Batteries and charging

[William_H]

Float voltage is a permanent on charge voltage, charging from the engine will not need this as running time is limited by fuel tank.

The other thing to remember is that the voltage you see when charging from the alternator is not DC, it is half a sine wave, the top section above the DC voltage is the bit that charges the battery. So say the DC meter says 14.2 - 4 volt, the peak measured on a scope can be 15.5 - 16 volt, hence the high gassing with high levels of alternator boost.

It's the pulse above the DC voltage, that allowed us to fully charge a standard flooded battery with a mains charger running 14.3 volt.


Brian

Well actually the output of the alternator is the result of 6 half cycles squeezed together in time. Each AC cycle being full wave rectified has in effect 2 pos half cycles
for each ac cycle. But then during that one ac cycle you get another 2 identical versions superimposed each at 120 degrees apart. So actual DC out is much closer to smooth DC than just one half cycle. However as you say this waveform can confuse a digital voltmeter but if it is measured while connected to a well charged battery you can measure accurately what you need to know. ie charge voltage.


Quote Originally Posted by William_H View Post
However that will not help your engine battery connected to the alternator at 14.2 volts.
The Sterling blurb says there's a diode in the starter path, so that will at least cut the voltage a little.

Pete

I doubt this and surely only if you fit a diode between alternator and engine battery. I think the idea of AtoB charger is that you do not disturb the standard system ie alternator to engine battery but simply connect to it. The concept of charging the engine battery for a period then starting to charge the domestic battery via AtoB charger is just advertising spiel for saying that the AtoB does not start to work until engine battery recovers its voltage up to probably about 13.0 volts. ie just like a VSR. And if engine battery drops in voltage the AtoB will stop sucking current until it recovers. olewill

 

[pvb]

Quote Originally Posted by William_H View Post
However that will not help your engine battery connected to the alternator at 14.2 volts.
The Sterling blurb says there's a diode in the starter path, so that will at least cut the voltage a little.

Pete

I doubt this and surely only if you fit a diode between alternator and engine battery. I think the idea of AtoB charger is that you do not disturb the standard system ie alternator to engine battery but simply connect to it. The concept of charging the engine battery for a period then starting to charge the domestic battery via AtoB charger is just advertising spiel for saying that the AtoB does not start to work until engine battery recovers its voltage up to probably about 13.0 volts. ie just like a VSR. And if engine battery drops in voltage the AtoB will stop sucking current until it recovers. olewill

I often wonder whether anyone bothers to read the Sterling manuals before giving their learned opinions on how they think the products actually work!
.

 

[halcyon]

Well actually the output of the alternator is the result of 6 half cycles squeezed together in time. Each AC cycle being full wave rectified has in effect 2 pos half cycles
for each ac cycle. But then during that one ac cycle you get another 2 identical versions superimposed each at 120 degrees apart. So actual DC out is much closer to smooth DC than just one half cycle. However as you say this waveform can confuse a digital voltmeter but if it is measured while connected to a well charged battery you can measure accurately what you need to know. ie charge voltage.

The rotor is a number of soft iron claws that are interlaced around a electro magnet, giving a series N & S bands, the rotor rotates inside a stator, made up of the coils giving a 3 phase AC output, each rotation gives around 8 pulses x 3 phases so 24 charge pulses per revaluation.

The battery starts at a low voltage, the charge pulse is a lot higher, the charge current is basically the area of each pulse above the battery voltage. As the battery is charged the battery voltage rises, so the area above the line reduces, so the charge current reduces,

Increasing regulator voltage increases the area of the pulses above the line, so charge current at higher battery voltage.

Brian

 

[charles_reed]

I forgot to mention that the alternator is battery-sensed, although that doesn't directly relate to your answer.

My concern about the "smart" charger - at least the Sterling one - is that it doesn't actually lower the float voltage to a sensible float level. It just stops boosting it. I don't know much about the regulators that you open up the alternator in order to fit, but my understanding is that they generally augment, rather than replace, the original one. So when the "smart" regulator thinks it's time to float, will it just hand over to the (too keen) basic one?

I don't want anything that involves manual switching. It seems like a retrograde step when everything else I'm fitting is designed to make things effortless - and one day someone will forget it and ruin hundreds of pounds worth of battery.

Pete

Not much you can do about single source charging such as an alternator - whilst many "smart" controllers do battery-sense, they usually only do it on one battery. It's perhaps overkill to have an alternator per battery-bank, but that would, IMHO, be logical. Certainly you can justify a mains smart charger for each bank, rather than a 2 or 3 outlet one (which again only sense the charge in the most well-charged battery).

I too consider Sterling's descriptions of their gear as a triumph of marketing doublespeak of engineering commonsense. I don't believe though there are any direct misrepresentations and even, occasionally, buy his products.

 

[William_H]

I often wonder whether anyone bothers to read the Sterling manuals before giving their learned opinions on how they think the products actually work!
.

