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Battery levels


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I’ve got 2 x 110Ah leisure batteries and a starter battery. I got fed up with contorting myself to check their state of charge with a multimeter and wanted something that would make life easier for me and give me an idea of what was being put into the leisure batteries and what was being drawn out.

I settled for a NASA BM1 battery monitor, which gives me a continual indication of the leisure bank’s voltage, % charge, and amps going in or out, and shows me the voltage of the starter battery. The amps in/out facility is useful for monitoring the performance of your alternator/battery charger/solar panel.

The installation kit was sufficient for the leisure bank installation. The option of monitoring the starter battery is available by buying an extra bit of wire and an in-line fuse. It’s not strictly necessary to monitor the starter battery, as it takes very little drain and is (or should be) fully charged after running the engine for a short time. But the option exists, so I got the extra bit of wire and fuse.

 

The installation instructions were very, very detailed and easy to follow.

 

Of course, other battery monitors are available. Smartgauge do one, for example, but it is more expensive than the BM1 and doesn’t show the amps in and out.

If you don’t want to go to the expense of a battery monitor and just want to know your battery’s voltage, a £5 multimeter will do the job.


 

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Voltage is absolutely no indication of the condition of the battery and so a multimeter will easily give you a very false sense of how well the battery will perform once you start using it.

 

Specific gravity of the electrolyte is a much better indication to the state of charge of the battery, but this is much more difficult to get a reading on as you need direct access to all the cells. In situe, this may be very difficult and dangerous. Plus, with sealed batteries, it is also impossible.

 

A good battery monitor needs to be able to measure the voltage & amps in and out (as Mark says), but to be really useful, it needs to log this data over time so see how well it takes a charge, how long it takes to discharge given a known draw and how well it maintains a charge between charges and use. It also needs to know about the battery types and ratings. These things must exist, but I am unaware of them. They can't be cheap as these will be embedded CPU systems with quite complex software.

 

A multimeter will give you the voltage at the terminals, but provides no load on the battery. So, you might have 13.8 volts with the battery at rest, but what happens to that when you fire the Webasto? The amp draw for the glow plug in a diesel cabin heater is high and a poor battery showing 13.8v at the terminal might instantly drop to 12v the moment you put a big load on it and only return to 12.4 (say) once that load is removed. A multimeter will show this, but ONLY is you operate it in conjunction with a load.

 

Battery condition, charging and so on is a HIGE topic full of complex issues.

 

All we generally want is this: to know that the boat will start after being left for a few weeks and that the systems will serve us well for the duration of our use. The best solution then, is to install a charging system to maintain the batteries during periods of absence.

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All we generally want is this: to know that the boat will start after being left for a few weeks and that the systems will serve us well for the duration of our use. The best solution then, is to install a charging system to maintain the batteries during periods of absence.

Absolutely, Andy.

 

With that system in situ onboard Friday Girl we've had the same start/services batteries for over 4 years and they weren't anywhere new when we bought the boat!

 

That being said we bought new ones just after the Horning boat show because the old ones were gassing continously and needed topping up quite frequently.

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Now if someone could come up with a monitoring system that recorded the specific gravity of the electrolyte and its level in the batteries, they would have a licence to print money.

 

Our battery box is in the most awkward place in the engine bay, oh for the want of one of these boats you just walk down a ladder into the engine bay and casually walk around the one or two engines and see all of the equipement that is easy to work on, instead you get scatched to death cramped double after removing heating ducts and any other items that impead you progress to get to the items you wish to look at.

 

Regards

Alan

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All we generally want is this: to know that the boat will start after being left for a few weeks and that the systems will serve us well for the duration of our use. The best solution then, is to install a charging system to maintain the batteries during periods of absence.

 

A word of caution : any charging system that is to be left unattended should be current-limited. If a battery develops a fault, such as a shorted cell, that drops it's terminal voltage this could cause a high current to be drawn from a normal constant-voltage charger with the danger of fire and/or explosion. This has been known to happen.

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Thank you all for your reply's.

 

I have two 110ah leisure batteries, one 110ah starter battery and one 110ah battery for the Bow Thruster  and Mud Weight electric winch.

 

When on shore power they are charged on a professional charging system, Sterling I think.

 

So when I go cruising I know that all batteries should be fully charged, then topped up from the alternator.

 

Why I asked the original question was, obviously, after mooring for the night the batteries need recharging by running the engine.

 

I understand that the general rule is 3 - 4 hours engine time to top up the batteries.

 

Sometimes after mooring overnight we feel like an hours leisurely cruise is as far as we want to go and then moor up for the night again.

 

My main concern then is how much power is left in the leisure batteries?

