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Okay, here's one way of doing it...

  • Small alternator charges Starter Batt via an isolator
  • Large alternator charges Leisure Batts via an isolator
  • BT Batts have their own isolator
  • VSR fed by Leisure Batts feeds long 10mm2 cables which link the BT Batts to the Leisure Batts with a 100A fuse at each end of that cable.

Hope that helps, Tony

Edited by WotEver
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9 hours ago, WotEver said:

Okay, here's one way of doing it...

  • Small alternator charges Starter Batt via an isolator
  • Large alternator charges Leisure Batts via an isolator
  • BT Batts have their own isolator
  • VSR fed by Leisure Batts feeds long 10mm2 cables which link the BT Batts to the Leisure Batts with a 100A fuse at each end of that cable.

Hope that helps, Tony

I think it depends on the expected usage of the BT. If the BT is rarely used, - just for the odd unusual circumstance, which is how it should be IMO - then this is fine.

But if the boat is virtually steered around on the BT, using it instead of bothering to move the tiller - which seems to be an increasing and silly fad - then that configuration may fail to keep the BT batteries adequately charged, due to voltage drop in the long cables. After using the BT one really needs to keep the engine running for a long time to fully recharge the BT batteries and avoid sulphation. In this case it may be advisable to use much thicker cable and larger fuses - costly and bulky. Alternatively, to avoid the problem of high currents and voltage drop, you might consider moving the energy at high voltage. So, presuming a decent inverter is fitted, run mains cable to the front and have a dedicated battery charger for the BT batteries.

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2 minutes ago, nicknorman said:

I think it depends on the expected usage of the BT. If the BT is rarely used, - just for the odd unusual circumstance, which is how it should be IMO - then this is fine.

<big snip>

... presuming a decent inverter is fitted, run mains cable to the front and have a dedicated battery charger for the BT batteries.

Agreed. I did say that was one way of doing it.

If the BT is going to be abused then the 230/charger method would be far superior (although of course, more expensive and something else to break). 

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13 hours ago, WotEver said:

Hope that helps, Tony

It does. Thank you Tony. Would be much easier if you guys came to sunny (rain soaked) Cornwall for a week and did all this for me!!!! But then I`d get "no satisfaction" as Jagger sings- don`t think he was speaking of 12 volt electrics though!

4 hours ago, nicknorman said:

expected usage of the BT.

Hopefully avoiding to many difficulties due to wind when arriving and leaving mooring. No fun not learning to do it properly.

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5 hours ago, nicknorman said:

Alternatively, to avoid the problem of high currents and voltage drop, you might consider moving the energy at high voltage. So, presuming a decent inverter is fitted, run mains cable to the front and have a dedicated battery charger for the BT batteries.

This is what my boat has. Not that I use the BT much. Last time I used it was to steer in reverse out of Glascote Basin on a windy day.  Didn't want to scratch any of the pristine Hudsons moored there :P

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On my twin alternator system one alternator is dedicated to the domestic battery bank while the charge from the other alternator gets split by a VSR between the start battery and the BT batteries at the bow (and they should be at the bow). The logic of this system is that the start battery remains largely charged or if not will charge quicker than the domestic bank, so the "spare" charge can be directed to the BT batteries.

I don't use the BT that much but I've never run down the batteries and the charge cable from the stern to the bow is only 16mm2. But you should have short fat cables from the batteries to the BT.

image.png.dc2dca1a45dd3e9b25f0345de832acde.png

I also have these BEP master switches.

image.png.b5c3da7871c93b96c8f29a25cbc3458f.png

Edited by blackrose
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On 01/08/2017 at 07:44, nicknorman said:

Alternatively, to avoid the problem of high currents and voltage drop, you might consider moving the energy at high voltage. So, presuming a decent inverter is fitted, run mains cable to the front and have a dedicated battery charger for the BT batteries.

Which is effectively using the domestic batteries to charge the BT batteries - while the engine is running.

It's what a lot of people do, but in my experience if there is a decent 12v charging system and the BT is not abused, there should be no need for a mains charger at the bow.

