Batteries at the sharp end

[Big Steve]

I'm toying with the idea of putting the batteries at the front of the boat. being a big lad, and so is my co pilot, the boat looks like it's about to go on the plane when we are motoring. It struck me that shoving the leisure batteries down the front would balance the boat a bit better, enable me to be able to get more batteries on board, and free up some space in the engine bay.

 

I can see drawbacks like volts drop when charging, I don't see a drawback for the loads, as they are all in the middle of the boat anyway.

 

I've been a bit surprised at the V drop with even 16mm cable, but in practice, will it really be a problem? The boat is used for cruising and doesn't have a huge electrical load.

 

Has anyone done this?

 

[Guest]

I'm toying with the idea of putting the batteries at the front of the boat. being a big lad, and so is my co pilot, the boat looks like it's about to go on the plane when we are motoring. It struck me that shoving the leisure batteries down the front would balance the boat a bit better, enable me to be able to get more batteries on board, and free up some space in the engine bay.

 

I can see drawbacks like volts drop when charging, I don't see a drawback for the loads, as they are all in the middle of the boat anyway.

 

I've been a bit surprised at the V drop with even 16mm cable, but in practice, will it really be a problem? The boat is used for cruising and doesn't have a huge electrical load.

 

Has anyone done this?

 

I think you will struggle with the charging regime personally. I kept the batteries as near to the alternator as possible, but then again I have no external regulators or similar. I am unsure if anything like this would help the situation. I understand people have problems getting sufficient charge into bow thruster batteries in a reasonable time, but again, I don't have one.

[chris w]

I'm toying with the idea of putting the batteries at the front of the boat. being a big lad, and so is my co pilot, the boat looks like it's about to go on the plane when we are motoring. It struck me that shoving the leisure batteries down the front would balance the boat a bit better, enable me to be able to get more batteries on board, and free up some space in the engine bay.

 

I can see drawbacks like volts drop when charging, I don't see a drawback for the loads, as they are all in the middle of the boat anyway.

 

I've been a bit surprised at the V drop with even 16mm cable, but in practice, will it really be a problem? The boat is used for cruising and doesn't have a huge electrical load.

 

Has anyone done this?

 

It won't work steve.

 

The volts drop (or lack of it) for charging is extremely important. It shouldn't be more than 0.1v or say 0.2v at absolute tops.

 

So, running the maths, for a 60 ft (20m) boat the cable size needed to ensure no more than a 0.2v drop when charging at 40A is:

 

17x10^-3x40 x 40/0.2 = 136mm² !!!!!!!!!

 

Chris

[Gibbo]

I can see drawbacks like volts drop when charging, I don't see a drawback for the loads, as they are all in the middle of the boat anyway.

 

I've been a bit surprised at the V drop with even 16mm cable, but in practice, will it really be a problem? The boat is used for cruising and doesn't have a huge electrical load.

 

I second Chris.

 

You say "bit surprised at the V drop with even 16mm cable" as if 16mm cable is big. I'm just running from engine room to boatman's cabin and am using a mixture of 70mm, 95mm and 120mm to keep losses down to sensible levels. If you tried 16mm from one end of the boat to the other I'd be surprised if there was any charge current left at all by the time it got there.

 

Gibbo

[Nickhlx]

I second Chris.

 

You say "bit surprised at the V drop with even 16mm cable" as if 16mm cable is big. I'm just running from engine room to boatman's cabin and am using a mixture of 70mm, 95mm and 120mm to keep losses down to sensible levels. If you tried 16mm from one end of the boat to the other I'd be surprised if there was any charge current left at all by the time it got there.

 

Gibbo

 

So what do people with bow thrusters do ? Have a 50 or 100 amp charger at the front, running off their mains ?

 

Nick

[Gibbo]

So what do people with bow thrusters do ? Have a 50 or 100 amp charger at the front, running off their mains ?

 

Nick

 

Why would anyone suggest a 50 or 100 amp charger for a little battery? 10 or 15 amp charger yes. I have seen those. I've even installed them.

