cable type

[ditchcrawler]

 

This is where the volt drop calculation can be ignored to a large degree. BT use being so momentary (most have thermal cut-out to prevent prolonged use) means that a high charge current draw during and for a few seconds after use is so short as not to worry about too much. Doing the maths as your customer did is simply over the top. I suspect if the decision had been left to yourself you would have fitted a much lesser cross-section, assuming the charge cables were just that and not carrying the full BT motor current draw.

I have not been down this route, but what happens as the bow thruster batteries die and as the bow thruster is used its drawing current from the service batteries at the back. Surly to do a proper job you need to disconnect the charge line while the thruster is in use.

I have not been down this route, but what happens as the bow thruster batteries die and as the bow thruster is used its drawing current from the service batteries at the back. Surly to do a proper job you need to disconnect the charge line while the thruster is in use.

Even if you drop 2 volts with the high charge current it wont matter much, because as the batteries start to charge (a bit slower) the current will fall, so will the volt drop until you reach the point where the charge current is in slow single figures and the voltdrop so small it can be discounted.

[nicknorman]

Is there no way I can supply a lower charge current to avoid running such large cables while engine is running.

 

Neil

Yes you can use smaller cable, it will just take longer to recharge. You do need to protect the cable with an appropriate fuse (at both ends) and the only downside of all that is that if you abuse the bow thruster by running it a lot, you will flatten the BT battery and now you are tying to run the BT via the cable, and the fuses will blow. But providing you are sensible with your BT use it won't be a problem.

[Neil Smith]

When you say smaller, how small are we talking as I need to go and get some tomorrow.

 

Cheers Neil

[by'eck]

When you say smaller, how small are we talking as I need to go and get some tomorrow.

 

Cheers Neil

 

Sorry to interupt your discussion with Nick but this is not the way you should be thinking. Try to engineer the wiring so you get as higher charge voltage as possible at the BT batteries commensurate with sensible size cables, fused at both ends. The higher charge currents will last for such a short time in normal use of BT that its simply silly to go overboard with cable cross-section and probably even more silly to limit charge current by deliberately using undersize cable. A sensible compromise needs to be reached.

 

35mm2 cable as Keith M asserted is a good starting point although with an unusually long run as you have you may need to go to 50mm2.

 

It may also be worth considering a Sterling zero-volt drop splitter. This smart device will inhibit back feed from your service batteries when a large drain is made on the BT batteries, but at other times will parallel them for normal charging. It also has a dedicated sense terminal to drive an external alternator regulator, and so avoid buying a more expensive A to B device.

Edited January 14, 2015 by by'eck

[Keith M]

Firstly 50 mm2 will give a 1.2 volt-drop at 100 amps this would be my choice I think after looking at installation

If 50 mm is to expensive I would go no lower than 35 mm

 

Secondly I would combine the 2 alternators by using 2 volt-drop free diode systems 1 and 3 out

 

I hope the above is helpful

 

Keith

This is where the volt drop calculation can be ignored to a large degree. BT use being so momentary (most have thermal cut-out to prevent prolonged use) means that a high charge current draw during and for a few seconds after use is so short as not to worry about too much. Doing the maths as your customer did is simply over the top. I suspect if the decision had been left to yourself you would have fitted a much lesser cross-section, assuming the charge cables were just that and not carrying the full BT motor current draw.

It was to charge the batteries

 

The customer is always right

 

Keith

[Neil Smith]

Would it be better to use an alt to batt charger as we won't have access to shore line very often and they would equalise my batteries and charge faster, that's if you believe all the claims, this would link ALTs as well I am told.

 

Neil

[by'eck]

Would it be better to use an alt to batt charger as we won't have access to shore line very often and they would equalise my batteries and charge faster, that's if you believe all the claims, this would link ALTs as well I am told.

 

Neil

 

You can parallel the alternators without an A to B device. The choice is yours as to whether you choose the latter or not. Advantages are that it provides a dedicated starter battery charge feed as well as the boosted main output. I chose to fit individual Sterling alternator regulators to each of mine, as it was cheaper and achieved the same. They do require a small mod to the alternators though, but both offer a float charge mode after the batteries are fully charged, which is something that is often overlooked when discussing ways of increasing alternator voltage regulation.

