Efficient Battery Charging with Internally Regulated Alternator???

[TradewindSailor]

I have a 450 amp hr house battery bank and twin cranking battery banks ...... all wet acid. I have connected them with relays as I had 0.3v drop using the standard manual isolator toggle switch, and only 0.1V with the relays.

I'm running two new 3YM30's with the standard 60 amp internally regulated alternators. The regulation peaks at 14 V.

My problem is that although the charging starts at about 50 Amps, within half an hour it reduces to 25 amps without the voltage exceeding 13.5V, at which point I run my refridgeration system (large holding plates) that draws about 35 amps .... the charging settles down to about 15 Amps input into the house bank.

The cranking batteries are always near full .... and there is less than 0.1V difference between the battery banks.

In an ideal word I would expect the regulator to charge at peak current .... say 50 amps until 14 volts is reached and then stay there until its 80% charged where it then settles down to 13.5 V.

At the moment I believe my charging system is pretty inefficient. I've also had similar charging characteristics with an external 3 step regulator on a 100 amp alternator on another yacht.

Any ideas as to improving the charging system? ..... or is this typical?

As it stands at the moment I think I'm damaging the big house batteries as they never seem to get up to 14V.

Any comments will be much appreciated.

Cheers

 

[halcyon]

What alternator is charging what battery bank, can you expand on your system.

Brian

 

[William_H]

I suspect that your system is working pretty well for what it is.
I don't really think your batteries will suffer too much at only being charged to 13.75 volts.
Presumably your alternators are sensing at the alternator output. The additional current drain of the fridge may be causing a volt drop in the wiring between the alternators and the battery/fridge. This could possibly be improved by fitting heavier wiring in the common path or by taking the fridge current supply directly from the alternator outputs (via relays).

There are schemes where you lift the negative of the regulator sensing above ground with a didoe so raising the charge voltage by .7 volt but this can be fiddly making connections especially on 2 alternators.

So the last option which will cost, is to invest in one of the new design of stepped battery chargers which run on the 12v supply from the alternator/ cranking batteries.

This is a bit like a VSR except that it takes the 12v and switches it rapidly to generate about 15 volts which is varied according to the voltage of the battery to give the classic 3 or 4 stages or charge including the rapid bulk charge. It will obviously draw a lot of current from the alternators being the battery charge current (at 15v) at an efficiency of about 90%. Thius wil bulk charge your batteries faster.

You have to decide if you really need it. Much depends on the engine running time in a cruising day, if you have solar boost and if you have a shore power charger. I think I might be satidfied with what you have. good luck olewill

 

[tinkicker0]

You charging system is fine, a good 3 stage charging is the way to go.

If your alt walloped 50A in, then cut off, you would not have a well charged battery.

Bit like fitting 40 people in a mini, first few go in fast, the next have to go slower while everyone moves their bodies about and the last ones go in slow while everyone reconfigures arms and legs.

If the lights go out during the night, time to get the tools out, if they don't, then don't mess. It will only give you an ulcer. /forums/images/graemlins/grin.gif

 

[TradewindSailor]

Thanks for all the comments.

Halcyon ..... I have two 60 amp alternators, one on each engine. Each unit charges it's own cranking battery .... and the house bank when manually switched via the relay. This means that both cranking banks and the house banks are common when I run both engines, but I normally charge with only one engine ...... leaving the other engine's cranking battery isolated.

I usually charge with one engine at 1200 rpm (which gives a max of about 55 amps). I let the batteries charge until the chare current is down to about 24 amps and then switch on the refridgerator compressor until the freezer plate is down to -22 deg c (about an hour or so ...... depending on how many beers are cold /forums/images/graemlins/cool.gif)


I guess my best solution is going to install 4 x 135 Watt solar panels ..... save the diesel and have equalisation potential to-boot.

Many thanks

 

[halcyon]

The 60 amp alternator is not rated as 60 amp battery charge, but 60 amp power supply. So you may not see your full 60 amp, also when you switch on the fridge, 35 amp, this will take most of one alternator output, hence your low voltage.
Try linking both alternators to the service bank, this will counter your fridge, increase your charge current and voltage.

You can use two suitably rated bi-directional VRS's, one connects say port engine to service, the other starboard engine to port engine battery, I know it sounds odd. The port engine will charge it's battery then the service battery, star'd will charge it's battery then combine with port engine.

The odd layout allows you to also remotely start either engine of the other engine battery, without touching the service bank. It will provide alternator redundancy should one fail, and allows both alternators to charge the service battery. It can also allow your solar panel to charge all batteries.

Brian