 

If charging from the alternator most people use cable substantially bigger than the 16mm suggested by OP for a start. Usually 40mm upwards. I've never used anything less than 70mm on a narrowboat.

 

But you also have to remember that (assuming it isn't a pillock driving the boat who thinks the BT is a tiller extension) a bow thruster gets use more like an engine start battery. It isn't (or rather shouldn't) be deeply discharged like a domestic bank is. It is also somewhat smaller. The result being the required charge currents are much smaller, for a much shorter time and the total energy that has to be returned is much smaller, so overall losses (although still important) are nowhere near the issue they would be with a domestic bank.

 

Gibbo

[Nickhlx]

Why would anyone suggest a 50 or 100 amp charger for a little battery? 10 or 15 amp charger yes. I have seen those. I've even installed them.

 

If charging from the alternator most people use cable substantially bigger than the 16mm suggested by OP for a start. Usually 40mm upwards. I've never used anything less than 70mm on a narrowboat.

 

But you also have to remember that (assuming it isn't a pillock driving the boat who thinks the BT is a tiller extension) a bow thruster gets use more like an engine start battery. It isn't (or rather shouldn't) be deeply discharged like a domestic bank is. It is also somewhat smaller. The result being the required charge currents are much smaller, for a much shorter time and the total energy that has to be returned is much smaller, so overall losses (although still important) are nowhere near the issue they would be with a domestic bank.

 

Gibbo

 

I was "exaggerating a touch" !! There are 2 x 110 aH batts on one I looked at a few weeks ago but didn't think about charging arrangements at the time - as you say a few bursts of assistance throughout the day should be replenished quite quickly - and possibly wouldnt even need two batteries..

 

Nick

[Big Steve]

Thanks for the comments, you've put paid to that idea. I'm so used to 240v, 16mm is big.

 

Now I'm struggling 'cos there's no room for any more batteries in the engine bay. I suppose I'm just being greedy, the old tub has got by with one 110Ah domestic battery for so long I thought it might be time to increase it. I'll just have to learn to live with it.

[chris w]

Thanks for the comments, you've put paid to that idea. I'm so used to 240v, 16mm is big.

 

Now I'm struggling 'cos there's no room for any more batteries in the engine bay. I suppose I'm just being greedy, the old tub has got by with one 110Ah domestic battery for so long I thought it might be time to increase it. I'll just have to learn to live with it.

Just out of interest, if you did run 16mm² all the way to the bow (and back again, of course), and you were trying to charge at 40A, the volts drop would be almost 2 volts !!!! Not a lot of charging would happen

 

Chris

[bottle]

Steve

 

You could always buy a bigger battery, ampere wise.

 

Just ensure their physical size will fit.

[MikeV]

Steve,

 

If you have mains generation such as a TravelPower you could place a large battery charger next to the batteries driven off the 240V circuit. Some boat builders seem to use mains battery chargers as standard now rather than use a 12V alternator for charging.

 

Downside would be be increased losses though the TravelPower and possibly shorter life on the TravelPower alternator.

 

Another possibility would be an alternator-to-battery charger, again located near the batteries. CLICKY This would restore the volt drop losses on the long cable run. You would still probably need at least 50 sqmm cable so that the volt drop is less than 1 volt allowing the 14 volts at the alternator to drop to 13V at the alternator-to-battery charger input.

 

Neither of these are optimal, would be less energy efficient and add cost to the overall installation, but would allow you to have the batteries at the front. Obviously if you have an inverter, this also need to be sited close to the batteries.

 

Edited for spellin'

Edited March 3, 2009 by MikeV

[twocvbloke]

If you need more weight at the front, just get some more ballast, I'm sure there's plenty of railway track available (not fitted onto a line of course!!!) that you can cut up into bitesized chunks, and distribute about the fore end to get an even balance...

 

Either that or lay off the KFC!!!

[smileypete]

Hi,

 

If I had no choice but to put the battery bank at the bow, I'd consider moving the alternator regulator to the bow as well!

 

I'd use about 10mm for the three 'phase' wires from stern to bow, and a couple of smaller cables for the field supply back.