 

Seeing a Battery condition gauge that showed the needle simply showing red, orange and green I thought this was my answer.

 

But, by the replies you have kindly given I have dug myself a hole.

 

After reading up about the NASA BM1 suggested by PALADIN I think this could be what I am after.

 

One of the settings that shows battery level and predicted hours left at that consumption looks great.

 

At my local chandlers they are £92.99 inc. vat.

 

 

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Something you could consider doing as well is to replace all your lighting with LED's. We have a total of 15 lights on Secret Lady which all had 10W halogen bulbs, each drawing nearly an amp (not that they were usually on all the time of course) and the drain shown on the ammeter was quite considerable. We have since swapped these for warm white LED's which give just as much light but barely register on the ammeter when on.

 

Obviously this doesn't refer to you original question at all, but does help conserve battery power when off shorepower for a night or two.

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Hi 10B,

I assume that Mark will have done the same as everyone else and just replaced the inserts in his light fittings this was all I did and I replaced a similar amount to Mark, I did leave the uplighters (only two on the boat) and the two reading lamps we have in the aft cabin.

I tried them out with some different wattage inserts that Brian Ward's allowed me to trial prior to purchase.

Regards

Alan

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I would suggest you add a solar charging system (proper job not micky mouse) then when you are moored without shore power you will still be getting a top up to those batteries, A good quality controller (or regulator if you like) will make all the difference to the solar system.

 

or just turn all that stuff off and enjoy the peace and tranquility then the battery capacity will last a lot further!

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Something you could consider doing as well is to replace all your lighting with LED's. We have a total of 15 lights on Secret Lady which all had 10W halogen bulbs, each drawing nearly an amp (not that they were usually on all the time of course) and the drain shown on the ammeter was quite considerable. We have since swapped these for warm white LED's which give just as much light but barely register on the ammeter when on.

 

Is something like this what you have in mind, Mark?

 

http://www.ebay.co.uk/itm/4-x-12v-G4-LED-BULBS-LAMPS-WITH-30-x-3528-LEDS-DAY-COOL-20W-HALOGEN-CAPSULE-/270873807875?_trksid=p2054897.l4275

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BLIMEY, I have only been a simple salesman all my working life, now you are throwing all these lethal looking objects at me.

 

I'm having a party on my boat, all ELECTRICIANS, BOAT BUILDERS AND BRAIN SURGEONS WELCOME. cheersbar

 

Must bring your tools with you!!!!!!!!!!!!! :clap

 

Date: after the 16th, I will bring my tools to help. Fish2

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.................oh for the want of one of these boats you just walk down a ladder into the engine bay and casually walk around the one or two engines and see all of the equipement that is easy to work on...
 
 
 
 
But it wouldn't fit under Potter Bridge! :-)
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Thanks bird, I have just bought one that has a sensor on it.

I am going to fit this in the toilet compartment.

Did you change the complete unit or just the fittings?

 

Just changed the bulbs themselves, not the fittings. I got the 24 SMD ones off eBay to ensure they were good and bright.

 

I have stuck some of the motion sensor ones in cupboards and wardrobes too, so they come on when you open the door and stick your hand in. Very handy for dark spaces! They were these ones when Amazon had them for about £5 each http://www.amazon.co.uk/Philips-SpotOn-Motion-Sensor-One-Pack/dp/B000PVX678/ref=pd_sim_light_9?ie=UTF8&refRID=1KF4EY69S11KKYGGRNES

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  • 2 months later...

post-29388-0-91520500-1407602375_thumb.j

 

Fitted, thanks for all your assistance.

 

What has it found?

 

1st trip out the batteries were fully charged, going down the river the monitor was showing a discharge, next morning  monitor showed 80% charge.

Set off expecting to see % charge increase, no still showing discharge.

Moored up for night, checked fitting instructions, all looked ok.

Next morning 60% charge.

 

Not being electrical minded, get system checked.

 

Batteries not charging, main lead from alternator missing!!!

Because this was missing the alternator has not been sending out power to batteries which has damaged it.

New alternator fitted.

Cable from splitter to front battery not thick enough.

Splitter wired wrongly.

 

Luckily unbeknown to me we have been surviving on shore power.

 

Because of the help from the forum I may be able to relax now. cheersbar  :clap

 

 

 

 

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Note to monitor your battery installs.

At work we have 3 backup m/c incase of power cuts they each have 33 yuasa sealed 96Ahr blocks in each kept around 19c to take the load for 20 seconds till backup gen set kicks in.

The blocks didn't show any indication of faults ie floating at zero charge. 6 years old and within 3 weeks there was blown blocks in each unit. Full swap needed. That bad egg smell was all the indication we needed.

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