 

I will mention again how useful I have found the Sterling zero volt drop splitter which can be linked to the sense point of an external alternator.

 

If you PM me I will be happy to suggest the best setup IMO for your needs, batteries and charge systems.

[smileypete]

Mr Sterling beckons.

 

Often there's no cheap off-the-shelf way of doing things...

 

cheers, Pete.

~smpt~

[by'eck]

I have not been down this route, but what happens as the bow thruster batteries die and as the bow thruster is used its drawing current from the service batteries at the back. Surly to do a proper job you need to disconnect the charge line while the thruster is in use.

 

Not the issue you imagine. Even with BT batteries disconnected the volt drop on the charge cable will simply leave the alternator feeding it working flat out but clearly unable run the BT motor effectively. I had exactly this situation when the main 600 amp BT fuse blew when BT prop became temporarily fouled. In any case even if the charge system doesn't inhibit backfeed from service bank, the BT charge cable fuse will blow by design to protect cable.

[ditchcrawler]

 

Not the issue you imagine. Even with BT batteries disconnected the volt drop on the charge cable will simply leave the alternator feeding it working flat out but clearly unable run the BT motor effectively. I had exactly this situation when the main 600 amp BT fuse blew when BT prop became temporarily fouled. In any case even if the charge system doesn't inhibit backfeed from service bank, the BT charge cable fuse will blow by design to protect cable.

Hence my other suggestion that ideally the charge circuit would be automatically disconnected when the BT is operated.

[Neil Smith]

 

You can parallel the alternators without an A to B device. The choice is yours as to whether you choose the latter or not. Advantages are that it provides a dedicated starter battery charge feed as well as the boosted main output. I chose to fit individual Sterling alternator regulators to each of mine, as it was cheaper and achieved the same. They do require a small mod to the alternators though, but both offer a float charge mode after the batteries are fully charged, which is something that is often overlooked when discussing ways of increasing alternator voltage regulation.

 

I will mention again how useful I have found the Sterling zero volt drop splitter which can be linked to the sense point of an external alternator.

 

If you PM me I will be happy to suggest the best setup IMO for your needs, batteries and charge systems.

The problem there is if I mod the alts my warranty on them will be void as it is a new barrus shire, so I thought for the sake of a bit more money I could do it without touching them, they total 190 amps but being realistic will not reach that so would the 160 amp abc cope ok.

 

Neil

[by'eck]

The problem there is if I mod the alts my warranty on them will be void as it is a new barrus shire, so I thought for the sake of a bit more money I could do it without touching them, they total 190 amps but being realistic will not reach that so would the 160 amp abc cope ok.

 

Neil

 

Well you might get away with it but otherwise may impinge on the A to B warranty, especially as replacement cost would likely be greater than an alternator. I didn't even consider the alternator warranty issue when I made the choice go with DAR's on my own new boat, the decision was purely based on cost. In any case alternators are not known for unreliability. The mod BTW is simply to get a connection to one of the brushes.

 

You could have just the larger alternator feeding through the A to B to supply service and starter batteries. The smaller one with DAR fitted via a zero volt drop spllitter could feed service and BT batteries. This would still provide service battery charging redundancy in the unlikely event of either alternator failing.

 

ETA: FWIW the well proven setup on my boat is not that different from yours. The larger 160 amp alternator feeds the 550 Ah service bank directly. The smaller 90 amp one feeds starter, BT and service battery bank in that order via intelligent zero volt drop splitter. Both alternators employ the cheapest Sterling DAR's, with the smaller one connected to the splliters dedicated sense terminal. As already mentioned the 35mm2 BT charge cables don't create a volt drop issue. Since your needs and alternators are similar, I'm tempted to suggest this may suit you best.

Edited January 15, 2015 by by'eck

[smileypete]

How much current will the BT use, and how frequently will it be used and for how long?

 

Might well be better off with slightly larger BT batts and a more modest recharge rate.

