Three battery banks

[oldade]

Hi

Help needed.

I am looking for a charging system for my new boat.

I will have three battery banks

My main question is about how to charge the BT batterys.

Which system would work best ?

 

Sterling says run 25mm cables to the BT bank and use one of theyer battery to battery chargers.

Whould that be any good ?

 

I see Gibbo does a three bank system which is the one I fancy.

But I need to know that it will charge the BT batterys fully given the length of cable ? (57ft)

 

Will the 25mm cables as sterling recomends be big enough to allow the BT batterys to charge fully ?

How do the chargers / relays know / mesure the charge in the BT batterys ?

 

I dont understand why I need a battery to battery charger as sterling recomends ?

 

If I just connect the BT batterys direct via a fuse at each end to one of the rear banks what will / won't happen ?

 

Thanks

I have learned a lot in a very stort time from all you guys.

 

THANKS

again and in advance

ADE

[blackrose]

Hi

Help needed.

I am looking for a charging system for my new boat.

I will have three battery banks

My main question is about how to charge the BT batterys.

Which system would work best ?

 

Sterling says run 25mm cables to the BT bank and use one of theyer battery to battery chargers.

Whould that be any good ?

 

I see Gibbo does a three bank system which is the one I fancy.

But I need to know that it will charge the BT batterys fully given the length of cable ? (57ft)

 

Will the 25mm cables as sterling recomends be big enough to allow the BT batterys to charge fully ?

How do the chargers / relays know / mesure the charge in the BT batterys ?

 

I dont understand why I need a battery to battery charger as sterling recomends ?

 

If I just connect the BT batterys direct via a fuse at each end to one of the rear banks what will / won't happen ?

 

Thanks

I have learned a lot in a very stort time from all you guys.

 

THANKS

again and in advance

ADE

 

By 3 banks do you mean start, domestics & BT?

 

If 25mm2 cable is quoted by Sterling then he will also have quoted a maximum distance to avoid voltage drop. I think there is a table somewhere in the instructions for the new range of Sterling chargers. (My chandler showed me the table and as a guide I used 25mm2 cable from a 40amp charger at a distance of about 3 metres).

 

It's difficult for anyone to answer the last part as we don't know your system. Different boats use different systems to charge BT batteries. My BT batteries are connected to the start battery alternator and the charge is switched by a relay from one bank to the other as certain voltages are reached. All I did was to connect one terminal of the 3 output Sterling charger to the start battery and the relay does the same thing. It's only really important to charge BT & start batteries if you're moored up for long periods without starting the engine, but if you're on shore power they may as well be maintained by a constant float charge and a weekly full charge cycle (by switching it off and back on - although some chargers do this themselves).

[Smelly]

If in doubt, ask Tony...

 

http://www.tb-training.co.uk/MarineE03.html#VOLTDROP

[Gibbo]

Hi

Help needed.

I am looking for a charging system for my new boat.

I will have three battery banks

My main question is about how to charge the BT batterys.

Which system would work best ?

 

Sterling says run 25mm cables to the BT bank and use one of theyer battery to battery chargers.

Whould that be any good ?

 

Yes. Obviously the bigger the better but it's not *that* critical for charging a bow thruster battery. The losses in thinner cable will reduce the charge current and therefore increase the charge time, but not by as much as you'd expect. Halving the cross sectional area of the cable might increase the charge time by (say) 20% or so. It will NOT affect the final state of charge. That will be the same whatever size cable is used and is dependant upon the charge voltage not the current.

 

Before anyone pipes up that thinner cable will lead to voltage losses, that only applies when current is being drawn through them. As the batteries charge up, the charge current (and therefore the voltage drop) reduces so the batteries still receive the full charge voltage.

 

The other thing to consider is that unless the pilot is a complete novice the BT battery doesn't get used much and there is plenty of cruising time available to fully recharge it.

 

I see Gibbo does a three bank system which is the one I fancy.

But I need to know that it will charge the BT batterys fully given the length of cable ? (57ft)

 

See above. The length and size of cable does not affect whether or not the batteries get fully charged. Only how long it takes.

 

Will the 25mm cables as sterling recomends be big enough to allow the BT batterys to charge fully ?

How do the chargers / relays know / mesure the charge in the BT batterys ?