Humble appologies PRV I am guilty as charged but how am I wrong? olewill

 

[William_H]

The rotor is a number of soft iron claws that are interlaced around a electro magnet, giving a series N & S bands, the rotor rotates inside a stator, made up of the coils giving a 3 phase AC output, each rotation gives around 8 pulses x 3 phases so 24 charge pulses per revaluation.

The battery starts at a low voltage, the charge pulse is a lot higher, the charge current is basically the area of each pulse above the battery voltage. As the battery is charged the battery voltage rises, so the area above the line reduces, so the charge current reduces,

Increasing regulator voltage increases the area of the pulses above the line, so charge current at higher battery voltage.

Brian

Yes quite correct except my point was that the humps of charge pulse get amalgamated together so that the raw humps might only be 10%above the continuous collective of the 3 phases all full wave rectified. Compare dperhaps to an old half wave mains charger where only one polarity of the AC cycle is in the output so voltage rises from 0 to max then down to 0 then stays at 0 for the next half cycle. So in this case current definitely goes in pulses as you say dependant on inherent voltage of the battery whilst in an alternator output the continual current is possibly above the inherent voltage of the battery punctuated by additional pulses 6 for every AC cycle or 24 per rotation.
Sorry if i seem argumantive but it might help someones inderstanding olewill it all depends on battery charge state.

 

[sailinglegend420]

....I'm not convinced that constant charging at 14.2v will wreck an AGM battery - after all, AGM batteries are now being fitted to cars, which often have alternators regulated at 14.4v.

Charging ANY battery at less than the manufacturers recommendations will shorten its life!

Deep cycle batteries need to reach their gassing voltage (at least 14.4 volts - depending on temperature) to stir up the electrolyte and stop stratification, and burn off as much lead sulfate as possible that forms on the plates when the battery discharges. When nearly fully charged they must drop down to a float voltage to stop too much gassing. Hence multi-stage regulators are needed to set these voltages for each kind of battery.

All this was not important in starter batteries in cars. The alternator was designed to run the car electrics and not worry about the starter battery which only takes about 10 minutes to recharge. Even modern alternators that claim 14.4 volts will quickly fall way below this with the car loads and with temperature compensation. As the engine heats up the charge voltage falls off so the starter battery isn't held at or above its gassing voltage for too long.

Many boats come with a cheap standard automotive alternator with an internal regulator that is only designed for charging a start battery. This alternator regulator will not properly charge a deep cycle house bank, so the battery capacity and life will be severely reduced. Marine alternators will be much more expensive and can be controlled by an external multi stage regulator. They also may have a “Hot Rated” output that will give a more realistic idea of their true performance when under continuous heavy load.

So if you do use a Sterling Alternator to battery charger beware of the potential problems. It works by making the alternator work flat out to produce a high current and low voltage. This makes it overheat, so it's effective power output falls away very quickly. If the engine is already old then this treatment may kill the alternator quickly. It would be better, and cheaper, to get the alternator modified to accept an external regulator with sensors to detect the alternator temperature and the batteries temperature. The "best practice" solution is a "Hot Rated" marine alternator that will give its rated output even when working long hours to recharge a depleted deep cycle battery. For most it would also be an opportunity to fit the highest current alternator that the batteries can take.

 

[rgarside]

The Adverc unit is not claimed to be as clever as the Sterling ones, but it seems to do a reasonable job of giving a higher voltage for bulk charging, then dropping to a float level.

 

[pvb]

So if you do use a Sterling Alternator to battery charger beware of the potential problems. It works by making the alternator work flat out to produce a high current and low voltage. This makes it overheat, so it's effective power output falls away very quickly. If the engine is already old then this treatment may kill the alternator quickly. It would be better, and cheaper, to get the alternator modified to accept an external regulator with sensors to detect the alternator temperature and the batteries temperature.

It's worth noting that the Sterling Alt-to-Bat charger is supplied with both alternator and battery temperature sensors.

 

[ytd]

We have a 2004 year volvo 110A alternator feeding 2x200Ah AGM batteries plus a 60Ah flooded starter battery through a Nextstep smart regulator. The house batteries were changed to AGM about 3 years ago and are performing much better than the flooded ones they replaced. As I understand it, the regulator sends all output to the start battery until it reaches a set voltage and then parallels it with the house batteries. All three then get whatever the alternator produces until the temperature probe on one of the house batteries tells the alternator to slow down a bit. The voltage during this phase starts about 13v but increases to 15v as the batteries charge. When the batteries are fully charged, which usually takes many hours since we are on a swing mooring and have no solar panels, the regulator switches to a float voltage of 13.8v. The regulator manual had instructions for setting its dip switches from flooded to AGM but when I looked at them it seemed ours were already set to AGM. We have no alternator temperature sensor but when charging hard on a hot day it is too hot to touch. The standard belt on our alternator is not really up to the job and needs to be replaced annually. When the alternator is charging hard you can smell hot rubber. I reckon the OP should go ahead with the AGMs. They seem to charge quicker and hold more charge than the flooded ones they replaced. They were also appreciably heavier. So much so that we beefed up the battery hold downs as we doubted the standard ones would hold the weight in the event of a rollover.