mikevye Posted July 18, 2013 Report Share Posted July 18, 2013 Is it a reasonable suggestion to supplement the existing alternator/ battery charging with additional input from an external battery charger supplied from my dometic alternator or would they balance each other out and I end up with the same charging rate? Engine Barrus 45 with 3 alternators and smartbank split charge system installed. Link to comment Share on other sites More sharing options...
Chris Pink Posted July 18, 2013 Report Share Posted July 18, 2013 There would be little point in using the two together. All that would happen would you'd reach the end of the bulk stage quicker and absorbtion would be slower and not use any extra power. Link to comment Share on other sites More sharing options...
bizzard Posted July 18, 2013 Report Share Posted July 18, 2013 See my latest Topic in living afloat old bean. Link to comment Share on other sites More sharing options...
nicknorman Posted July 18, 2013 Report Share Posted July 18, 2013 (edited) If you have a charger on board it allows you to charge if something fails in the normal charging system(alternator) and, depending on the charger, may allow you increase the voltage from time to time for an equalise charge. Otherwise I agree with Chris, it won't end up charging your batteries significantly quicker if you use the sources of charge all at the same time - well, unless the battery bank is very large and/ or the alternators are very small. Edited July 18, 2013 by nicknorman Link to comment Share on other sites More sharing options...
by'eck Posted July 18, 2013 Report Share Posted July 18, 2013 Is it a reasonable suggestion to supplement the existing alternator/ battery charging with additional input from an external battery charger supplied from my dometic alternator or would they balance each other out and I end up with the same charging rate? Engine Barrus 45 with 3 alternators and smartbank split charge system installed. Not sure how you intend to power a battery charger from your domestic battery alternator but in any case need a bit more info to answer your question comprehensively: Output of each of your three alternators? Number and size of batteries/banks? What heavy loads you put on your main service bank? - inverter supplying washing machine for example. There is a limit to how much current you can squeeze into a battery bank at any particular point in the charge cycle, above which charge times won't be significantly reduced, as suggested above. However if you intend to run say a washing machine from batteries via inverter then extra current from the alternators will always help. Redundancy by using at least two of your three alternators to supply the main service bank ought to be sort as well in case one goes down. Link to comment Share on other sites More sharing options...
nicknorman Posted July 18, 2013 Report Share Posted July 18, 2013 Not sure how you intend to power a battery charger from your domestic battery alternator but in any case need a bit more info to answer your question comprehensively: Output of each of your three alternators? Number and size of batteries/banks? What heavy loads you put on your main service bank? - inverter supplying washing machine for example. There is a limit to how much current you can squeeze into a battery bank at any particular point in the charge cycle, above which charge times won't be significantly reduced, as suggested above. However if you intend to run say a washing machine from batteries via inverter then extra current from the alternators will always help. Redundancy by using at least two of your three alternators to supply the main service bank ought to be sort as well in case one goes down. I had presumed that when he said 3 alternators, one was a TravelPower but I could be wrong! Link to comment Share on other sites More sharing options...
by'eck Posted July 18, 2013 Report Share Posted July 18, 2013 (edited) I had presumed that when he said 3 alternators, one was a TravelPower but I could be wrong! Yes that makes sense although the OP did mention powering a (mains?) battery charger from the domestic alternator. If that's the case then such a charger would allow extra charge current if and when its was needed. I believe you use yours in a similar manner Nick. ETA: ho hum - just re-read Dometic Edited July 18, 2013 by by'eck Link to comment Share on other sites More sharing options...
nicknorman Posted July 18, 2013 Report Share Posted July 18, 2013 Yes that makes sense although the OP did mention powering a (mains?) battery charger from the domestic alternator. If that's the case then such a charger would allow extra charge current if and when its was needed. I believe you use yours in a similar manner Nick. ETA: ho hum - just re-read Dometic Oh yes, I missed the missing "s" as well! If we put the TravelPower on, it automatically feeds the Mastervolt Combi so can charge the batteries, however whether any current flows depends on the Combi voltage settings and battery temperature. I think that the 175A main alternator is plenty for a 440AH bank so don't try to force more in. What I sometimes do is to increase the Combi voltage near the end of the charge to do a bit of an equalisation over-charge - the batteries seem to like that! Link to comment Share on other sites More sharing options...
