Alternator output

[voyager35]

Hi I have a twin engine cat with a 120amp alternator on each engine. the boat has a Victron lithium battery installation with the lithium batteries being charged by two 30amp battery to battery charges (giving a total output of 60 amp). The system is installed so it charges from either engine or both.
When both engines are running above about 1400 rpm I am getting around 55 amps going into the lithium batteries. however when only one engine is on even at higher rpm where the alternator should be producing maximum output I only see around 45 amp charge.
Is there a reason for this . also if i add a third 30 amp BtoB charger would i get more output when running on one engine.

 

[Refueler]

The bit you have left out ... at what state of charge are you seeing this 55A (both) 45A (one engine) ??

As batterys charge up - amp rate falls dramatically in the higher charged area. Just because an alternator is rated at 120A - does not mean you will get 120A ... it all depends on what battery state is etc.

As to your general other .... I leave that to others to answer.

 

[voyager35]

With lithium batteries the rate of charge only tappers of when they are virtually full ie. showing 99/100% on the display

 

[Refueler]

With lithium batteries the rate of charge only tappers of when they are virtually full ie. showing 99/100% on the display

I only have about 100 Lithiums of various chemistrys from small to large - I use ..... what would I know ? With Programmable Chargers that display real time data ... and I can also record to PC ...

If your charger is still banging in high amps at 99 - 100% .... I don't want to be anywhere in that locality thank you.

 

[voyager35]

I only have about 100 Lithiums of various chemistrys from small to large - I use ..... what would I know ? With Programmable Chargers that display real time data ... and I can also record to PC ...

If your charger is still banging in high amps at 99 - 100% .... I don't want to be anywhere in that locality thank you.

That's interesting, the installed system is all Victron including the monitoring and charging rates. I have suspected that when it shows 100% charged on the display that this is an indicated value and that there is probably some more capacity in the batteries as the charge rate quickly tapers off but is still higher than the background power draw into the boats systems.
i am seeing this rate of charge until the battery charge % is past 95% but i cant say I have monored it that closely. It doesnt seem to make any difference to the charge rate if the batteries are at 60% or 90%

 

[[2574]]

If you’re using an ah counter to represent battery charge status then be very wary of what you might see on the monitor; they’re very inaccurate indeed. I’ve an all Victron system and the shunt reports 100% charge status after a set period at a set voltage but frankly it’s nonsense. If your charging system is still inputting high A when the Victron monitor says 100% then very likely your batteries are nowhere near 100%.

 

[Slipstream 34]

Alternator output depends on rpm. The stated output, in your case 120 amps, is at max revs. With a modest 1400 rpm 45 amps may well be what the alternators are producing. I have a 90amp alternator and a 30/60 amp b2b charger. Below 1600rpm the alternator cannot keep up with the b2b charger at 60amps. If you can monitor the starter battery voltage have a look at it at different rpms. It is a good indication of what your alternators are outputting, if the starter battery voltage dips then the alternator is struggling to match the demands.

 

[geem]

I only have about 100 Lithiums of various chemistrys from small to large - I use ..... what would I know ? With Programmable Chargers that display real time data ... and I can also record to PC ...

If your charger is still banging in high amps at 99 - 100% .... I don't want to be anywhere in that locality thank you.

It depends what you programme as 100% on the victron system. 100% victron can be 90% actual lithium SOC. Thr Victron kit can be set like this so you are keeping away from the high stress charging area of lithium batteries for longer life. Its quite normal procedure for lithium domestic batteries on a boat

 

[geem]

Alternator output depends on rpm. The stated output, in your case 120 amps, is at max revs. With a modest 1400 rpm 45 amps may well be what the alternators are producing. I have a 90amp alternator and a 30/60 amp b2b charger. Below 1600rpm the alternator cannot keep up with the b2b charger at 60amps. If you can monitor the starter battery voltage have a look at it at different rpms. It is a good indication of what your alternators are outputting, if the starter battery voltage dips then the alternator is struggling to match the demands.
View attachment 157970

Also bear in mind thatt when the B2B gets hot it's output drops dramatically

 

[kwb78]

Also bear in mind thatt when the B2B gets hot it's output drops dramatically

The Victron chargers are very temperature dependent. The 30A Orion is rated at 430W output at 25°C, but that drops to 360W at 40°C, and it drops a further 3% for each °C above 40°C. If they are mounted in an engine bay, the ambient temperature could have a significant effect, and it could be well worth installing a fan to cool them or moving them if charging speed is important.

