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18 minutes ago, Tony Brooks said:

I wish you would also stop going on about DC to DC converters because they are not what you are asking about. A DC to DC converter on its own simply converts one DC voltage to another so, for an example, can run a 12V car radio in a 24v truck. You are talking about a battery to battery charger that contains as DC to DC converter an much more control electronics.

 

Which was my interpretation of the original question and hence my response in post #2

 

Unfortunately a poorly crafted question will often result in what the OP sees as 'the wrong answers' or 'being patronised'. There is a skill in asking the correct question.

 

There is an old saying that is very true "what I wrote, what you thought I wrote and what I actually meant to write can be very different."

Edited by Alan de Enfield
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Infinite output alternators do not exist in the real world and boating is a real world activity.

Everything on a boat is a compromise.

The battery company specs are worthless to you because (as you said) charging batteries as quickly as possible can be a big factor on a boat, but is not important to other applications. Fast charging and maximum lifetime are a conflicting compromise and only you can choose your position on this compromise.

 

An alternator plus controller IS a variable output DC generator so an additional DC DC converter is just not required.

 

Us liveaboard boaters have long since solved your problem, or at least 99% of it. An alternator plus controller set to about 14.8 volts (for Trojans) plus an occasional equalisation gives an almost perfect compromise between fast charging and battery life expectancy. A means to manually adjust the charge voltage is even better but this needs to be done by a human, it can not be automated.

 

................Dave

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3 hours ago, Peanut34 said:

Right, I'll see if I can give it another steer, although I really don't think forums are for me.

You could be right and, as you seem to know it all, what use do you have for them?

3 hours ago, Peanut34 said:

 

Let's keep it theoretical: It's Wednesday 23rd December 2020, I have an infinite output alternator, three 12 V flooded batteries totalling 300 Ah, and a lot more money than sense.

Your manner doesnt do you any favours :( 

3 hours ago, Peanut34 said:

 

Bulk is straightforward, but if I regulate to a single bulk voltage and the temperature of the batteries changes, I've fallen off the tightrope, I'm now sub-maximal, and I've failed in my objectives, right?

Your manner doesnt do you any favours, right?

3 hours ago, Peanut34 said:

Quick (and yes, poor) post: Does anyone have one of these?

Yes... I've got one :)

3 hours ago, Peanut34 said:

Ah well. As I said, I don't think forums are for me.

So true you said it twice :( 

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4 hours ago, Peanut34 said:

snip

 

Bulk is straightforward, but if I regulate to a single bulk voltage and the temperature of the batteries changes, I've fallen off the tightrope, I'm now sub-maximal, and I've failed in my objectives, right?

 

snip

 

No wrong. If you are controlling the charging voltage by an active control system rather than the inductance designed into charging device you will not e in bulk, you will be in acceptance.

 

The voltage during bulk charging is not, as far as I know, normally regulated. The bulk voltage is depressed because of the high current and the inductance it produces but its not actively regulated. Basically voltage in bulk will always be lower than during acceptance so you can't do  much about it. I agree if you changed bulk to acceptance btu even then have you made any formal or informal estimates of the difference to the overall charging time and battery life temperature compensation will actually make and its cost effectiveness?

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11 minutes ago, Tony Brooks said:

 

No wrong. If you are controlling the charging voltage by an active control system rather than the inductance designed into charging device you will not e in bulk, you will be in acceptance.

 

The voltage during bulk charging is not, as far as I know, normally regulated. The bulk voltage is depressed because of the high current and the inductance it produces but its not actively regulated. Basically voltage in bulk will always be lower than during acceptance so you can't do  much about it. I agree if you changed bulk to acceptance btu even then have you made any formal or informal estimates of the difference to the overall charging time and battery life temperature compensation will actually make and its cost effectiveness?

There are some controllers that do allow the bulk voltage to be adjusted but I really don't understand this, bulk charging is a constant current process so bulk voltage is controlled only by alternator performance (and engine speed). I can only assume they mean the voltage at which the bulk phase is deemed to have completed.

