Disconnecting an alternator

[Col_T]

The boat was fitted with 5 * 110Ah sealed, lead acid batteries, for the domestic supply, when we bought it. I am now contemplating replacing those with a single Fogstar 300Ah LiFePO4 battery. The intention, at least initially, is to charge from our solar panels, so I’m thinking of installing a Victron SmartSolar MPPT, to take advantage of the built-in lithium charging algorithm.

 

The engine is a twin alternator BETA BV1505, and my thought is to disconnect the domestic alternator e.g. stop it from outputting to the LiFePO4 but, given that it provides the feed for the rev counter, the question is how?
 

It has its own isolation switch, but would using that just cause the ignition buzzer to sound the whole time, leave the domestic alternator warning lamp on, or do some harm to the alternator?

 

As a supplementary question, the domestic and engine battery alternators run different size pulleys so, I guess, run at different speeds per crank rotation. Presumably, swapping the rev counter feed from the domestic to the engine battery alternator, without some other change, would cause the rev counter to read incorrectly?

[eightacre]

Are you sure the rev counter is fed from the domestic alternator? Our boat has a BV1505 and the counter is fed from the engine alternator.

[phantom_iv]

Why don't you want to keep an alternator? Surely having more ways to charge your batteries is better than running out of power on a cloudy/rainy day?

 

If it were me I'd keep one of the leisure batteries connected to the alternator, use it as a buffer battery and fit a Victron Orion XS to charge your lithium battery from the old leisure - as a bonus it will communicate with the smartSolar over bluetooth and cooperate in charging the battery (for an extra bonus fit a smart shunt as well)

 

This way all everything works happily together, and if you run out of solar you can just start your engine as before.

[GUMPY]

At the risk of upsetting the purists 😱

You could as a temporary measure connect both alternators to the start battery. Its effectively what happened when my VSR joined my twin alternator on two batteries together.

 

[Tony Brooks]

11 minutes ago, Col_T said:

As a supplementary question, the domestic and engine battery alternators run different size pulleys so, I guess, run at different speeds per crank rotation. Presumably, swapping the rev counter feed from the domestic to the engine battery alternator, without some other change, would cause the rev counter to read incorrectly?

 

What @eightacre said - yours must be an unusual boat.

 

The majority of rev counters have little push button or switch on the back that lets you adjust the reading, so if you do as you suggest note the idle revs on the domestic alternator, swap the lead over, then adjust the rev counter to read as it did before. Read the manual for adjustment.

 

15 minutes ago, Col_T said:

It has its own isolation switch, but would using that just cause the ignition buzzer to sound the whole time, leave the domestic alternator warning lamp on, or do some harm to the alternator?

 

An alternator isolating switch???? The isolator switch usually isolates the whole domestic system from the battery, not just the alternator.

 

I think that if you pull the warning lamp wire off the alternator and tape it back on the loom, the light will not illuminate, the buzzer won't sound, and the alternator is very unlikely to charge. The only time disconnecting anything is likely to damage the alternator is if you do it when it is charging. If not energised it can run perfectly happily.

 

This assumes the domestic alternator is a nine  diode machine, which I think it is on Beta, Make sure the lamp is connected to a terminal marked D+

[Col_T]

3 hours ago, Tony Brooks said:

What @eightacre said - yours must be an unusual boat.

 . . . or I have mis-interpreted what I saw!! I’ll check next time I am on the boat.

 

Thanks for the responses.

[Tony Brooks]

5 minutes ago, Col_T said:

 . . . or I have mis-interpreted what I saw!! I’ll check next time I am on the boat.

 

Thanks for the responses.

 

The start alternator is usually the smaller one.

[ditchcrawler]

Most second domestic alternators run on a separate belt, take the belt off

[Jen-in-Wellies]

3 hours ago, phantom_iv said:

Why don't you want to keep an alternator? Surely having more ways to charge your batteries is better than running out of power on a cloudy/rainy day?

 

If it were me I'd keep one of the leisure batteries connected to the alternator, use it as a buffer battery and fit a Victron Orion XS to charge your lithium battery from the old leisure - as a bonus it will communicate with the smartSolar over bluetooth and cooperate in charging the battery (for an extra bonus fit a smart shunt as well)

 

This way all everything works happily together, and if you run out of solar you can just start your engine as before.

You can also fit a simple switch, wired across the Remote L H connections on any Victron  Orion B2B to disable them. I do this in summer, when solar supplies all my electrical use. Switch it back on, when required, over the darker months to suplement the solar. 

Posted this pic before.

 

The OP can install solar charged LiFePO4 now and won't have to make a decision on winter charging for a few months. 

[phantom_iv]

Good call! Does it save significant fuel usage if you go for a cruise in the summer though to turn off the Orion? Given that the solar will be running anyway, and assuming you're not setting off at dawn the solar will have put a chunk of charge into the batteries anyway?