bowten Posted July 18, 2013 Report Share Posted July 18, 2013 Is it a reasonable suggestion to supplement the existing alternator/ battery charging with additional input from an external battery charger supplied from my dometic alternator or would they balance each other out and I end up with the same charging rate? Engine Barrus 45 with 3 alternators and smartbank split charge system installed. I have 450 amp Trojan battery bank with 175amp alternator and 3.5kva travel power.I have recently stopped using the 175amp alternator and just use the T/P through a Victron charger which is a 1600/70/12.I find the batteries will be more cared for in this setup rather than using the alternator and the charger together. Link to comment Share on other sites More sharing options...
nicknorman Posted July 18, 2013 Report Share Posted July 18, 2013 I have 450 amp Trojan battery bank with 175amp alternator and 3.5kva travel power.I have recently stopped using the 175amp alternator and just use the T/P through a Victron charger which is a 1600/70/12.I find the batteries will be more cared for in this setup rather than using the alternator and the charger together. You have therefore reduced your maximum charging current from 175A to 70A. How do you find the time taken to fully recharge compares pre- and post- this change? Link to comment Share on other sites More sharing options...
Arthur Brown Posted July 18, 2013 Report Share Posted July 18, 2013 Lots depends on the life style that you live. If you cruise for 6 engine hours a day then you may need little to supplement this, If you moor til the batteries are flat then big solar is a good answer. I would always have a selection of charge methods, including charger from shoreline and maybe a petrol genset for emergency use. Also the start battery could have a SMALL solar panel regardless Link to comment Share on other sites More sharing options...
bottle Posted July 18, 2013 Report Share Posted July 18, 2013 You have therefore reduced your maximum charging current from 175A to 70A. How do you find the time taken to fully recharge compares pre- and post- this change? I have found that charging the batteries from the multi, supplied by the standalone generator is more effective/quicker than using the engine alternator. Alternator is 24v, 80 amp. multi is 24v 50 amp charger. Alternator charges at 28.8v, multi charger at 29.2v (temperature compensated) Link to comment Share on other sites More sharing options...
mikevye Posted July 19, 2013 Author Report Share Posted July 19, 2013 Many thanks for your responses troops, still no wiser as to an authoritive decision, where's Gibbo when you need him? Link to comment Share on other sites More sharing options...
bottle Posted July 19, 2013 Report Share Posted July 19, 2013 Mike Not authoritative in any way but my understanding and it may be wrong, is that when charging from two sources if not matched (voltage output ?) one of them will shut down. There you are clear as mud. Link to comment Share on other sites More sharing options...
by'eck Posted July 19, 2013 Report Share Posted July 19, 2013 Mike Not authoritative in any way but my understanding and it may be wrong, is that when charging from two sources if not matched (voltage output ?) one of them will shut down. There you are clear as mud. Maybe not shut down but go into idle, and then only when the max charge voltage of the source with the lowest setting is achieved. Link to comment Share on other sites More sharing options...
bottle Posted July 19, 2013 Report Share Posted July 19, 2013 By'eck I was nearly right. Link to comment Share on other sites More sharing options...
nicknorman Posted July 19, 2013 Report Share Posted July 19, 2013 (edited) Maybe not shut down but go into idle, and then only when the max charge voltage of the source with the lowest setting is achieved. Yes, and the regulation is fairly "soft" so that in absorption, as the voltage of the charger is adjusted (if your charger allows that) the proportion of current being supplied by the alternator vs the charger changes over a relatively wide range of voltages - in other words it doesn't suddenly flip from being supplied by the alternator, to the charger, or vice versa. Back to OP's point, it depends on the power of the 12v alternators. Presuming they are fairly large, especially in combination, I don't think adding the charger output will make any difference to the charging time, because the batteries won't be able to absorb the extra current available quickly enough. Its likely to come out of bulk almost immediately. But as I mentioned, the ability to be able to do an equalise charge is a useful one, and a charger gives you more redundancy of supply. Edited July 19, 2013 by nicknorman Link to comment Share on other sites More sharing options...
Richard10002 Posted July 20, 2013 Report Share Posted July 20, 2013 Is it a reasonable suggestion to supplement the existing alternator/ battery charging with additional input from an external battery charger supplied from my dometic alternator or would they balance each other out and I end up with the same charging rate? Engine Barrus 45 with 3 alternators and smartbank split charge system installed. If you fit a simple ammeter for a few quid, or even a monitor like a NASA BM 1 or 2, for a hundred quid or so, you would be able to see the differences at different points in the charging process. Link to comment Share on other sites More sharing options...