 

I am starting to think that the OP is a troll. Wouldn't it be great if Gibbo had come back to take his revenge on the forum. ?

 

................Dave

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11 minutes ago, dmr said:

There are some controllers that do allow the bulk voltage to be adjusted but I really don't understand this, bulk charging is a constant current process so bulk voltage is controlled only by alternator performance (and engine speed). I can only assume they mean the voltage at which the bulk phase is deemed to have completed.

 

I am starting to think that the OP is a troll. Wouldn't it be great if Gibbo had come back to take his revenge on the forum. ?

 

................Dave

Yes our Mastervolt Combi has charger settings for bulk, absorb and float voltages. Generally the bulk voltage is set higher than the absorb voltage. I think the point is, as you say, that the system switches from bulk to absorb once the bulk voltage is achieved (and held for a specified duration). Then it backs off to absorb voltage which is perhaps a little kinder to the batteries.

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2 minutes ago, nicknorman said:

Yes our Mastervolt Combi has charger settings for bulk, absorb and float voltages. Generally the bulk voltage is set higher than the absorb voltage. I think the point is, as you say, that the system switches from bulk to absorb once the bulk voltage is achieved (and held for a specified duration). Then it backs off to absorb voltage which is perhaps a little kinder to the batteries.

Yes, I think one of my Victron things does the same, but I can't confirm as I can only talk to the charger when the engine is running and its not (my lovely Trojans mean that even in winter we only need to do an engine run every other day ?)

 

But I still don't fully understand why a separate "end of bulk" voltage is needed, will the bulk phase getting up to specified absorption voltage not achieve the same?  Maybe it relates to chargers were the duration of the bulk phase is used to estimate other charging parameters?

 

I have a new project to add to my list of interesting things that I never quite get round to doing. I suspect that external alternator diodes would reduce alternator heat significantly (I have read that 50% of heat is from the diodes) and so allow the alternator to get closer to its rated current. There is a slightly naff fan cooled device available but a narrowboat is not far off an infinite heatsink so a fanless device bolted to the engine bed should be fine.

 

..............Dave

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4 minutes ago, dmr said: 

But I still don't fully understand why a separate "end of bulk" voltage is needed, will the bulk phase getting up to specified absorption voltage not achieve the same?  Maybe it relates to chargers were the duration of the bulk phase is used to estimate other charging parameters?

Thinking about it, I guess it may come back to the issue I was describing in the sketches I posted earlier. Having a higher bulk voltage means that as the soft analogue regulation approaches the nominal absorb voltage, the current is going to have dropped off significantly. By specifying a higher bulk voltage, that current drop off for a specific instantaneous voltage in the  bulk phase, is less. Then it switches to absorb to avoid too much voltage for prolonged periods. I suppose it is almost like a 1-step I term in a PID control loop.

 

What I notice with my own regulator, which has very precise and “hard” regulation, is that max current can be sent to the batteries until about 0.1v from the regulated voltage. This might seem a good thing but I am fairly sure it’s not particularly good for the LA batteries. But anyway, it means that only 1 regulated voltage setting is needed. I have only built in a float mode for when I switch to Li batteries.

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59 minutes ago, Tony Brooks said:

 

have you made any formal or informal estimates of the difference to the overall charging time and battery life temperature compensation will actually make and its cost effectiveness?

No, but it sounds exciting, doesn't it....depending on how you define exciting.

 

I think the impact on battery life is almost impossible to quantify without a very lengthy practical exercise, but charging time could be done. And interesting because if you regulated at a single, safe voltage to avoid gassing in summer, you'd be undercharging all winter, wouldn't you? [Actual question, not a statement]

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8 minutes ago, Peanut34 said:

No, but it sounds exciting, doesn't it....depending on how you define exciting.

 

I think the impact on battery life is almost impossible to quantify without a very lengthy practical exercise, but charging time could be done. And interesting because if you regulated at a single, safe voltage to avoid gassing in summer, you'd be undercharging all winter, wouldn't you? [Actual question, not a statement]

Yes that is why proper marine battery chargers, Combis, add-on alternator controllers etc have a battery temperature sensor which is used to adjust charging voltage.