Edited by blackrose
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2 minutes ago, blackrose said:

Which is effectively using the domestic batteries to charge the BT batteries - while the engine is running.

Well it's using the domestic alternator to charge the BT batteries while the engine is running, and using the domestic batteries to charge the BT batteries when the engine is not running.

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On 31/07/2017 at 22:30, WotEver said:

 

  • VSR fed by Leisure Batts feeds long 10mm2 cables which link the BT Batts to the Leisure Batts with a 100A fuse at each end of that cable.

 

Better to have the VSR fed by start battery for the reasons stated in my previous post.

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Just now, nicknorman said:

Well it's using the domestic alternator to charge the BT batteries while the engine is running, and using the domestic batteries to charge the BT batteries when the engine is not running.

You would keep the BT mains charger switched on using the inverter while the engine isn't running?

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2 minutes ago, blackrose said:

Better to have the VSR fed by start battery for the reasons stated in my previous post.

I doubt it would make much difference in reality but I take your point. 

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Just now, blackrose said:

Better to have the VSR fed by start battery for the reasons stated in my previous post.

It just depends on the alternator sizes and battery sizes. On our boat we have a 175A domestic alternator. Within a few minutes of starting the charge current is down around 100A since the batteries won't take more current. So plenty of spare capacity for a BT charger. The engine alternator is only 45A.

if we had say a 70A domestic alternator I'd probably not want the BT batteries being charge by it. 

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1 minute ago, blackrose said:

You would keep the BT mains charger switched on using the inverter while the engine isn't running?

If you're a BT Abuser then you'd have to. 

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1 minute ago, blackrose said:

You would keep the BT mains charger switched on using the inverter while the engine isn't running?

No I think that would be unnecessarily wasteful. But if stopping the engine for a while (lunchtime etc) I would. One of the things that kills batteries is failing to fully recharge. A BT is likely to be used when "parking" the boat, and then if the engine is stopped the BT batteries won't get fully charged, sulphation will set in.

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1 minute ago, blackrose said:

On my setup the BT batteries get charged anytime the main battery charger is switched on via the VSR because I have a charger feed going to the start battery.

That's no different to what I described originally. 

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9 minutes ago, nicknorman said:

It just depends on the alternator sizes and battery sizes. On our boat we have a 175A domestic alternator. Within a few minutes of starting the charge current is down around 100A since the batteries won't take more current. So plenty of spare capacity for a BT charger. The engine alternator is only 45A.

if we had say a 70A domestic alternator I'd probably not want the BT batteries being charge by it. 

Yes, that's all I've got 2 x 70amp alternators. So in my case it seems much more logical to have the BT charge split from the start battery because the start alternator would be largely laying idle if it only had to charge the start battery (which generally starts out well-charged), while the domestic alternator is working hard to charge a big bank.

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1 hour ago, blackrose said:

Yes, that's all I've got 2 x 70amp alternators. So in my case it seems much more logical to have the BT charge split from the start battery because the start alternator would be largely laying idle if it only had to charge the start battery (which generally starts out well-charged), while the domestic alternator is working hard to charge a big bank.

However, OP who asked the question has a big Beta, so has a large domestic alternator, hence my suggestion that using the spare capacity from that alternator was 'one way to do it'. 

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On 07/31/2017 at 22:30, WotEver said:

Okay, here's one way of doing it...

  • Small alternator charges Starter Batt via an isolator
  • Large alternator charges Leisure Batts via an isolator
  • BT Batts have their own isolator
  • VSR fed by Leisure Batts feeds long 10mm2 cables which link the BT Batts to the Leisure Batts with a 100A fuse at each end of that cable.

Hope that helps, Tony

This is how my BT battery is wired, except for the VSR. The advantage to this setup is that the BT battery is effectively part of the domestic bank. The disadvantage to this setup is that the BT battery is effectively part of the domestic bank.

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1 hour ago, aread2 said:

This is how my BT battery is wired, except for the VSR. The advantage to this setup is that the BT battery is effectively part of the domestic bank. The disadvantage to this setup is that the BT battery is effectively part of the domestic bank.

That about sums it up. 

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