Automatic Charging Relay question

[vpbarkley]

We have two battery banks - a house bank and a start bank. The start bank handles starters, windlass and bow thruster.

I understand that an automatic charging relay is used to enable charging multiple battery banks from a single source.

We have three charging sources: solar, alternator and battery charger

Do we need three automatic charging relays?

Thank you.

[Sailmonkey]

Nope, only one between the two banks

[stormalong]

You need one ACR to join two battery banks. Charging sources are irrelevant.

Just curious, which bank is your alternator connected to? Do you have an external alternator regulator?

[vpbarkley]

If a single ACR is used that means the alternator, battery charger and solar MPPT are connected together at the ACR. Interesting.

I can't say which bank the alternator is connected to. It's a very complicated and poorly thought out setup, created by several people over the years. I'm in the process of simplifying it.

We have a 160 amp alternator with a separate Balmar regulator.

[stormalong]

Originally Posted by vpbarkley

If a single ACR is used that means the alternator, battery charger and solar MPPT are connected together at the ACR. Interesting.

I can't say which bank the alternator is connected to. It's a very complicated and poorly thought out setup, created by several people over the years. I'm in the process of simplifying it.

We have a 160 amp alternator with a separate Balmar regulator.

Charging sources are connected to a battery bank. The ACR connects battery banks when one of the banks' voltage rises above a threshold that indicates that it is being charged. Which bank the charging sources are attached to is independent of the ACR. The reason I asked which bank the big alternator is attached to is that in an ideal setup all charging sources should be attached to the house bank and the engine start bank should only be used to start the engine. In that way the start bank is never discharged by any other load, such as the windlass - it is always available for the engine start regardless of what happens to the house bank.

[NYSail]

With a beneteau if from the factory your alt goes to the starter. However when the new alt was put in hopefully they put it to the house bank...... easy to trace just lift the hood, go to back of alt and follow the big red wire.
I am in the process of changing out the beneteau configuration for the most part and have a charging buss next to Mt house where the alt, solar and shore power lead to. I have an acr from the house back to my starter...

Good luck
Greg

[chrisr]

being a cat, we have 2 VSRs - one for each engine. these switch engine alternator between the start batteries (one on each engine) and the house bank.

start batteries only start their respective engines - nothing else. everything else is on the house bank

wind & solar both feed into the house bank.

it's normal for us to have 4 charging sources feeding into the house bank (if we are motoring on 2 engines). technically could even be 5 if we had the generator running as well, feeding the battery charger...but that would be overkill !

cheers,

[deblen]

This link may help. Cheers/Len


https://forums.sailboatowners.com/th...usings.137615/

[vpbarkley]

Our start bank has three, identical, 92 Ah, AGM batteries. Two are located at the bow thruster and one at the main engine.

The start bank handles high amp, short duration loads: engine starter, generator starter, bow thruster and windlass. The engine is running when this bank is used.

The house bank sees low amp, long duration loads: autopilot, pumps, refrigeration, navigation, lights, etc.

[MJH]

Originally Posted by vpbarkley

We have two battery banks - a house bank and a start bank. The start bank handles starters, windlass and bow thruster.

I understand that an automatic charging relay is used to enable charging multiple battery banks from a single source.

We have three charging sources: solar, alternator and battery charger

Do we need three automatic charging relays?

Thank you.

No, just the one ACR between the House and start banks.

~ ~ _/) ~ ~ MJH

[CarinaPDX]

As others have said connect all charging sources to the larger house bank, and they will properly regulate charging for that most important bank. Only use the starter battery for starting. But I would not at this point in technology development use a simple ACR to connect the starter battery to the house battery when charging as it will tend to overcharge the starter battery. Instead buy a DC-DC battery charger that will tailor charging of the starter battery to its needs. Also, just in case, rig a manual select switch for the starter motor and leave it on the starter battery, having the house for an emergency start with the switch. Implicit in all of this is a separation of the alternator and the starter motor; all charging sources should go separately to the house battery and all consumption should also go separately to the battery. And be sure to use fuses and shut-off switches as appropriate to protect the system.

Greg

[vpbarkley]

We now have AGM batteries for both the house bank and the start bank.

The charging profiles for all three charging sources are set for AGM batteries.

So there's no need for a special, DC to DC battery charger for the start bank.

I chose this arrangement to simplify charging on the boat.

[CarinaPDX]

Originally Posted by vpbarkley

We now have AGM batteries for both the house bank and the start bank.

The charging profiles for all three charging sources are set for AGM batteries.

So there's no need for a special, DC to DC battery charger for the start bank.

I chose this arrangement to simplify charging on the boat.

Not quite true: you just solved one problem (different battery types). The other problem is that it will take a lot longer to charge a house battery than to top up a starter battery. In a 3 stage charger that means the starter battery will be charging at the elevated absorption voltage long after it is charged, which is usually not ideal for the battery. A DC-DC charger will cut off charging earlier for the starting battery, according to its needs.

That said, the better shouldn't be the enemy of the good. Your system will work fine, and I suspect that the greater usage of the house bank will age those batteries faster than the prolonged charging will age the starting battery so in practice if you replace all of them at the same time you may never see any difference. Others have been critical of isolator diodes, usually because of the slight energy loss involved, but in practice they work well, are simple and robust, and the loss is negligible [and the starter battery will also get overcharged]. Chasing the ideal system has diminishing returns...

Greg