Charging Question

[robmurray]

I know that batteries determine what current they will accept from the alternator, depending on their state of charge. However, can anyone answer the following? Lets assume that my batteries are taking 25amps from my 100Amp alternator because they are reasonably well charged. If I then apply a load on the batteries of say 10amps, is this additional load provided by the alternator (so the batteries still get 25) or does it effectively reduce the input to the batteries (so they get 15)? Help much appreciated.

 

[catmandoo]

Depends on what voltage your alternator regulator is set at and where such voltage is measured . If you have a smart regulator /charger then theoretically the batteries float at the set float voltage and all amps come from the alternator if it has the capacity to do so . If you don't have a smart one then if battery sensed or machine sensed regulator will switch on or off alternator field current depending on voltage level at sensing point

 

[halcyon]

It's a voltage thing, depending what sort of load you apply. If the alternator holds it's voltage, then your battery charge will be the same, and the 10 amps supplied from the alternator. But the load could be a easier path than the battery, so the voltage drops a little. This will reduce voltage to the battery, and thus the amps that you can push in, so you will see a drop in charge amps.

Try it and see what happens, is the easy answer.

Brian

 

[Anonymous]

I would be amazed if you would even notice the effect on the charging rate of the batteries - in your example the batteries will still be taking a charge of 25A and the extra 10A will be provided by the alternator so the alternator is now providing 35A.

This is true for simple, standard charging systems, not only when using alternator boosters such as Sterling.

If you started to draw very much higher currents approaching the limit of the alternator or wiring, that would be different, but at the level you have given, no problem.

 

[Gypsy]

I concur with Lemain but with the caution that the motor must be running fast enough for the alternator to be able to put out the extra current. Remember the max output specified for an alternator is usually at near top of its revs range (you need to see the output curve of the alternator) and it is also subject to the pulley size/ratio installed. If you have a good match of pulley to engine you should be able to achieve max output of the alternator at cruising revs, not max engine revs.
Ray

 

[jimbaerselman]

With a smart voltage regualtor, charging voltage at the batteries will remain constant, and the alternator will push out the extra 10a, raising its output to 35a (assuming sufficient revs)..

Using the voltage regulator within the alternator, the extra load may drop the voltage at the battery slightly - so your charging rate may drop an inch or two. Not significant. Say 33a to 34a total?

 

[davidbains]

On a related matter. I have a smart charger which seems to work well.
I recently fitted a VSR to shift excess current over to the windlass battery which is now well charged, so much so that it occasionally send some current back.
Only trouble is, starter battery now a bit reluctant to spin the engine some days!!
I used to KISS but now I'm confused.
Incidentally the weather in the Adriatic seems as bad as in the UK this week.

 

[Richard10002]

Not sure if this should be a new thread, but here goes:

I have 3 battery banks - 2x110Ah Domestic, 1x110Ah Engine, 1x200Ah Bowthruster & Inverter.

I also have a Sterling Battery Monitor with display - it shows Ah in and out for the Domestic Bank only. It shows volts for all 3 banks.

With the engine running, according to the monitor, each bank charges at around 12.9v to a max of 13.8V. The charging starts at the lower voltage and increases to the maximum.

The domestic battery charges at anything from around 35Ah down to around 1Ah, depending on how discharged the bank is. Usually, when it gets charged to around -25Ah, the input is down to around 4Ah or so.

The domestic and engine banks reach 12.7 or 12.8V most time I charge, (assuming I leave the engine running long enough), but the Bowthruster bank rarely exceeds 12.5v, and is quickly down to 12.0V or so, even if I am only using the inverter to power a laptop.

2 Questions - will I benefit from a smart charger, and where/how is it fitted.

What might be wrong with the bowthruster battery, which was new 12 months ago, but might have been completely discharged at some point in its' short life.

Many Thanks

Richard

 

[captainslarty]

Good Morinh Richard
Please supply more details of how the batteries are connected in the system, any split charging systems vsr´s etc.
If they are all wired together the readings are probably correct due to cable sizes. Not working well, but correct readings.
Joe

 

[jimbaerselman]

As the Joe says, we really need a layout diagram showing where your diodes are, where voltages are sensed from, and what length and diameter your feeds are.

At this stage I'll hazard a wild guess that 'bow thruster' bank is near the front of the vessel, with short, fat feeds to the bow thruster, and a long, thinner feed from the three way splitter diode (which I'm pretty sure you must have) which charges it.

If so, there's quite a strong possibility that the bow thruster lot is getting half a volt less than the rest due to resistance in the charging line.

You mentioned in a thread elsewhere that you used about 60ah a day. Above, you mention max charge voltages of 13.8v. Almost certainly, you'll have a significant gain from using a smart charger. It'll raise your charging voltages at the battery to some 14.4v when the batteries can take that charge.

Given three banks, installation isn't necessarily straightforward. Many smart chargers sense only one battery bank (domestic) and distribute to all via a separate diode splitter. Some sense multiple banks, but still distribute the same way. This implies that some batteries (usually the starter) receive more charging than is good for their water supplies . . . while others may be starved if their lines have higher resitance than their neighbours.

So it's often sensible to (could be automatically) switch the charge from your starter bank to one of the other banks once the starter battery is up to speed. Also, if cable runs to different banks have significantly different resistances, some re-wiring may be needed to match them.

One way or another though, you'll significantly shorten your engine running time to re-charge, and extend you battery life too.

Google 'alternator regulators' to find a host of suppliers - and all their horse***t about their own 'unique' advantages. In fact, they're all much of a muchness making a lot of noise about trivial differences. Adverc and Sterling are two protagonists who market entusiastically at boat shows. IMO, little significant difference. Slightly more flexibility and prettier lights on the Sterling. I've used Adverc for 10 years.

 

[Anonymous]

Richard, It is almost certainly due to diode drops from splitters as the volts are exactly what you'd expect if that was the case. Yes, a Sterling or Adverc booster is an answer - the 'cheap' option or go for a Balmar alternator and controller for a much better system, properly designed and built for a marine engine room environment - and keep the existing alternator as a spare. You will never get full charge while you are running like this unless your mains charger has a sense wire, perhaps, and will take them up to 14.4 or more, for a while at the end of charge?

My guess is that the bowthruster battery is connected via a diode from the domestic or engine battery giving you two diode drops, hence the lower voltage. You need to sort that out as you will never get more than 30% charge or so and will damage that battery (if it has not already been damaged). Have a look around and see if you can't connect the diode going to the bowthruster to the alternator output instead of the other battery. That will help pro tem.