 

In the short term the OP could always get rid of three of the existing batteries, and leave one there doing nothing but connected to the alternator (thus avoiding any issues disconnecting the alternator) and if you decide to put an Orion in later you've got a ready-made setup for it to source its power from.

[Jen-in-Wellies]

18 minutes ago, phantom_iv said:

Good call! Does it save significant fuel usage if you go for a cruise in the summer though to turn off the Orion? Given that the solar will be running anyway, and assuming you're not setting off at dawn the solar will have put a chunk of charge into the batteries anyway?

 

In the short term the OP could always get rid of three of the existing batteries, and leave one there doing nothing but connected to the alternator (thus avoiding any issues disconnecting the alternator) and if you decide to put an Orion in later you've got a ready-made setup for it to source its power from.

This was discussed recently. The answer is probably yes, the fuel saving from disabling them and using solar for Li charging is noticable. Given how inefficient alternators are. I just filled up the tank for the first time since the start of the Iran war and was surprised about how little I'd used, given the distance travelled. 146 miles and 112 narrow locks, taking 110litres. 

 

[IanD]

12 hours ago, Jen-in-Wellies said:

This was discussed recently. The answer is probably yes, the fuel saving from disabling them and using solar for Li charging is noticable. Given how inefficient alternators are. I just filled up the tank for the first time since the start of the Iran war and was surprised about how little I'd used, given the distance travelled. 146 miles and 112 narrow locks, taking 110litres. 

 

To give a comparative figure for a hybrid boat, my diesel usage since leaving the marina in the middle of May has been 60l -- which includes some for heating/hot water and generating domestic power -- to travel 125 miles with 152 locks in 20 days, that's 3l/day or 0.48l/mile compared to 0.75l/mile for Jen's diesel. That's with 99kWh (34%) coming from solar and 189kWh (66%) from the generator, typical for my (relatively heavy) use of the boat.

Edited Wednesday at 09:05 by IanD

[blackrose]

13 hours ago, Jen-in-Wellies said:

You can also fit a simple switch, wired across the Remote L H connections on any Victron  Orion B2B to disable them. I do this in summer, when solar supplies all my electrical use. Switch it back on, when required, over the darker months to suplement the solar. 

Posted this pic before.

 

The OP can install solar charged LiFePO4 now and won't have to make a decision on winter charging for a few months. 

 

Couldn't you just switch off the B2B using the Victron app rather than having a physical switch? I've probably misunderstood what you mean.

[BoatingLifeUpNorth2]

And now the thread goes completely off track and onto Victron blue boxes and electric boat efficiency over diesel discussion😂😂

Edited Wednesday at 09:36 by BoatingLifeUpNorth2

[blackrose]

17 hours ago, phantom_iv said:

Why don't you want to keep an alternator? Surely having more ways to charge your batteries is better than running out of power on a cloudy/rainy day? 

 

If it were me I'd keep one of the leisure batteries connected to the alternator, use it as a buffer battery and fit a Victron Orion XS to charge your lithium battery from the old leisure - as a bonus it will communicate with the smartSolar over bluetooth and cooperate in charging the battery

 

This is what I did, but if I were doing it again I wouldn't bother. It's an expensive faff and the benefits are minimal as I have to switch the Orion B2B down to 50% output anyway as advised to protect the buffer battery, so in practice I only have a 30A alternator. It might be worth it if the boat has a bigger alternator. When I'm cruising it's generally in spring or summer so the panels are charging anyway and I never use the engine to charge at my mooring as the generator is remotely located and extremely quiet (unlike the engine). My engine's water pump is driven from the start alternator belt, so if I were doing it again I'd just take the domestic alternator fan belt off. I've no idea about the revcounter though?

 

17 hours ago, Col_T said:

 

The boat was fitted with 5 * 110Ah sealed, lead acid batteries, for the domestic supply, when we bought it. I am now contemplating replacing those with a single Fogstar 300Ah LiFePO4 battery. The intention, at least initially, is to charge from our solar panels, so I’m thinking of installing a Victron SmartSolar MPPT, to take advantage of the built-in lithium charging algorithm.

 

The engine is a twin alternator BETA BV1505, and my thought is to disconnect the domestic alternator e.g. stop it from outputting to the LiFePO4 but, given that it provides the feed for the rev counter, the question is how?
 

It has its own isolation switch, but would using that just cause the ignition buzzer to sound the whole time, leave the domestic alternator warning lamp on, or do some harm to the alternator?

 

As a supplementary question, the domestic and engine battery alternators run different size pulleys so, I guess, run at different speeds per crank rotation. Presumably, swapping the rev counter feed from the domestic to the engine battery alternator, without some other change, would cause the rev counter to read incorrectly?

 

Try removing the domestic alternator fan belt, start the engine and see what happens to your revcounter.

