Isolating batteries

[PNM]

I have two engine alternators, two start batteries and one house battery. The start batteries are isolated/combined/controlled by two battery switches and can be attached to Port, Starboard, or Both engines. The House battery is isolated, with no cabling connected to the start batteries. I want to charge the house batteries while under power, without risking discharge to the start batteries.

Some of the new isolators handle 3 battery banks, but don't say anything about 2 alternators. I wire my alternator outputs directly to the engine associated starting battery (ie Port to Battery 1, Starboard to Battery 2).

I think I can just put a diode between Battery 1 and House to keep the House from discharging the #1 battery, but then the House does not get charged if the Port Alternator fails.
Same for Battery 2.

If I cruise with the battery switches in the both position, either engine alternator would provide charge to all the batteries including the house, but then the two alternators would be competing - is that a good idea?? Seems like if one alternator kicked in first, the second alternator would sense high voltage and not kick in, leaving the charging of 3 battery banks to a single alternator.

Any suggestions would be appreciated.

 

[SteveK]

Using switches to charge depleted house bank saw higher amps into house bank than one ALT can produce.
Nearing full charge one ALT may/will drop off. Also I do have it setup thru DC2DC so that may keep ALT fooled longer.

 

[tiltrider1]

Current thinking is alternators to house bank and DC to DC charger to start batteries.

 

[DDW]

The only practical way to get two alternators to share the load is to have regulators designed to do that. Balmar and Wakespeed. They communicate with each other and do the right thing.

 

[Delta Riverat]

I'm going to use (2) Victron Argofet isolators. One for the new Lithium house bank that is charged with starboard engine alternator with external regulator and the other for the LA starter batteries that get charged with the port engine stock alternator.

 

[SteveK]

Current thinking is alternators to house bank and DC to DC charger to start batteries.

Of course as long as you have an outside regulator, if not then to non LFP battery and DC2DC to LFP house

 

[READY]

I'm going to use (2) Victron Argofet isolators. One for the new Lithium house bank that is charged with starboard engine alternator with external regulator and the other for the LA starter batteries that get charged with the port engine stock alternator.

Will your external regulator for your lithium/starboard eng protect the alternator if the BMS shuts off charging? I am in process of doing something similar. I have a wakespeed regulator and the victron argofet but still thinking about the best way to set up my system. I don't plan to touch my starboard setup (small alternator and Group 4 AGM). Will put the "fancy stuff" on the port engine with a high output Balmar. It already has an older high output alternator and two V belts so this makes things easier.

 

[Delta Riverat]

Plan to use new Balmer regulator and set field so low that the batteries will never get fully charged. If I want to get a full charge I'll do it with the inverter charger either at shore or with generator. My alternators are only 40 amp (stock) and I need to protect them from over current (overheat).

 

[Portage_Bay]

The only practical way to get two alternators to share the load is to have regulators designed to do that. Balmar and Wakespeed. They communicate with each other and do the right thing.

There is at least one more device to accomplish the task. The Sterling Alternator to Battery Charger. If starting from scratch with a pair of internally regulated alternators this could be a good way to go. If battery chemistry of the start and house banks differ then a DC to DC charger might be needed. Ben Sterling is very helpful with questions.

The output from both alternators goes to the Alt to Batt charger, the charger does 3 things.

1. It lowers the apparent voltage to the alternators "fooling" them into higher output for longer duration.
2. Combines the alternator outputs.
3. Ensures in the early charging phase the start batt gets priority.

I installed this on a pair of Cat OEM 55 AMP internally regulated alternators. The original set up was stbd charged house, port charged start. Net charge rate to the house bank has greatly increased. It's worth reading Sterling's write up on the device

 

[PNM]

Thanks for all of the expertise and suggestions evident in the responses.

I read an interesting blog from a Combiner Company Site. KISS was the primary message.

I'm thinking - use my current switching arrangement to combine the two start batteries by keeping the switches in the both position, then attaching one alternator (mabe low output) to the start batteries.

Then attaching the other alternator (mabe high output) to the house bank.

I could use a manual switch to combine the house with the starting banks, if anything abnormal happens while cruising - like the Starting Battery Engine/Alternator fails! Or, the House Engine/Alternator fails.

This sure sounds simple - am I missing something??

 

[Nepidae]

I may be coming late to the party but having to utilize switches to change your charging profile seems like something destined for failure or trouble.

You didn't state how you used your boat or the size of your batts, just the number was mentioned. Do you anchor out a lot? I would think with 1 house batt that you probably don't. Are you looking to change any of this?

IF you wanted to do away with your switches then you could consult with Balmar and utilize some of their equipment.

We anchor out occasionally and I didn't want to have to deal with switches. Our house bank is 6-L16 AGM batts and without charging will last about 2-3days. We have 2 - D4 AGM engine batts, probably overkill but we had the batts before the Balmar equipment.

The Balmar equipment we have is 2 - 125A alternators. These are V-belt drive. We have 2 - 614 regulators and then 2 duo-chargers. They are connected to a centerfielder. This has the intelligence to charge where the charge is needed. No switches or dials.

So, we anchor out. My Victron BMV-712 Smart batt gauges gives me the SOC status, among other things, on the batts providing a check anytime I want since I can check the status on my phone or tablet,

BTW, we also have a Victron Multiplus 3000/12 charger/inverter which handles our needs very well.

We added solar after the Balmar stuff was installed and I have Victron equipment to handle that. IF interested in that aspect, let me know, PM and we can discuss.

Hope this helps.