 

[William_H]

Note the above graph refers to "alternator RPM" which is dependent on pulley size ratios for a given engine RPM. May be ratios could be improved to get increase alternator RPM. Alternator rated output current would be under ideal conditions of temperature and RPM. (selling hype). Perhaps OP should not worry about alternator output. ol'will

 

[Refueler]

It depends what you programme as 100% on the victron system. 100% victron can be 90% actual lithium SOC. Thr Victron kit can be set like this so you are keeping away from the high stress charging area of lithium batteries for longer life. Its quite normal procedure for lithium domestic batteries on a boat

Ok ... that's re-assuring as casual attitude to batterys particularly Li based .. but also Lead Acid - can have dire results.

Its not uncommon for Li users to set OEM chargers to default out at 0.1v per cell below full charged V ...

This also as many know happens with Lead Acid anyway ... without 3rd party intervention in charging ... charging usually only gets into the high 90's % ...

 

[Refueler]

Note the above graph refers to "alternator RPM" which is dependent on pulley size ratios for a given engine RPM. May be ratios could be improved to get increase alternator RPM. Alternator rated output current would be under ideal conditions of temperature and RPM. (selling hype). Perhaps OP should not worry about alternator output. ol'will

Like many things .... the specs usually quote max that is rarely attained.

Considering changing pulley ... pal of mine did just that ... he actually ended up with literally no gain at all ... as the engine was loaded more. OK - if you have a decent sized engine .. my 4-107 as example could handle an increase ... but a small 1GM or other - its going to be a load that is basically unsuited.

If OP has 120A alternators - they would be high load units - so any increase would be serious ...

 

[Refueler]

That's interesting, the installed system is all Victron including the monitoring and charging rates. I have suspected that when it shows 100% charged on the display that this is an indicated value and that there is probably some more capacity in the batteries as the charge rate quickly tapers off but is still higher than the background power draw into the boats systems.
i am seeing this rate of charge until the battery charge % is past 95% but i cant say I have monored it that closely. It doesnt seem to make any difference to the charge rate if the batteries are at 60% or 90%

According another post - the % values and set points are user set ... therefore I would assume that your V system is set at lower than actual 100% for safe charging.

Be interesting to know the relation of CA vs CV in charge of the V system .... Li usually is primaril;y designed to be charged at Constant Amps (CA) until a level is reached (level often set by user) .. then it becomes Constant Voltage (CV) with Amps tapering off significantly ... of course this would be modified by Float and Maintenance phases of a V system.

 

[Alex_Blackwood]

Hi I have a twin engine cat with a 120amp alternator on each engine. the boat has a Victron lithium battery installation with the lithium batteries being charged by two 30amp battery to battery charges (giving a total output of 60 amp). The system is installed so it charges from either engine or both.
When both engines are running above about 1400 rpm I am getting around 55 amps going into the lithium batteries. however when only one engine is on even at higher rpm where the alternator should be producing maximum output I only see around 45 amp charge.
Is there a reason for this . also if i add a third 30 amp BtoB charger would i get more output when running on one engine.

Very simply and without all the technical blurb, two are more efficient than one! might be worth measuring the difference in charging voltage with two as opposed to one! When you go from two to one the load on the single alternator and subsequently the engine increases this will result in a slight drop in output effecting current and voltage. Never mind all the clever theory, it will!
As for fitting a third B2B where is it going to be fed from, another battery or in Parallel with one of the other B2B's? either way you still have the same alternators.
You would be adding extra load to them. And possibly more drain on the batteries. Don't think you would gain anything maybe just split the charge between the three. Perhaps, as others have said, may be worth checking the Li. charging regime settings.

 

[voyager35]

The Victron chargers are very temperature dependent. The 30A Orion is rated at 430W output at 25°C, but that drops to 360W at 40°C, and it drops a further 3% for each °C above 40°C. If they are mounted in an engine bay, the ambient temperature could have a significant effect, and it could be well worth installing a fan to cool them or moving them if charging speed is important.

the btb chargers ge trealy hot 60 degrees+ so i have started using a fan on them and this drops the temp by over 20 degrees . I will check the outputs next time I run the water maker and have a lot of charging to do

 

[voyager35]

According another post - the % values and set points are user set ... therefore I would assume that your V system is set at lower than actual 100% for safe charging.

Be interesting to know the relation of CA vs CV in charge of the V system .... Li usually is primaril;y designed to be charged at Constant Amps (CA) until a level is reached (level often set by user) .. then it becomes Constant Voltage (CV) with Amps tapering off significantly ... of course this would be modified by Float and Maintenance phases of a V system.

