Best way to manage alternator charging on catamaran

[Ted.boender]

Newbie Alert. I looking to make the upgrade to Lithium on my 2019 Leopard 40. I've ruled out "drop in" replacements like Battleborn or Relions. I want the BMS to be able to control the charge. All the big brains tell me this is critical and "the way to go".

I am leaning towards Victron Smart Lithiums 600 Amp Hours with a Victron Smart BMS. I recently upgraded my Inverter Charger to a Victron Multiplus. I also have the Victron Smart Shunt and Two Victron Smart MPPTs for solar.

What is the best way to manage the two alternator charges?

How does one combine two alternators onto the Victron Smart BMS?

[lmxr]

Originally Posted by Ted.boender

Newbie Alert. I looking to make the upgrade to Lithium on my 2019 Leopard 40. I've ruled out "drop in" replacements like Battleborn or Relions. I want the BMS to be able to control the charge. All the big brains tell me this is critical and "the way to go".

I am leaning towards Victron Smart Lithiums 600 Amp Hours with a Victron Smart BMS. I recently upgraded my Inverter Charger to a Victron Multiplus. I also have the Victron Smart Shunt and Two Victron Smart MPPTs for solar.

What is the best way to manage the two alternator charges?

How does one combine two alternators onto the Victron Smart BMS?

Over the years I've seen a few approaches:

Approach 1
External alternator regulator such as those from Balmar, Nordkyn or Wakespeed. The Victron Smart BMS 'charge' output goes to the 'enable' of the external regulator. The voltage sense of the alternator regulator is on the lithium battery.

If you install a relay (charge bus relay) driven by the BMS somewhere between the alternator output and the lithium batteries then you'll have to protect the system from a load dump unless you can guarantee that the alternator is disabled about a second before the relay is opened. An easy an effective method is to use a simple diode charge distributor, which you probably already have, such that the energy can always be dumped in the starter battery. The lead-acid starter battery won't receive a perfect charge profile but in practice it works just fine.

You'll find a system schematic of this approach on the Victron site.

Approach 2
The alternator only charges the starter batteries. DC-DC chargers from starter batteries to house battery, Victron Smart BMS turns the DC-DC chargers on/off. It also drives a relay (charge bus relay) between the battery and the DC-DC chargers. The DC-DC chargers limit the current in the alternator. You can use external alternator regulators but this is not necessary.

Approach 3
Internal regulators, diode charge distributor and a relay (charge bus relay) between the charge distributor and the battery controlled by the BMS. Only do this if (1) you rarely motor for more than a few hours as the charge profile of the internal regulators will overcharge the LFP batteries, which the Victron BMS does not protect against and (2) your alternators have solid overheating protection. The Hitachi ones on Yanmar engines are said to have this, but most do not and burn out sooner or later.

Hopes this helps, feel free to ask questions.

[smac999]

A bms does not control charge... it will only open if there is a problem. The charging source needs to control itself.

[goboatingnow]

The only issue is alternators. Everything else can be turned off when it’s finished charging, a requirement for lithium charging.

In my view given the costs. Changing out the alternator charging regulator for a lithium compatible one is an easy decision.

[witzgall]

Chris from Balmar here. If you use our MC-618 regulators and a centerfielder, you can trigger the two off safely by having your BMC cut power to the "Ignition" leads for both. These wires look for voltage, and the regulator is off until it is connected to + DC, regardless of power going to the actual power leads.

We also have a Alternator Protection Module that will be released before the end of the year. These, coupled with quality alternators with either avalanche diodes or high voltage ones, should protect the alternators from most events.
Quick start guide here - not the QR code is inop right now, as the web page is not live.

Chris

[lmxr]

Originally Posted by lmxr

[...]Approach 1
External alternator regulator such as those from Balmar, Nordkyn or Wakespeed. The Victron Smart BMS 'charge' output goes to the 'enable' of the external regulator. The voltage sense of the alternator regulator is on the lithium battery. [...]

Addition: if there is a relay or switch between the alternator and the lithium battery, the alternator voltage sense should be on the alternator side of the relay, otherwise the alternator will have difficulties to regulate its voltage the relay is opened.

[hjohnson]

Originally Posted by smac999

A bms does not control charge... it will only open if there is a problem. The charging source needs to control itself.

It all depends on which BMS you're using.

I'm looking at building a pack for my boat using a REC Active BMS. If configured appropriately, and combined with the Wakespeed WS500 (or Victron charging sources, and maybe others) it will actively manage the charging source to best manage the batteries.

In the case of the WS500, the BMS is in full control, asking the alternator regulator for more/less current as required. As it approaches 100% SoC, it will ramp down the current while it balances the cells.

It's a pretty sophisticated piece of kit.

[ohthetrees]

Originally Posted by smac999

A bms does not control charge... it will only open if there is a problem. The charging source needs to control itself.

Depends on the BMS. My REC Active BMS controls all my victron stuff (via a Cerbo GX) and separately sends a charge/no-charge signal to my alternator regulator (Nordkyn).

[team karst]

Turning off alt regulators also turns off the tachs on my Volvo pentas.

I also have victron dual solar regs and their shunt based energy meter. Feeding 3x Relions. But, have remote voltage sense on the alts. Seems to work ok. But true, the Relions sit at up to 14.3V whenever either engine is on.

[Cpt Mark]

Do you have or plan to install solar? Do you have or plan to have a generator?

My cat came with a generator. I just built and will install today 840AH of LiFePO batteries. The plan is to add 1200-1600 watts of solar which should be plenty once I'm out cruising in the trades. Not enough in wintertime in Portland Oregon.

I have disconnected the alternator charging from the house (liFePo) batteries completely. If I ever decide I need to use that source a Dc to Dc charger will work.

The 2 engines and generator have 2 agm batteries that start them. 1 battery for each engine and 1 battery that also does the genset. Those batteries get used so little I'm just not worried about them. They also are separated from each other and if need be, jumper cables will work. I am thinking a small 120v ac 2 amp trickle charger on each battery might be worthwhile. Or a small dedicated solar panel.

For me, I just don't see a reason to have LiFePo and AGM's tied together. It's a complexity and failure point I just don't want to deal with.

[team karst]

Originally Posted by Cpt Mark

Do you have or plan to install solar? …

For me, I just don't see a reason to have LiFePo and AGM's tied together. It's a complexity and failure point I just don't want to deal with.

Questions for me? I have two independent solar banks.
Agree with “tied together” on anything with the obvious exception of building large banks.
My 3 sets of banks are isolated by one isolator.
Genset is still a development in process. Right now a honda suitcase

[Ted.boender]

there is some type of relay Leopard puts in the stock boat to control charge from alternator to the AGM starter or AGM house bank.