Edited Wednesday at 09:57 by blackrose

[Tony Brooks]

3 minutes ago, blackrose said:

I have to switch the Orion B2B down to 50% output anyway as advised to protect the buffer battery,

 

Are you sure about that. I think it is usually advised to protect the alternator from burning itself out by prolonged running at maximum output - which LFP batteries allow. If I am correct then using the larger alternator to do the charging would let it run at a lower proportion of its maximum output.

Edited Wednesday at 09:40 by Tony Brooks

[blackrose]

14 minutes ago, Tony Brooks said:

 

Are you sure about that. I think it is usually advised to protect the alternator from burning itself out by prolonged running at maximum output - which LFP batteries allow. If I am correct then using the larger alternator to do the charging would let it run at a lower proportion of its maximum output.

 

I'm sure I was advised to turn the B2B down to 50%, but I'm not sure if that advice was correct.

Edited Wednesday at 09:54 by blackrose

[Tony Brooks]

33 minutes ago, blackrose said:

 

I'm sure I was advised to turn the B2B down to 50%, but I'm not sure if that advice was correct.

 

Fair enough, but as the buffer battery will not have any part is supplying the alternator current to the Li battery while the engine is running at normal speed, apart from the terminals acting as a junction box, I don't see how the reason you were given can be correct. I can see that limiting the B2B charging, and thus its input current, at 50% of the alternator's output would make sense in protecting the alternator which in most cases was never designed to provide 100% of its rated output for long periods.

[jonathanA]

2 hours ago, blackrose said:

as I have to switch the Orion B2B down to 50% output anyway as advised to protect the buffer battery, so in practice I only have a 30A alternator.

I think that advice is nuts or maybe you misunderstood.  I'm assuming the b2b is set up to detect engine running (default) and isn't trying to use the buffer battery on its own. (Wouldn't make any sense) 

 

As Tony says 50% of alternator rating is often quoted to be on the safe side. 

 

Personally I think that's a starting point, and it may be possible to increase the B2B current if the alternator temperature remains acceptable ... (however you define that !)

[Jen-in-Wellies]

Victron B2Bs will happily run at their rated current for hours. It's alternators that you need to limit the long term current draw on, with 50% being the accepted conservative maximum. 

[blackrose]

Maybe I misunderstood, but to be honest I still don't understand Tony's post or yours Jonathan. I have no control of alternator output apart from the internal resistance of the buffer battery itself. I thought that's what it was there for - to limit alternator output? So you're saying limiting B2B output to the Li batteries (which is all I can control) will have no effect on alternator output or buffer battery input voltage? In which case should I just reset the B2B to 100% (50A)? It's a 70A alternator.

 

Yes, my B2B detects engine running.

2 minutes ago, Jen-in-Wellies said:

Victron B2Bs will happily run at their rated current for hours. It's alternators that you need to limit the long term current draw on, with 50% being the accepted conservative maximum. 

 

But how do you do that?

[Jen-in-Wellies]

1 minute ago, blackrose said:

Maybe I misunderstood, but to be honest I still don't understand Tony's post or yours Jonathan. I have no control of alternator output apart from the internal resistance of the buffer battery itself. I thought that's what it was there for - to limit alternator output? So you're saying limiting B2B output to the Li batteries (which is all I can control) will have no effect on alternator output or buffer battery input voltage? In which case should I just reset the B2B to 100% (50A)? It's a 70A alternator.

 

Yes, my B2B detects engine running.

 

But how do you do that?

The buffer battery acts as a load to prevent reverse voltage spikes damaging the alternator when the Lithium battery disconnects when fully charged. The lead acid load battery will generally be fully charged, so will draw no current from the alternator. You limit the current that the B2B draws to feed the Li batt in the B2B configuration. See the screenshot of the Victron app below. Either input, or output current, or both. In practice, since the Orion XS B2B is so efficient and the charging voltages are similar, the input and output currents are similar. In your case, with a 70A alternator, you should set input current to 35A, 50% of 70A. You might as well leave output current at 50A, simce the input current will limit it to around that anyway. 

3 hours ago, blackrose said:

 

Couldn't you just switch off the B2B using the Victron app rather than having a physical switch? I've probably misunderstood what you mean.

You could. A switch is easier and quicker and you can see at a glance if it is enabled. KISS principle. 

[blackrose]

Ok got it, thanks.

 

For some reason I had both input and output set at 30A. I didn't realise I could set the input current. I've now got the input set at 35A and the output at 50A.

[ditchcrawler]

22 minutes ago, blackrose said:

Ok got it, thanks.

 

For some reason I had both input and output set at 30A. I didn't realise I could set the input current. I've now got the input set at 35A and the output at 50A.

You could monitor the temperature of your Alternator to see if you could increase that current at all for faster charging 

[Jen-in-Wellies]

19 minutes ago, ditchcrawler said:

You could monitor the temperature of your Alternator to see if you could increase that current at all for faster charging 

Is this the time to revive the usage of the forum term infrequent red thermometer? 😀(