trojan T-105s (6 of them) for the house bank, and a Mx-free batt for starting both the eng and genset. Our 85 amp(stock, internally regulated) alternator, solar(Victron Controller) and wind(very minimal input!) all go to the house bank, and a Balmar Duo-Charge (from the house bank to the start batt)recharges the start batt. Suggested and put together by PKYS, it has worked very well for us for several seasons now. We do use a ProMariner 50-3 Batt Chgr (to the house bank) too, when the genset is running.

[john61ct]

For most setups, changing the settings is rare, so yes Sterling's an awkward UI but that is a trivial factor IMO.

The new Victron units will likely be great, but I won't be the pioneer, to early to know for at least a couple years of feedback, unless a trusted expert does in-depth testing reports.

Yes the Kisae DCDC charger apparently works fine and has user-custom setpoints.

Note just like Renogy, does not include VSR internally, on its own will continue to draw off your starter battery regardless of charge source being active or not.

[john61ct]

Originally Posted by Q Xopa

Im not sure what is the desire to 'limit' current? To save the alternator, I assume

Yes but also for bank longevity

With high-CAR chemistry like LFP, if big amps are available they will pull (accept) 10x the maximum current you want to feed them.

[john61ct]

Originally Posted by Nicholson58

No matter, you will need an external regulator like the Balmar.

No. A good B2B makes modifying the stock alternator completely unnecessary.

Of course you can do both if the use case requires it.

[john61ct]

Originally Posted by Pete7

is it needed in this situation if there are 390AH of AGM batteries and a 65A alternator?



Will those batteries tail off the current anyway as they go above 80% SOC?

Yes, it is only the higher demand (acceptance) at **lower SoC** that requires the current limiting.

In this case just to protect the stock alt, with lead banks (other than GEL) you can make as many amps available as you like, the chemistry is self-limiting.

Only cycling in the higher SoC ranges is the same as using a much smaller bank, as far as these issues are concerned.

[john61ct]

Originally Posted by sailcrazy

FWIW, we use Trojan T-105s (6 of them) for the house bank

FLA has such a low CAR, you'd need a 400+ Ah bank at low SoC to stress a stock 65A alt.

High CAR AGM, the threshold is much lower even a single 100Ah could pull (accept) too much current when depleted.

Of course with all lead, the very high demand may only last 10-20min, and ambient temps are a huge factor, so precisely quantifying the interrelated factors requires an artificially controlled lab setup.

[Q Xopa]

Originally Posted by john61ct

Yes but also for bank longevity

With high-CAR chemistry like LFP, if big amps are available they will pull (accept) 10x the maximum current you want to feed them.

Im not sure what you are refering to?

Bank longevity. The good ext Alt regs can be set to be as gentle on your bank as you can set a B2B.

Me and a number of others are trying to say that with an ext Alternator reg, set up-
1. The Alternator gets protected, and
2. the battery gets properly charged.
With a B2B the battery gets properly charged, although often slower than desired.

But the Alternator is not being actively protected by a B2B. For example if the Alt is still getting too hot at 60A it will not reduce the output to let it cool off.

I realise you like B2Bs, as do I, but I cant see the advantage for this application.

[john61ct]

Using a B2B is a valid alternative to modifying the alternator setup.

Of course if an owner prefers to do the latter NP, there are pro's and con's depending on the use case.

The fact that the DCDC is limiting the current demanded by the bank is also protecting the alternator, just as much as an external VR.

You are correct, this is being done statically, not dynamically according to overtemp conditions. Like Balmar's Small Engine Mode, rather than Belt Manager.

The VR doing the current limiting rather than the DCDC, will of course slow down the time it takes to charge to the exact same degree.

Originally Posted by Q Xopa

I'm not sure what you are refering to?

It was a general answer to your general question

> I'm not sure what is the desire to 'limit' current? To save the alternator, I assume

Completely independent of the solution chosen.

[Pete7]

Originally Posted by Q Xopa

I realise you like B2Bs, as do I, but I cant see the advantage for this application.

Me too, there are thousands of yachts happily using AGMs with ordinary automotive alternators. Sterling would have discovered if there was a problem before now by using a A2B.

One way to tell may be to inspect the engine for excessive belt dust or discover if there were previous problems with the alternator and battery charging set up.

[john61ct]

Well of course if the stock alt setup is putting out the right voltage, and the bank isn't pulling too many amps, Bob's y'uncle no need for any of these options.

That is not the OP's situation though.

Originally Posted by sv Libby

We have a beta 65A alternator - internally/poorly regulated.