Mahe 36: Batteries And 12vdc Systems

[careka]

Well Edmund, tell me more about this
"automatic one-way charging relais between them. In at 13,3V, out at 12,8 Volts."

maker, model, and where you got it.

[Cotemar]

Edmund,

I am all ears on these auto charging relays also.
Any pictures or diagrams would help.

[Jef & Marin, Netherlands]

Edmund,
Fantastic idea. Only thing: it seems like a weight increase unless you found a 45 Ah battery with negative weight.....
I can't do this since we now have 3 107Ah AGM's on port, and the original 105Ah starter battery on starboard. They would not match. So for me the option is to replace the starboard starter battery with a small one when it needs replacement.
The original house batteries were gone due to too many cycles, but the starboard one should work 7 years or so since it's not cycled.

[Edmund]

I used this one:

Skillerelé - Biltema (In Norwegian, sorry)

Cheap, working great so far.

Jef: I get an extra 105Ah from the weight of an 45 Ah. But you are of course correct, total weight increases

[Cotemar]

Edmund,

Did you replace the Stb. Emergency Switch with that auto charging relay ?

[Edmund]

No. The relay is mounted betweenthe positive poles on the new starter battery and the old 105 Ah battery. StB engine is connected to the new 45 Ah starter battery.
All original switches are still in place, but the port emergency switch, connecting the port 3x105 Ah to the Stb 105 Ah, is now always in position 'on'.

Edmund

[Cotemar]

I wonder if this setup would work also.

Blue Sea Systems Add-A-Battery Dual Circuit System

[Edmund]

It would. This is the same solution I have, exept that here you also have the opportunity to use your main battery pack as an emergency battery, trough the 2-step main switch.
I would need to replace the main switch to have the same option.

[MKB53]

One comment on using the stb engine. When I did this the max amperage I would get was about 28amp wheras the port engine would deliver up to 95 or so amps. This (port) is what you would expect from a 115Amp alternator. (Standard on the D1-20).
I assume that they have put a lower output alternator on the stbd engine as 115Amp could have damaged the 105Ah battery which would have a max charge rate of 35Amps.

The only impact is that it takes longer to charge up from stbd which wastes fuel (but you get the "free" power to the house bank while motoring).

However if you now have a 45a/h battery it's max charge rate would be 15Amps so you could damage it as well.
Having the house bank there to absorb excess power should prevent this but if you ever isolate the starting battery this could be a problem.

Some of the electrical engineers in the group would know more than I do on this but this is my understanding.

Cheers
Martin

[DotDun]

Originally Posted by MKB53

One comment on using the stb engine. When I did this the max amperage I would get was about 28amp wheras the port engine would deliver up to 95 or so amps. This (port) is what you would expect from a 115Amp alternator. (Standard on the D1-20).
I assume that they have put a lower output alternator on the stbd engine as 115Amp could have damaged the 105Ah battery which would have a max charge rate of 35Amps.

Really? Volvo puts a 115A alternator on a 18hp engine as std equipment? I would guess a 35A would be standard.

[MKB53]

Sure is!

[Oliver66]

Yep I can confirm dot run.
It is 115A on the D1/20 and D1/30.

but 115 is the theorical max they can deliver.
never seen more than 35A on my battery controller.

even for a 300 A battery bank a 115 A charge sounds to much ???

[Edmund]

According to Volvo, the 115A alternator on the D1/20-30 can deliver up to app. 35 A on idle, up to 100 A on crusing speed 2400 RPM, and 115A on max RPM . It will of course only deliver these levels on low battery voltage/discharged batteries. The charging current goes down as the battery voltage goes up.
In everyday life, I rekon the highest alternator ouput will occur when you use your windlass, or when starting one engine when the other one is already charging the batteries.


D1-30 - Engine range : Volvo Penta

[Jef & Marin, Netherlands]

You need not worry about overcharging by a big alternator. The alternator gives out a certain regulated voltage, e.g. 14.4 V.
The battery will accept, at that voltage, a certain current. This current depends on the state of charge of the battery and things like plate surface area and internal resistance (which are coupled to battery Ah size). It will not get damaged by a big alternator.
So you can connect a 115A alternator to an 8 Ah motorcycle battery without causing damage.

The advantage of a 115 Ah alternator is that you can charge even a very big battery bank, e.g. our standard 315 house battery bank. Or even bigger.
I have seen a maximum charge of 80 A, even at modest RPM's of the port engine. However, this is when the batteries are half empty; when they get fuller the current decreases.

One problem of the "stupid" 115 A alternator is that it keeps giving out 14.4 V even when the batteries are already full, e.g. you motor out when you were previously on shore power. In that case the batteries will start gassing by overcharging, and this is not good for them.
To prevent this you can connect a smart charger, e.g. one of the Sterlings, to your alternator. These have 3 charging phases.
This improvement has already been discussed on this thread. It gives the even more important advantage that your batteries charge a lot faster, without harming them. Also the voltage can be adjusted to the battery type (gel, AGM, open acid, maintenance free closed type). And you can connect a temperature sensor which reduces cgaring voltage at higher temperatures; again to protect against overcharging.

Something else: we often go on one engine, at 1700-2000 RPM. STW is then 4.5 or 5 knots. We stop sailing when the boat speed goes below 2-3 knots. Then the 4.5 - 5 knots under one engine is fast enough, taking 1 liter of diesel per hour.
In case we used the starboard engine (nice for hot water), we would connect the house battery with the emergency switch. The charging current will be lower than by using the port engine. The reason is the higher resistance caused by the longer wires from starboard to port.
Now that we have our 470 Watt solar panels charging by the engine is not necessary anymore. This is also the reason we don't have a smart alternator regulator.

[DotDun]

Originally Posted by MKB53

Sure is!

I learned something today....