 

Also I'd make an external diode 'pack' for the regulator using 'schottky' power diodes.

 

The lower voltage drop of 'schottky' diodes will more-or-less compensate for losses in the long phase cables.

 

Means learning a bit about alternators, but you get perfect battery voltage compensation for free

 

cheers,

Pete.

 

Edit:

 

I expect Gibbo will come along sometime and shoot me down in flames

Edited March 3, 2009 by smileypete

[chris w]

Hi,

 

If I had no choice but to put the battery bank at the bow, I'd consider moving the alternator regulator to the bow as well!

 

I'd use about 10mm for the three 'phase' wires from stern to bow, and a couple of smaller cables for the field supply back.

 

Also I'd make an external diode 'pack' for the regulator using 'schottky' power diodes.

 

The lower voltage drop of 'schottky' diodes will more-or-less compensate for losses in the long phase cables.

 

Means learning a bit about alternators, but you get perfect battery voltage compensation for free

 

cheers,

Pete.

 

Edit:

 

I expect Gibbo will come along sometime and shoot me down in flames

 

Many if not most alternators have the brushes as an integral part of the regulator assembly (which is also usually sealed) so it would be a very difficut result to achieve in practice. Far easier would be to convert the alternator to battery sensing and run a "sense" cable from the battery to the alternator.

 

Chris

[BlueStringPudding]

Thanks for the comments, you've put paid to that idea. I'm so used to 240v, 16mm is big.

 

Now I'm struggling 'cos there's no room for any more batteries in the engine bay. I suppose I'm just being greedy, the old tub has got by with one 110Ah domestic battery for so long I thought it might be time to increase it. I'll just have to learn to live with it.

 

If it's just about power, is there any room inside the boat for additional batteries - such as a cupboard in the aft cabin that could be sealed inside and safely vented outside? Or a stern locker that's already outside but could be converted? It'd save running long lengths of expensive cable.

 

Do you have a separate starter battery? I know some boats that don't meaning you could connect both batteries for domestic and starter power (just don't run them till they're empty). Our starter battery is another standard 110Ah battery same as all the rest, yours might be too.

 

As for the ballast thing, just stick summit heavy down at the bow to level you out a bit (concrete slabs or a stage weight (they're very compact and very heavy), or make sure your water tank is good and full before you cruise!

 

(End of uneducated layperson contribution)

Edited March 3, 2009 by BlueStringPudding

[Nickhlx]

If it's just about power, is there any room inside the boat for additional batteries - such as a cupboard in the aft cabin that could be sealed inside and safely vented outside? Or a stern locker that's already outside but could be converted? It'd save running long lengths of expensive cable.

 

Do you have a separate starter battery? I know some boats that don't meaning you could connect both batteries for domestic and starter power (just don't run them till they're empty). Our starter battery is another standard 110Ah battery same as all the rest, yours might be too.

 

As for the ballast thing, just stick summit heavy down at the bow to level you out a bit (concrete slabs or a stage weight (they're very compact and very heavy), or make sure your water tank is good and full before you cruise!

 

(End of uneducated layperson contribution)

 

 

Yes but...

 

if the batteries are at the back near the alternator, and the bow thruster is at the, err... bow (!), I assume it takes quite a current ( 100 amps ?) so you would have to run even bigger cables to it to minimise the volt drop, wouldn't you ?

 

Whats the optimum answer for those with a bow thruster ?

 

Nick

[davidandheather]

Yes but...

 

if the batteries are at the back near the alternator, and the bow thruster is at the, err... bow (!), I assume it takes quite a current ( 100 amps ?) so you would have to run even bigger cables to it to minimise the volt drop, wouldn't you ?

 

Whats the optimum answer for those with a bow thruster ?

 

Nick

Our bow thruster batteries are at the front of the boat and are charged by the 45 amp starter alternator via very thick cables.

We have never yet had a problem using this system in 4 years not that we use the bow thruster much.

David

[Nickhlx]

Our bow thruster batteries are at the front of the boat and are charged by the 45 amp starter alternator via very thick cables.

