24DC Charging question

[Blue Seas]

Hi Folks,

I have read lots of threads on the subject but I still have an unanswered question if I may,

3 BATTERY BANKS - All Rolls AGM. Starter is 100ah Rolls x 2 (24v) Domestic and Bow banks are 2 X Rolls 230ah each set up in series for 24v.
Starter and domestic banks are next to each other and only 1 meter from the engine so no issues.
Bow bank is however almost 10 meters from the alternator and domestic bank - so potential issues with cable length in emergency cross-connection.
I have read Paul Rainbow's suggestion of 3 - output shore charger and 3 output Argofet and that appeals as a simple solution but is that the best way to get power over the 10 meter distance?
The charger is comparatively easy as I could position it at mid-point and still stay within the maximum 6 meter cable length advised by Victron - but the alternator output (via Argofet) might be more problematic.
Would I be better fitting a second charger up in the bow and feed that with 240v from the Victron inverter (3KW) which could in turn be supplied from the alternator via domestic bank i.e. Use 240v to go the 10 meters rather than 24v? That still leaves the issue of emergency DC cross connection though?
Thanks in advance for your thoughts.
Steve

 

[geem]

Hi Folks,

I have read lots of threads on the subject but I still have an unanswered question if I may,

3 BATTERY BANKS - All Rolls AGM. Starter is 100ah Rolls x 2 (24v) Domestic and Bow banks are 2 X Rolls 230ah each set up in series for 24v.
Starter and domestic banks are next to each other and only 1 meter from the engine so no issues.
Bow bank is however almost 10 meters from the alternator and domestic bank - so potential issues with cable length in emergency cross-connection.
I have read Paul Rainbow's suggestion of 3 - output shore charger and 3 output Argofet and that appeals as a simple solution but is that the best way to get power over the 10 meter distance?
The charger is comparatively easy as I could position it at mid-point and still stay within the maximum 6 meter cable length advised by Victron - but the alternator output (via Argofet) might be more problematic.
Would I be better fitting a second charger up in the bow and feed that with 240v from the Victron inverter (3KW) which could in turn be supplied from the alternator via domestic bank i.e. Use 240v to go the 10 meters rather than 24v? That still leaves the issue of emergency DC cross connection though?
Thanks in advance for your thoughts.
Steve

To clarify, you have a 24v bow thruster and or windlass?

 

[Sandy]

Would I be better fitting a second charger up in the bow and feed that with 240v from the Victron inverter (3KW) which could in turn be supplied from the alternator via domestic bank i.e. Use 240v to go the 10 meters rather than 24v? That still leaves the issue of emergency DC cross connection though?

Are you proposing taking DC turning it into AC to charge a DC battery?

If you are that sounds madness very inefficient.

Fit some heavy duty wire and charge from your current set up. It is not as if the bow batteries are going to be used a lot.

 

[PaulRainbow]

To clarify, you have a 24v bow thruster and or windlass?

From post #1 :

"3 BATTERY BANKS - All Rolls AGM. Starter is 100ah Rolls x 2 (24v) Domestic and Bow banks are 2 X Rolls 230ah each set up in series for 24v.

 

[Blue Seas]

Yes 24v bow thruster (Sleipner) and yes all systems 24v including starter and alternator

 

[Blue Seas]

To clarify;
Bow = 2x 12v 230ah setup as 24v
Ditto Domestic
Engine start 2x 12v 100ah each again set up as 24v

 

[PaulRainbow]

A pair of 16mm cables to the bow will carry 30a without too much voltage drop for charging.

You would normally only have an emergency parallel switch between the engine and domestic bank.

 

[Blue Seas]

A pair of 16mm cables to the bow will carry 30a without too much voltage drop for charging.

You would normally only have an emergency parallel switch between the engine and domestic bank.

I was thinking mainly of the ‘return’ path I.e. I have a spare 460ah in the bow should I inadvertently (or fault) discharge the domestics.
Maybe a 50a b2b?

 

[PaulRainbow]

I was thinking mainly of the ‘return’ path I.e. I have a spare 460ah in the bow should I inadvertently (or fault) discharge the domestics.
Maybe a 50a b2b?

16mm cables would be adequate for domestic loads up to at leat 30a.

A 24v - 24v B2B charger would need 16mm cables, so no benefit.

 

[Blue Seas]

16mm cables would be adequate for domestic loads up to at leat 30a.

A 24v - 24v B2B charger would need 16mm cables, so no benefit.

16mm cables would be adequate for domestic loads up to at leat 30a.

A 24v - 24v B2B charger would need 16mm cables, so no benefit.