After i had installed the system the Victron agent came out to the boat , commissioned it and set up the values. the words safe and conservative were used a lot. I do not have the expertise to mess with these

 

[voyager35]

Very simply and without all the technical blurb, two are more efficient than one! might be worth measuring the difference in charging voltage with two as opposed to one! When you go from two to one the load on the single alternator and subsequently the engine increases this will result in a slight drop in output effecting current and voltage. Never mind all the clever theory, it will!
As for fitting a third B2B where is it going to be fed from, another battery or in Parallel with one of the other B2B's? either way you still have the same alternators.
You would be adding extra load to them. And possibly more drain on the batteries. Don't think you would gain anything maybe just split the charge between the three. Perhaps, as others have said, may be worth checking the Li. charging regime settings.

When I run one engine it will charge both engine start batteries. I would therefor assume that the b2b chargers are pulling power from both

 

[Alex_Blackwood]

When I run one engine it will charge both engine start batteries. I would therefor assume that the b2b chargers are pulling power from both

Hi, I appreciate that. Also that when you run both engines similar will occur. I was in my post referring to the alternators. I am trying to be non-technical so please forgive me if I err too much in that direction. Answer to your reduced power on one alternator, that is to be expected. If you imagine that you have two water tanks being filled by two pumps (alternators). If you switch off one pump the other will not be able to fill the tanks as efficiently. If you now drain these two tanks, into another tank, with another two pumps (B2B's) the single pump, supplying the first two tanks will not maintain the level as well as two pumps would. Therefore the output will suffer. All very simplified but your single alternator may just be struggling a bit.

If you now add another pump to the outlet of the first two tanks how do you connect it? Do you connect it two both tanks, in which case they can cross feed. If you put in non return valves(Diodes) the pressure will be further reduced. Or do you just connect it as an addition to one tank which will then drain quicker than the other. It will, I suspect, if connected to both tanks share the drain equally with the other two pumps from the tanks but at reduced pressure. Will it fill the second tank any quicker? I don't think you would get any advantage. You can't get out more than you put in. In any case I suspect that the flow will be be restricted by what the third tank can accept.

All the above is very much simplified, However, I hope of some use. I have no idea of how your system is set up. Do your two alternators run in parallel or does each supply its own respective battery, when running together. How is the switching from two to one achieved. Is the system controlled by diodes, relays, switches or some combination of these three? We don't even know where the alternators are sensing from.
Is your basic charging system (Alternators and starter batteries) The origin for the boat and used to charge more traditional batteries prior to the Li fit?
There are all sorts of considerations but I suspect that you may have something of a compromise system with the new and original fits.
As I said earlier is there any difference in the starter battery charging voltages, measured at the terminals, between both alternators on and only one. I suspect that it may be lower with just one. Who knows??? Worth checking both batteries.
Possibly more questions than answers.

 

[voyager35]

Hi, I appreciate that. Also that when you run both engines similar will occur. I was in my post referring to the alternators. I am trying to be non-technical so please forgive me if I err too much in that direction. Answer to your reduced power on one alternator, that is to be expected. If you imagine that you have two water tanks being filled by two pumps (alternators). If you switch off one pump the other will not be able to fill the tanks as efficiently. If you now drain these two tanks, into another tank, with another two pumps (B2B's) the single pump, supplying the first two tanks will not maintain the level as well as two pumps would. Therefore the output will suffer. All very simplified but your single alternator may just be struggling a bit.

If you now add another pump to the outlet of the first two tanks how do you connect it? Do you connect it two both tanks, in which case they can cross feed. If you put in non return valves(Diodes) the pressure will be further reduced. Or do you just connect it as an addition to one tank which will then drain quicker than the other. It will, I suspect, if connected to both tanks share the drain equally with the other two pumps from the tanks but at reduced pressure. Will it fill the second tank any quicker? I don't think you would get any advantage. You can't get out more than you put in. In any case I suspect that the flow will be be restricted by what the third tank can accept.

All the above is very much simplified, However, I hope of some use. I have no idea of how your system is set up. Do your two alternators run in parallel or does each supply its own respective battery, when running together. How is the switching from two to one achieved. Is the system controlled by diodes, relays, switches or some combination of these three? We don't even know where the alternators are sensing from.
Is your basic charging system (Alternators and starter batteries) The origin for the boat and used to charge more traditional batteries prior to the Li fit?
There are all sorts of considerations but I suspect that you may have something of a compromise system with the new and original fits.
As I said earlier is there any difference in the starter battery charging voltages, measured at the terminals, between both alternators on and only one. I suspect that it may be lower with just one. Who knows??? Worth checking both batteries.
Possibly more questions than answers.

Thank you, yes each alternator is charging a lead acid start battery which are connected together by a Victron cirex switch that appears to open and connect the two start battery's together when one is above a certain voltage ie alternator charging
I will test the alternator outputs and see what we are getting