We have never yet had a problem using this system in 4 years not that we use the bow thruster much.

David

 

 

Seems the only option to me - ( front batteries / very thick cables to charge )

 

What size ( mm2) cables are they ( or diameter if you can't remember) ?

 

Nick

Edited March 3, 2009 by Nickhlx

[davidandheather]

Seems the only option to me - ( front batteries / very thick cables to charge )

 

What size ( mm2) cables are they ( or diameter if you can't remember) ?

 

Nick

I did not build the boat we had it done for us so not sure of the size but they were very big from what i can remember, they looked like big armor cables i will have a look at the weekend.

David

Edited March 3, 2009 by davidandheather

[Big Steve]

Thanks again for all the ideas,

 

I'm thinking

 

Use the starter battery alternator to drive a nearby inverter when the engine is running, run the 240v to the bow, use this to charge the bow battery bank.(via a charger)

Retain the original setup (starter battery and domestic battery in engine 'ole with separate alternators)

Feed both domestic 12v supplies to a centrally situated fuse box.

 

I realise that isolation relays/switches will be needed, imbalance of battery charge won't be a problem because the cable resistance will stop any current surges.

The efficiency of the inverter isn't an issue because this bit only works when the engine is running, and compared with the engine efficiency it's wonderful. I have 2 small ones lying about spare, so the cost doesn't matter, but they're pretty cheap now anyway.

 

I'm only doing this because :

 

I'm renewing the boat lining

The existing wiring is all less than 1mm²

I think I need more battery capacity (though110Ah as been plenty for ages)

I need more ballast up the front

 

I could just stick with what I've got but improve the wiring, and I could probably get another 110 Ah battery in the engine 'ole. Should I do this and stick some bits of railway line in the bow? Can you use scrap batteries for ballast? Drained and flushed with bicarb they shouldn't be hazardous, should they?

 

As for 70mm² cable !!

[chris w]

I did not build the boat we had it done for us so not sure of the size but they were very big from what i can remember, they looked like big armor cables i will have a look at the weekend.

David

Out of interest, run the bow thruster a few times to gve a realistic discharge then measure the voltage at the bow thruster batteries when they are on charge.

 

Chris

Edited March 3, 2009 by chris w

[Gibbo]

Steve that sounds like a decent solution.

 

You could wire up another relay energised from the ind (D+) on the engine start alternator and use the contacts to switch the inverter on and off. Then it's totally automatic and you can't forget and leave it switched on.

 

Nothing wrong with flushed batteries for ballast. Saves taking them to the tip.

 

Gibbo

[Big Steve]

Steve that sounds like a decent solution.

 

You could wire up another relay energised from the ind (D+) on the engine start alternator and use the contacts to switch the inverter on and off. Then it's totally automatic and you can't forget and leave it switched on.

 

Nothing wrong with flushed batteries for ballast. Saves taking them to the tip.

 

Gibbo

 

Thanks Gibbo, the tip on the auto switch is good.

[smileypete]

Many if not most alternators have the brushes as an integral part of the regulator assembly (which is also usually sealed) so it would be a very difficut result to achieve in practice. Far easier would be to convert the alternator to battery sensing and run a "sense" cable from the battery to the alternator.

 

How would you do that?

 

I'd consider getting a cheap A127 regulator and using as an external regulator at the battery end.

 

It's field connection would just connect in parallel with the alternator's regulator field connection.

 

cheers,

Pete.

[chris w]

How would you do that?

 

I'd consider getting a cheap A127 regulator and using as an external regulator at the battery end.

 

It's field connection would just connect in parallel with the alternator's regulator field connection.

 

cheers,

Pete.

No need to do that.Think about how the regulator senses the battery at the moment on an A127 (and most other alternators). An internal connection is taken from the battery through a couple of diodes (to ensure that what the battery and the regulator are seeing is identical) and on to the regulator.

 

So one could simply take a single lead from the battery at the bow, fit 2 series diodes into the lead (to equalise the voltage drop owing to the field diodes) and plug this lead on to the regulator input spade (having first disconnected the existing wire).

 

Chris