mikevye Posted July 20, 2013 Author Report Share Posted July 20, 2013 Mike Not authoritative in any way but my understanding and it may be wrong, is that when charging from two sources if not matched (voltage output ?) one of them will shut down. There you are clear as mud. Maybe not shut down but go into idle, and then only when the max charge voltage of the source with the lowest setting is achieved. I thought this would be the case I just wanted to here the news from more knowledgeable source(s). Looks like battery charger on its own via my Honda then. Unless someone advises differently? Many thanks Mike Link to comment Share on other sites More sharing options...
smileypete Posted July 20, 2013 Report Share Posted July 20, 2013 (edited) Travelpower and £££ batt charger may be a bit more efficient than 12V alt. If the engine room gets hot and the alts much hotter that may be a consideration too. cheers, Pete. ~smpt~ Edited July 20, 2013 by smileypete Link to comment Share on other sites More sharing options...
bowten Posted July 21, 2013 Report Share Posted July 21, 2013 You have therefore reduced your maximum charging current from 175A to 70A. How do you find the time taken to fully recharge compares pre- and post- this change? I haven't used the 175 amp alt with these batteries(Trojan 6v) only the T/P and Victron Charger.I am not sure I want such to use the 175 amp alt on these batteries because I am sure it killed my previous leisure batteries.I think by using the mains charger the Trojans will be better cared for even if I am using slightly more fuel to do so. Link to comment Share on other sites More sharing options...
nicknorman Posted July 21, 2013 Report Share Posted July 21, 2013 I haven't used the 175 amp alt with these batteries(Trojan 6v) only the T/P and Victron Charger.I am not sure I want such to use the 175 amp alt on these batteries because I am sure it killed my previous leisure batteries.I think by using the mains charger the Trojans will be better cared for even if I am using slightly more fuel to do so. Interesting - you mean killed them because the current was too high, or because of something to do with the voltage? Link to comment Share on other sites More sharing options...
nb Innisfree Posted July 21, 2013 Report Share Posted July 21, 2013 (edited) With the 1% charging rule a battery can safely take a charging amperage of 1amp for each 1% of its depth of discharge (DoD) i.e. with a 200ah batt =100 amps can go into it @ 50% DoD, 80amps@ 40% DoD etc. At acceptance voltage (approx 80% SoC) battery will dictate the amount. So with a 175amp charger, any less than 875ah of battery will, in theory, run a risk of exceeding this rule when in bulk charge. In practice we hammer our batts nuts off. Edited July 21, 2013 by nb Innisfree Link to comment Share on other sites More sharing options...
nicknorman Posted July 21, 2013 Report Share Posted July 21, 2013 With the 1% charging rule a battery can safely take a charging amperage of 1amp for each 1% of its depth of discharge (DoD) i.e. with a 200ah batt =100 amps can go into it @ 50% DoD, 80amps@ 40% DoD etc. At acceptance voltage (approx 80% SoC) battery will dictate the amount. So with a 175amp charger, any less than 875ah of battery will, in theory, run a risk of exceeding this rule when in bulk charge. In practice we hammer our batts nuts off. We've got 440Ah, so at 50% that's 220A according to your formula. In practice I find that initial 175A current starts to reduce fairly quickly (ie bulk phase ends pretty quickly) so not convinced we are exceeding your rule of thumb limit. In any case, there is a bit of a compromise to be had between maximising battery longevity and not consuming more fuel than necessary,if you have to run the engine just to charge the batteries. People do talk about a 20 or 25% charger to battery capacity ratio which we obviously exceed, but I haven't found any hard data that shows how much more rapidly life is consumed by fast charging. Link to comment Share on other sites More sharing options...
nb Innisfree Posted July 21, 2013 Report Share Posted July 21, 2013 We've got 440Ah, so at 50% that's 220A according to your formula. In practice I find that initial 175A current starts to reduce fairly quickly (ie bulk phase ends pretty quickly) so not convinced we are exceeding your rule of thumb limit. In any case, there is a bit of a compromise to be had between maximising battery longevity and not consuming more fuel than necessary,if you have to run the engine just to charge the batteries. People do talk about a 20 or 25% charger to battery capacity ratio which we obviously exceed, but I haven't found any hard data that shows how much more rapidly life is consumed by fast charging. Yes I agree, theory and practicality and all that. Also we are talking about batt capacity when new, we have 480 ah @24v but possibly down to half that now, so we have 100 amps going into 240ah and we have survived so far! When our batts were new we would sometimes be in bulk charge and at full output for an hour or so if batts were well discharged. Just to add, it's not my theory but taken from Gibbo's Smartgauge site. Link to comment Share on other sites More sharing options...
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