Edited by nicknorman
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26 minutes ago, Peanut34 said:

No, but it sounds exciting, doesn't it....depending on how you define exciting.

 

I think the impact on battery life is almost impossible to quantify without a very lengthy practical exercise, but charging time could be done. And interesting because if you regulated at a single, safe voltage to avoid gassing in summer, you'd be undercharging all winter, wouldn't you? [Actual question, not a statement]

No, I disagree with both. If you mean in winter you could safely charge at a slightly higher voltage then yes. That far I agree with but you say undercharging. If we take under charging to mean never reaching all but fully charged then no, you are wrong because getting to fully charged at any given voltage has a time component  so in winter you would need to charge for (slightly?) longer, that is all. As long as the voltage was above about 13.6 the batteries would be fully charged eventually but it would take days and days and no doubt there would be a degree of extra sulphation. Once we get to 14.4V + things would fully recharge a lot faster.

 

I agree about battery life but I think we collectively have enough experience to say that fully charging as frequently and often as possible and keeping the discharge to an acceptable level (we tend to say no deeper than 50%) will make a greater difference to battery longevity than wringing the last few 0.1s of a volt of extra voltage out of the charge source.  At a guess we are probably talking about maybe an hour or so over a 10 to 12 hour charge which is not a lot once a week in my view and not worth spending much money on.

 

Just because  a charge source specifies something they call bulk charge voltage unless you test it and prove it really is the bulk voltage I think it means something else like "maximum bulk voltage" or the voltage at which the charge source will start  regulating and doing its time calculations on.

Edited by Tony Brooks
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24 minutes ago, Peanut34 said:

No, but it sounds exciting, doesn't it....depending on how you define exciting.

 

I think the impact on battery life is almost impossible to quantify without a very lengthy practical exercise, but charging time could be done. And interesting because if you regulated at a single, safe voltage to avoid gassing in summer, you'd be undercharging all winter, wouldn't you? [Actual question, not a statement]

Sulphation from undercharging likely kills more boat batteries than anything else (including a bit of over charging) but I suspect is not a factor when the manufacturers produce their charging specification.

For many boaters sulphation is much more likely to occur in winter so temperature compensation is a very good thing because, as you suggest, undercharging in winter is a bad thing.  In addition to the automatic temperature compensation I usually make my own additional adjustment, if its summer and we intend to move almost every day I maybe bring the charge voltage down to 14.6 or 14.4. In winter I sometimes increase it to 15, though more recently tend to leave it at 14.8.

 

..............Dave

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47 minutes ago, nicknorman said:

Thinking about it, I guess it may come back to the issue I was describing in the sketches I posted earlier. Having a higher bulk voltage means that as the soft analogue regulation approaches the nominal absorb voltage, the current is going to have dropped off significantly. By specifying a higher bulk voltage, that current drop off for a specific instantaneous voltage in the  bulk phase, is less. Then it switches to absorb to avoid too much voltage for prolonged periods. I suppose it is almost like a 1-step I term in a PID control loop.

 

What I notice with my own regulator, which has very precise and “hard” regulation, is that max current can be sent to the batteries until about 0.1v from the regulated voltage. This might seem a good thing but I am fairly sure it’s not particularly good for the LA batteries. But anyway, it means that only 1 regulated voltage setting is needed. I have only built in a float mode for when I switch to Li batteries.

The Adverc does much much better than the standard regulator but I suspect its not as tight as your clever IC device. I regard keeping the voltage and current high till the very end of the bulk phase as a very big positive when charging from the engine. I expect all charging has some impact on battery life but I don't worry about this one, I suspect the saving in diesel more than outweighs any reduction in battery life. I also start my equalisations well before the charge is down to 3%. Some of our Trojans are now over 5 and a half years old and appear to be still fine so I don't think hard charging is a big issue.