My apologies Paul, I have not explained myself adequately.
The existing cables are already bigger than 16mm (I’ll check exactly what tomorrow) so that is not the issue.
Let’s say, in simplistic terms, that I have an almost flat domestic bank of 460ah 24v - but I have a fully charged bow bank of the same capacity.
Whilst I do not know the answer to my own original question (obviously) - I do know that I cannot just cross connect and ‘dump’ a load of 460ah over 10 meters via 16mm or anything close.
So how do I safely balance 460ah fully charged into 460ah seriously discharged over 10M?
Sorry for the confusion- I’m thinking it through as we go.
Thanks
Steve

 

[geem]

My apologies Paul, I have not explained myself adequately.
The existing cables are already bigger than 16mm (I’ll check exactly what tomorrow) so that is not the issue.
Let’s say, in simplistic terms, that I have an almost flat domestic bank of 460ah 24v - but I have a fully charged bow bank of the same capacity.
Whilst I do not know the answer to my own original question (obviously) - I do know that I cannot just cross connect and ‘dump’ a load of 460ah over 10 meters via 16mm or anything close.
So how do I safely balance 460ah fully charged into 460ah seriously discharged over 10M?
Sorry for the confusion- I’m thinking it through as we go.
Thanks
Steve

I am trying to work out why you have bow batteries at all. That was the reason for clarifying that everything at the bow was 24v. The volt drop at 24v is so low that you can easily run cable at reasonable cost from your domestic batteries to run windlass and bow thruster. I can't help thinking that a simpler system would be better and no weight of two 12v batteries in the bow.

 

[Blue Seas]

I am trying to work out why you have bow batteries at all. That was the reason for clarifying that everything at the bow was 24v. The volt drop at 24v is so low that you can easily run cable at reasonable cost from your domestic batteries to run windlass and bow thruster. I can't help thinking that a simpler system would be better and no weight of two 12v batteries in the bow.

Thruster is 15hp
Anchor winch / windlass is hydraulic

 

[Blue Seas]

I am trying to work out why you have bow batteries at all. That was the reason for clarifying that everything at the bow was 24v. The volt drop at 24v is so low that you can easily run cable at reasonable cost from your domestic batteries to run windlass and bow thruster. I can't help thinking that a simpler system would be better and no weight of two 12v batteries in the bow.

Both work fine

 

[William_H]

The reason boats go 24v system is that current for the same power is one half of that for 12v but also that any volt drop in wiring becomes less significant (half) in relation to supply voltage. So volt drop in wiring is much less concern. (OP is fortunate)
I would suggest a simple solution might be to permanently connect bow bank to domestic bank. So charging becomes a simple problem of charging 2 isolated batteries from on alternator or charger. (engine and domestic) Use diodes or VSR. This arrangement will give you double the domestic capacity while still giving power for thruster from bow battery backed up by domestic battery.
Of course there is much to be said for running thruster and anchor winch directly from engine start battery. On the assumption that engine will be running when you use both those, but that does assume engine alternator can cope with the high current demand. (at idle speed)
As said it may be an over kill to have batteries in the bow for thruster with a 24v system but if you already have it and weight is not a problem then leave as is. (until batteries need replacing) ol'will

 

[Sandy]

My apologies Paul, I have not explained myself adequately.
The existing cables are already bigger than 16mm (I’ll check exactly what tomorrow) so that is not the issue.
Let’s say, in simplistic terms, that I have an almost flat domestic bank of 460ah 24v - but I have a fully charged bow bank of the same capacity.
Whilst I do not know the answer to my own original question (obviously) - I do know that I cannot just cross connect and ‘dump’ a load of 460ah over 10 meters via 16mm or anything close.
So how do I safely balance 460ah fully charged into 460ah seriously discharged over 10M?
Sorry for the confusion- I’m thinking it through as we go.
Thanks
Steve

You charge the domestic bank from whatever you charge them normally with, e.g. engine, generator, solar or wind.

If you have allowed your domestic bank to become so low you need to consider using the bow batteries as your domestics you are not managing your usage.

 

[Blue Seas]

The reason boats go 24v system is that current for the same power is one half of that for 12v but also that any volt drop in wiring becomes less significant (half) in relation to supply voltage. So volt drop in wiring is much less concern. (OP is fortunate)
I would suggest a simple solution might be to permanently connect bow bank to domestic bank. So charging becomes a simple problem of charging 2 isolated batteries from on alternator or charger. (engine and domestic) Use diodes or VSR. This arrangement will give you double the domestic capacity while still giving power for thruster from bow battery backed up by domestic battery.
Of course there is much to be said for running thruster and anchor winch directly from engine start battery. On the assumption that engine will be running when you use both those, but that does assume engine alternator can cope with the high current demand. (at idle speed)
As said it may be an over kill to have batteries in the bow for thruster with a 24v system but if you already have it and weight is not a problem then leave as is. (until batteries need replacing) ol'will

I am giving serious consideration to combining them as you say, with perhaps auto isolation in event of reaching a pre-set low voltage.

 

[Blue Seas]

You charge the domestic bank from whatever you charge them normally with, e.g. engine, generator, solar or wind.

If you have allowed your domestic bank to become so low you need to consider using the bow batteries as your domestics you are not managing your usage.

I seem to have 'managed my usage' successfully for 51 years - I'm talking about a potential fault situation dropping one bank or the other - it would be ridiculous to have a back up fully charged bank and not be able to transfer in such an event (once the fault is rectified) it would it not?

 

[Sandy]

I seem to have 'managed my usage' successfully for 51 years - I'm talking about a potential fault situation dropping one bank or the other - it would be ridiculous to have a back up fully charged bank and not be able to transfer in such an event (once the fault is rectified) it would it not?

If it is that catastrophic then swap your batteries.

 

[Blue Seas]

If it is that catastrophic then swap your batteries.

Crikey, I forgot all about the mid-atlantic battery shop, silly me.

 

[Sandy]

Crikey, I forgot all about the mid-atlantic battery shop, silly me.

I'm out. You are just being silly.