Electrical charging system questions

[Waltm]

Hi all, I'm the new owner of a '79 Pearson 323. It it currently at a marina with shore power but next year will be on a mooring, hopefully with a small solar system to keep the batteries charged.

On our first sail the batteries discharged within a half hour, with only the radio and nav instruments on. This led to checking out the electrical system prior to replacing the Dihard "Marine/RV Deep Cycle" batteries.

What I found was a dual output charger, a combiner, and an alternator isolator. It appears the isolator is not connected and only being used as a terminal block.
Is the isolator needed for alternator charging? Is this instead handled by the Combiner? Is the Combiner needed with the dual output charger or is it redundant?

Also, does anyone have any opinions on Renogy AGM batteries for both starter and house use, if sticking with the group 31 size?

https://www.homedepot.com/p/Renogy-D...-100/303412933

[Waltm]

Any recommendation on changes that need to be made?

[Mal Reynolds]

A bit hard to provide input based on the info in your post. I'm guessing you have 2 Group 31 AGMs. You don't say how old they are. Hard to say cause of death, but it may be the charger float voltage is too high. Lots of ways to murder batteries.

On the combiner, it depends on how you want to manage the banks. Are these two batteries for house and start? Do you want one bank or two? I'm guessing the previous owner wanted to manage just one bank.

I would recommend installing a battery monitor if you don't have one.

[Waltm]

Sorry for the missing details. They are both Group 31 FLA. One for house and one for start through an off/on/both switch (Blue Sea 5511e) which keeps them separated in the on position. Previous owner was unsure of age but guessed 5 years so I'm assuming they are just old. Water level was low enough to just expose the tops of the plates so filled both with distilled water for now.

It appears the 35 amp alternator charges the start battery directly and the combiner allows charging of the house battery. Isolator appears to not really be in the circuit. I'd probably like to keep them separated so as not to drain the start battery.

I'm still considering what to replace them with, especially the house, as the 'drop in' lithium would appear to get more usable capacity in the same space. Then that opens the whole can of worms with charging the lithium with solar, lead starter with alternator (or separate panel/charger), and DC to DC between starter and house for alternator charger if that is even needed. But that's probably a much longer topic of it's own...

By battery monitor I'm assuming you mean one with a shunt that measures more than a simple voltage meter like what is currently mounted. Would the monitor usually replace the switchable a/b meter or is used in addition?

[Mal Reynolds]

OK, that's helpful. I'd guess the charger boiled off the water in the FLA's over time and that killed them.

On charging, I prefer to charge the house battery from the alternator & solar, then use a DC-DC to charge the start battery. But that's probably more about how my brain works.

On the monitor, yes, a shunt for the house bank to count amps in and out & monitor SOC.

On chemistry, no right answers only tradeoffs. You don't say what your loads are - now or in the future. Autopilots and refrigeration are taxing and would require more capacity. Consideration are if solar is your primary charge source, and how long are you out for (day sails vs long cruises). LiFePO4 is not a great solution for solar as they don't like to sit at 100% SOC. On the other hand you can manage this on a mooring via Victron Remote Monitoring (cell connection), but that's money. AGM & FLA can sit in float via solar for a while with little damage. If you are out for long periods of time, have or plan higher loads then lithium capacity becomes more attractive and you can actively manage the SOC. Also with even with "drop-in" lithium, you will need a new shore charger, alternator and regulator.

Finally, the existing install looks a bit rough. Make sure the batteries are secured and fused within 7 inches. Lithium would require T-fuses. If ring terminals are stacked on a post, stack them largest to smallest toward the nut, and the washer between the nut and the top ring terminal.

[Waltm]

There is currently an autopilot but no refrigeration at this time. Refrigeration would be a 'nice to have' somewhere down the road.

I haven't checked the draw on the various circuits yet. Next year when it's on the mooring I hope to have solar which will be the primary charging source. I'm expecting mostly day sails, some overnights on long weekends and probably no more than one week long cruise during the summer. I would expect to have to re-do much of the charging system for solar but had assumed if the alternator charged a lead-acid battery and that charged the lithium through a DC-DC charger the alternator would be ok. I would hope the lithium house bank would be mostly charged by solar but the alternator would still see the load after they were drawn down and the engine was started. Would it still need an upgrade in this case?


Yeah, the whole wiring system needs to be gone over. While the batteries are strapped down, I didn't see any fuses at the batteries but still have a panel to pull right behind them to investigate. It seems all terminals are automotive style (PVC insulation?) and should be replaced with heatshrink insulated connectors. Nothing is labeled so I need to trace everything out, label, and change connectors.

[Mal Reynolds]

Good info. Chartplotters and radar loads can also add up. Do put together a load sheet to figure out your daily anticipated amp-hrs per day at anchor and underway. This will inform your daily charging (alternator, solar) and battery capacity requirements. You can pull amperage draws from manuals, easier than using a DC clamp meter. There are spreadsheet templates around. I'm attaching one I've used in the past that might be simple enough for you to modify for your loads and charging assumptions.

Given your use case, skip the refrigeration.

Your DC-DC charger solution could work, although charge rate to the lithium will be limited so you won't be able to take advantage of the amazing charge acceptance rates lithium can provide (short engine run times!).

[barnakiel]

A diode or otherwise isolator / combiner is an option. But you can also use a relay combiner that parallels the batteries (the house bank and the engine bank) when alternator starts generating voltage.


Wire it all the way that there is no risk of the alternator ever being run without its + on at least one battery bank. A running alternator, disconnected from the charged load burns its diode bridge immediately.


For charging the banks from the alternator, it is sometimes good to have a better alternator regulator mounted, There are many of this type to choose from. They boost the alt voltage / output to charge the banks faster. Otherwise a plain alt regulator works but it works very slow and you would need to run the engine a long time to recharge a bank depleted by say 25% or more - for hours.


b.

[GordMay]

Originally Posted by barnakiel

...
Wire it all the way that there is no risk of the alternator ever being run without its + on at least one battery bank. A running alternator, disconnected from the charged load burns its diode bridge immediately...

It’s disconnecting the alternator output, from the battery, while the engine is running, and the alternator generating, that is likely to cause a voltage spike [back EMF], and blow the rectifier, and/or the regulator.

[MWGDVC]

Waltm,
Given you are facing replacement of the batteries anyway, and facing wiring upgrades as well, it is a good time in my view to consider upgrading to LiFePo for house loads. I recently saw a “drop in” 12V, with low temp. protection (you need this in RI.) advertised right around $250 for 100 AH.
You mentioned available space being an issue, I have seen several manufacturers offering smaller case “drop ins”. That might permit fitting 200AH in your house battery available space, if not too costly.
Get a battery monitor to display state of charge, consumption rate, and charge rate. I paid around $60 for one that looked identical to the unit sold by Renogy. Unlike lead acid, a volt meter will tell you almost nothing about state of charge of LiFePo.
As you have a 35A alternator, I would size a DC-DC charger not to exceed 50% of alternator output to avoid overheating.
I have a 120A alternator, Balmar regulator, and a Renogy 60A DC-DC charger connected to an AGM start battery. This is capable of charging my house bank. If I were buying again, I would have gone with the 40A DC-DC, as I usually run the DC-DC at ½ output (30A) to keep the alternator at 180f.
But I seldom need to charge using engine, solar keeps me in power, even with refrigeration operating 24 hrs. a day.
As budget allows, add an MPPT solar controller, programmable for LiFePo, and solar panels as will fit on your boat.
As you plan to be at a mooring next year, building a system now for that future makes sense.
Congrats on your new boat!
Mike.