 

cheers, Pete.

~smpt~

Edited January 15, 2015 by smileypete

[Neil Smith]

 

Well you might get away with it but otherwise may impinge on the A to B warranty, especially as replacement cost would likely be greater than an alternator. I didn't even consider the alternator warranty issue when I made the choice go with DAR's on my own new boat, the decision was purely based on cost. In any case alternators are not known for unreliability. The mod BTW is simply to get a connection to one of the brushes.

 

You could have just the larger alternator feeding through the A to B to supply service and starter batteries. The smaller one with DAR fitted via a zero volt drop spllitter could feed service and BT batteries. This would still provide service battery charging redundancy in the unlikely event of either alternator failing.

 

ETA: FWIW the well proven setup on my boat is not that different from yours. The larger 160 amp alternator feeds the 550 Ah service bank directly. The smaller 90 amp one feeds starter, BT and service battery bank in that order via intelligent zero volt drop splitter. Both alternators employ the cheapest Sterling DAR's, with the smaller one connected to the splliters dedicated sense terminal. As already mentioned the 35mm2 BT charge cables don't create a volt drop issue. Since your needs and alternators are similar, I'm tempted to suggest this may suit you best.

This set up sounds good but the only thing I am not sure about is if it will equalise the batteries.

 

Neil

[by'eck]

This set up sounds good but the only thing I am not sure about is if it will equalise the batteries.

 

Neil

 

Apologies if I have it wrong but I suspect you do not fully appreciate what a true equalise charge is. This is a charge performed at the unusually high voltage of around 15.5 volts and then only on open lead acid batteries, in order to try to break down the sulphation crystals that have formed on the battery plates due to poor charging regimes, and so restore battery performance.

 

The term derives from the need to equalise the performance of the individual cells that make up the battery, since its likely that not all will be sulphated to the same degree. The high voltage forces current into the cells with the better ones simply gassing off the overcharge whilst others benefit to a greater degree, although there is never a guaranteed outcome.

 

In fact although I have the abilitiy, I have never found the need to perform a true equalise charge in nearly twenty years of use. Better to ensure the batteries are fully charged at the end of the day, and certainly not left flat or in a partially charged state for any length of time.

 

Your external alternator regulator, whatever type you choose, will ensure that batteries are charged at the most efficient voltage and drop to float when charge is complete. Regular charging of this nature is far more important than the ability to perform an equalise charge which is to some degree a closing the gate after the horse has bolted scenario.

Edited January 17, 2015 by by'eck

[Keith M]

Hello Neil

 

As promised I will have a look at the volt-drop in the bow thruster cables

As I see it there is two options

1 = Parallel the outputs of both alternators. This will give a slightly quicker re-charge time on the service battery

2 = Use the 50 amp alternator for re-charging the Starter battery and the Bow Thruster batteries. Once the alternator has re-charger the batteries it will have no work to.

 

Do we parallel or not this will depend on the service battery bank size ?

 

Personally I would not use an ALT / Battery charge system to parallel the alternator outputs. I would use a volt-drop free diode system. The reason for saying this is modern alternators now regulate to a much higher voltage than just a few years ago

 

As to volt-drop using 35 mm² cable

 

50 amp alternator the volt-drop will be 0.80-volts

Both alternators parallel the volt-drop 1.59-volts [i used a current flow of 100 amps. You have to start some where with type of calculation]

 

I hope the above is useful

 

Keith

 

 

Edited to add more imformation

Edited January 18, 2015 by Keith M

[Neil Smith]

Thanks Keith, that is indeed very helpful and as I understand it if the battery is low it will ask for a higher charge current but the volt drop on the smaller cable will be more and as it charges the draw will be less but volt drop wont be as much, or have I got that wrong.

By the way the sparks has done all the first fix apart from this charge cable as I never got any but can run that in myself.

 

Neil

[Keith M]

The volt-drop will change as the amps change

In the first example half the current the volt-drop will become 0.40-volts

 

By the way which system are you going for ? Are you going to parallel the alternators together

 

Keith