 

Chargers don't measure the state of charge of the batteries. They measure the current going into the batteries. When it drops below a certain level they decide they are full. That's as much as they know. The length and size of cable will make very little difference to this.

 

I dont understand why I need a battery to battery charger as sterling recomends ?

 

If you only want to charge the BT battery whilst cruising then a simple relay split charge system controlled from the alternator will be perfectly adequate.

 

There is a slight issue here in that if (for whatever reason) the BT battery is flat when the BT is operated and the engine is running then the BT will draw its power form the batteries at the stern. That in itself isn't a problem (assuming your split charge relay is big enough) but..........

 

If I just connect the BT batterys direct via a fuse at each end to one of the rear banks what will / won't happen ?

 

I see you intend to do it properly and use fuses. Many people don't and that is really quite dangerous. The problem is that the fuses will blow (see paragraph above).

 

What you have to do is take a signal from the BT control panel and use that to disable the split charge relay when the BT is operated. That stops the fuse from blowing. It's quite a common trick done by many marine engineers.

 

If you also want to charge the BT and engine start batteries from a mains powered charger then you will need a charger with 3 outputs. If you only have a single output charger then our gadget will take care of that or so will the battery to battery charger. However that's only really necessary if the boat is going to be left for lengthy periods of time (say more than 2 months or so) without running the engine.

 

If you don't want to use the signal from the BT panel to interrupt the split charge relay then the battery to battery charger will allow this without problem and will also charge the BT battery form the mains powered charger.

 

In summary.

 

If you only want to charge the BT battery whilst cruising then a simple relay energised form the alternator will suffice. You will need to interrupt the relay signal when operating the BT (signal available in BT control panel).

 

If you want to charge the BT battery from the mains charger you will either need to use our device and hack into the BT control panel OR use a simple relay arrangement and a 3 output charger OR use the battery to battery charger.

 

If you refuse to hack into the BT panel you have no choice other than to use the battery to battery charger (olther than to fit no fuses).

 

Gibbo

[smileypete]

If you only want to charge the BT battery whilst cruising then a simple relay energised form the alternator will suffice.

 

Could the relay switch on a small inverter which in turn powers a small charger for the BT batteries?

 

The charger could be near the BT batteries too, and would only need small mains flex run down the boat instead of thick DC cables.

 

When the boat is unattended for long periods on a shoreline, the charger could be plugged into the shoreline instead.

 

Edit:

 

Something I'd also consider is a small panel voltmeter to monitor the bowthruster batteries.

 

cheers,

Pete.

Edited June 22, 2008 by smileypete

[Gibbo]

Could the relay switch on a small inverter which in turn powers a small charger for the BT batteries?

 

I've actually done that on a few installations. Mainly on big stuff though. 120 foot plus. On a narrowboat it costs more than decent cable and is, obviously, less reliable.

 

Something I'd also consider is a small panel voltmeter to monitor the bowthruster batteries.

 

Everytime I think about this one I come to the same conclusion. "What's the point in monitoring the voltage of a battery that you won't do anything about anyway?"

 

You arrange the system so the BT battery is always charged when on shorepower and when the engine is running. That's it. If it's flat you're not gonna start the engine just to charge that battery.

 

Gibbo

[smileypete]

Everytime I think about this one I come to the same conclusion. "What's the point in monitoring the voltage of a battery that you won't do anything about anyway?"

 

You arrange the system so the BT battery is always charged when on shorepower and when the engine is running. That's it. If it's flat you're not gonna start the engine just to charge that battery.

 

For powering a BT I'd consider running square aluminum bar in conduit from the back of the boat.

 

Bit tricky to fit and connect to, but 3/4" bar is equivalent to 220mm² copper. That'll do.

 

At about £6/metre it's not outrageously expensive either:

 

http://www.metals4u.co.uk/detail.asp?Cat_I...&Prd_ID=895

 

cheers,

Pete.

[DHutch]

For powering a BT I'd consider running square aluminum bar in conduit from the back of the boat.

 

Bit tricky to fit and connect to, but 3/4" bar is equivalent to 220mm² copper. That'll do.

 

At about £6/metre it's not outrageously expensive either:

 

http://www.metals4u.co.uk/detail.asp?Cat_I...&Prd_ID=895

 

cheers,

Pete.