 

..............Dave

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21 hours ago, Tony Brooks said:

No, I disagree with both. If you mean in winter you could safely charge at a slightly higher voltage then yes. That far I agree with but you say undercharging. If we take under charging to mean never reaching all but fully charged then no, you are wrong because getting to fully charged at any given voltage has a time component  so in winter you would need to charge for (slightly?) longer, that is all. As long as the voltage was above about 13.6 the batteries would be fully charged eventually but it would take days and days and no doubt there would be a degree of extra sulphation. Once we get to 14.4V + things would fully recharge a lot faster.

 

I agree about battery life but I think we collectively have enough experience to say that fully charging as frequently and often as possible and keeping the discharge to an acceptable level (we tend to say no deeper than 50%) will make a greater difference to battery longevity than wringing the last few 0.1s of a volt of extra voltage out of the charge source.  At a guess we are probably talking about maybe an hour or so over a 10 to 12 hour charge which is not a lot once a week in my view and not worth spending much money on.

 

Just because  a charge source specifies something they call bulk charge voltage unless you test it and prove it really is the bulk voltage I think it means something else like "maximum bulk voltage" or the voltage at which the charge source will start  regulating and doing its time calculations on.

 

I had career spanning over 40 years working with batteries, covering maintenance, installation, specification and project management.

 

Tony is absolutely spot on that the fastest battery killers are failing to fully recharge and over discharging.

 

After those two, high temperatures will significantly reduce battery life. VRSLAs (aka AGMs) life expectancy is reduced by half for every 8°C over 20°C, slighly less for wet cells, which is why in most critical applications batteries are kept in dedicated air conditioned battery rooms.

Edited by cuthound
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1 minute ago, Tony Brooks said:

and following on from that one could suggest that upping the acceptance voltage to the maximum (heating effect) will reduce the battery life as will excessive use of equalisation.

 

Absolutely, I have seen the results of batteries going into thermal runaway where people have tried to force high currents into batteries in the later stages of charge by increasing the charge voltage. Not a pretty sight.

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11 minutes ago, cuthound said:

After those two, high temperatures will significantly reduce battery life. VRSLAs (aka AGMs) life expectancy is reduced by half for every 8°C over 20°C, slighly less for wet cells, which is why in most critical applications batteries are kept in dedicated air conditioned battery rooms.

 

I didn't know that, but it's interesting.  Are those lifetime reduction figures for continuous temperatures? 

 

I'm wondering how much damage they take when they are usually <15°C but get up to 30°C or 40°C - such as batteries that sit in a boat engine bay ...

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8 minutes ago, Alan de Enfield said:

But you cannot convince a confirmed 'doubter'.

or someone who it seem has not yet realised manufacturers and marketeers spend a lot of time getting as close to lying as they can in their own rather than a customer's best interest.

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1 minute ago, Tony Brooks said:

or someone who it seem has not yet realised manufacturers and marketeers spend a lot of time getting as close to lying as they can in their own rather than a customer's best interest.

 

You do realise I am an 'MCIM' (Member of the Chartered institute of Marketing) and my Post Graduate Degree was in Marketing ?

 

Having said that - you are 'not far off' (and I have a certificate that says I'm allowed to do it).

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30 minutes ago, Alan de Enfield said:

 

You do realise I am an 'MCIM' (Member of the Chartered institute of Marketing) and my Post Graduate Degree was in Marketing ?

 

Having said that - you are 'not far off' (and I have a certificate that says I'm allowed to do it).

A degree in Bullsh!t! well I never......

Edited by gazza
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27 minutes ago, TheBiscuits said:

 

I didn't know that, but it's interesting.  Are those lifetime reduction figures for continuous temperatures? 

 

I'm wondering how much damage they take when they are usually <15°C but get up to 30°C or 40°C - such as batteries that sit in a boat engine bay ...

 

Yes continuous temperatures, but a small amount of damage is done every time the tempersture goes above 20°C (even though manufacturers quote capacity at 25°C...).

 

The amount of longevity reduction will be directly proportional to the amount of time (annual percentage) spent over 20°C.

 

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