Technical against BSS regs. Although your right, there are many reasons to do it, and its been dont before.

[Gibbo]

Technical against BSS regs.

 

Which part of the BSS prohibits that?

 

Gibbo

[oldade]

Hi

Thanks to you all for that.

A question to Gibbo.

You say get a signal from the BT control panel and feed it to the split charge relay that feeds the BT Batterys.

I am guessing that you are getting the BT control panel to open the relay to the BT Batterys and saving the fuses that way?

 

I can see how that works because as soon as the BT is turned off the relay will close again and start to topup the BT batterys again.

Have I got it right ?

Would your three bank gaget be better suited to this set up than you two bank version ?

Thanks for everyones help with this it is much clearer now how this all works .

 

Just a thought ( I now I shouldnt do it ) I will need two feeds from the BT control panel wont I because of the two directions ?

Can I just join into the cable that goes postitve in each direction ? as that would save opening the BT control panel.

 

Would the current from the BT cable be enough to operate the charge relay and the BT without blowing a fuse or damaging the BT control panel ?

Have I got this right ?

Thanks very much to you all for this.

ADE

[Gibbo]

Hi

Thanks to you all for that.

A question to Gibbo.

You say get a signal from the BT control panel and feed it to the split charge relay that feeds the BT Batterys.

I am guessing that you are getting the BT control panel to open the relay to the BT Batterys and saving the fuses that way?

 

Correct. That's all it does. Via a small relay.

 

I can see how that works because as soon as the BT is turned off the relay will close again and start to topup the BT batterys again.

Have I got it right ?

 

You got it.

 

Would your three bank gaget be better suited to this set up than you two bank version ?

 

The 3 bank version is now exactly the same as the 2 bank version but it has two relays. It only senses on the first 2 battery banks. The old 3 bank version (which sensed on all 3 banks) was never used as no one ever charges to the third battery bank so it has been disocntinued.

 

Thanks for everyones help with this it is much clearer now how this all works .

 

Just a thought ( I now I shouldnt do it ) I will need two feeds from the BT control panel wont I because of the two directions ?

Can I just join into the cable that goes postitve in each direction ? as that would save opening the BT control panel.

 

There are various versions of the control panels. Some have a separate feed for each direction. With that type you need to stick two diodes in there. Most of them have a signal that goes positive if the BT is being used in any direction. With that type you just use that signal to energise a relay. You use the normally closed position of the relay and use the contacts to interrupt the feed to the split charge relay.

 

Would the current from the BT cable be enough to operate the charge relay and the BT without blowing a fuse or damaging the BT control panel ?

 

It doesn't operate the split charge relay. It operates a small relay which in itself operates the split charge relay. The small relay uses next to nothing (about 0.1 Amps)

 

You only need our device if you want to charge all the batteries from shorepower.

 

Gibbo

[oldade]

Hi

Question for Gibbo ( again Sorry )

Could I trouble you for a wiring diagram ?

I only need the bit with the relays and diodes in.

 

I am sorry if I am being a pain .

 

My email if you want to send it direct.

oldade@btinternet.com

 

If it is a lot a work I will understand.

 

Thanks very much again

ADE

[Gibbo]

Hi

Question for Gibbo ( again Sorry )

Could I trouble you for a wiring diagram ?

I only need the bit with the relays and diodes in.

 

I am sorry if I am being a pain .

 

My email if you want to send it direct.

oldade@btinternet.com

 

If it is a lot a work I will understand.

 

Thanks very much again

ADE

 

I'll find time this weekend to do a diagram and email it to you. Can't fit it in until then.

 

Are you using a normal split charge relay energised from the alternator?

 

Gibbo

[oldade]

I'll find time this weekend to do a diagram and email it to you. Can't fit it in until then.

 

Are you using a normal split charge relay energised from the alternator?

 

Gibbo

Hi

Again

Its a new build

 

I will be using your gear I hope

The engine is a canalstar 30 with 50amp and 110 amp alterntors.

120ah start battery 550 ah domestic 220ah BT batterys.

Could you send me a list of what I would need.

And the cost as well.

I am looking for a top notch system ( not cutting corners )

I have all the battery cables fuses etc

I have read all your web site and will be following that.

 

Thanks a lot again

ADE

[Guest melodyman]

Is 1 battery one bank?