NASA battery monitor

[muckypup]

Just fitted a NASA battery monitor today. Nice device, works well. I noticed a couple of things....

1) I have a split charge diode installed, and when the engine is running it's only putting in about 12.5v / 5amps. I assmume that it's putting the same to the starter battery... 10amps. So why is the alternator rated to 70amps if it only pushes out 10?

2) When I turn everything off except for the bilge alarms and a gas alarm it still says the 300milliamps is being drawn (turning off the isolation switch correctly drops this to zero). Is this normal? or does it seem a little high?

Steve

 

[Guest]

An alternator only whacks out full amps when batterys are well down and near flat. As they charge up - the resistance builds and charge rate drops .....

IMHO - I'm no leckie !! But 10A is still a fair wack showing batterys are part down.

As to the 300mA .... do you have small items that are drawing monitoring current while rest switched of ? Or you may have stray current leakage via a ground or other connection ?

 

[boatbuilder]

300ma sounds about right for gas alarm

 

[Rick]

Sounds as if you have a charging problem, as at lower voltages, current should rise - at 12.5 volts my 70 amp alternator is working hard (50 amps or so at 6,000 alternator rpm), however after an hour or so, voltage is up and over 14, and current output minimal (<10).
Is the 12.5 volts / 5 amps with engine running at above idle?

300 milliamps seems a lot - can you isolate and check which alarm it is, or whether with them off, you still have a loss?

 

[Guest]

Voltage ....

Could he have a voltage reduction because of the diode splitter ? They normally reckon about 0.7V drop across them. But surely the NASA monitor is showing battery volts - not charging volts ???????

 

[john_morris_uk]

Not convinced about the charging problem from the evidence that is given.

The amount that the alternator puts into the batteries depends on a couple of factors: what the state of charge is of the batteries, and how hot the alternator is.

An alternator is rated at xx amps 'when cold'. As soon as the alternator warms up, the output will be reduced. It is VERY rare for a 90Amp alternator to actually charge at 90 amps. For example our charging system has an alternator smart controller and full monitoring system and I know to be working very well. When the batteries are 40% discharged the 90 amp alternator, when first turned on, will charge at 50 or 60 amps. As the batteries charge up, this decreases to typically 25 amps until when nearly fully charged, about 10 amps.

My question is whether the alternator have any battery sensing or other compensation for the split charging diodes? If it does not, this is a major fault in the design of the system and needs to be addressed.

 

[muckypup]

The domestics are nearly dead. I put 2 new 120ah batteries in. No idea what state of charge they were. Unfortunately where I am berthed I have no shore power. These batteries had 1 hour of gene charging at about 10amps in 4 weeks. What I had not realised was that the 300ma drain over 4 weeks adds up to quite a lot and 2 nearly dead batteries (in fact not even enough to run the chart plotter).

So the split charge diode was still only putting in 5 amps with the main engine running. In fact the battery monitor was claiming I needed to run the engines for 50 hours for a full charge /forums/images/graemlins/shocked.gif

It's not something simple like it's only giving out enough amps for the lowest denominator, ie the engine starter battery? If it decided to punp out 20amps because the domestics needed it, this would be much more than the engine starter battery would require and possibly damage it?

Do split charge diodes always give 50/50 output?

Steve

 

[halcyon]

The problem is 12.5 volt.
Check the voltages from the alternator output at all connections to battery, and make a note of volt drops. It's possible your alternator is running at 13.6 volt regulation, and your droping 1.1 volt in the diode pack. not unknown. Or you have a bad connection, hard to say till you have some system voltages. But you need to see 14.0 / 14.4 volt at the batteries, you may need to invest in smart regulator to improve the situation.

300 ma is ok.

Brian

 

[muckypup]

Before the diode was installed, it was charging it's own starter battery at over over 13v according to the meters on the dash. Must be the diode....

Steve

 

[halcyon]

If you had satifactory charge level before fitting the diodes, then it may be cheaper to change it for a VSR, than boost the the alternator output.
But I would still run round with a voltmeter to check for a bad joint.

Brian

 

[john_morris_uk]

If you have completely discharged the batteries at any time, and left them for some time in a discharged state, then they will have lost some if not most of their capacity. You need to get them off the boat and get them fully charged up as soon as possible. It is possible that the new batteries are already destroyed

Can you confirm that you have a standard alternator with no external alternator regulator? Can you confirm that you have connected the alternator to the two batteries through the diode splitter? If so, there are three or four possible ways to sort things out. The diode splitter does NOT split the current 50-50. The battery that is most discharged will always accept the greatest charge. The physics of the battery sorts it out.

Finally, why not isolate the batteries when you leave the boat? Most people isolate everything when they leave their boats. It's safer and it saves the slow discharge that you have experienced. 300 ma over four weeks is over 200 Amp-hours so no wonder the batteries are flat!

 

[Guest]

The split diodes will allow what is necessary toi each battery. They have no part to play in equal splitting ... it is the internal resistance of each battery that determines charge to it.

I have an increasing suspicion that you have fitted a split diode system to a normal machine sensed alternator - this will not work well and would meaan batterys never being charged.
In fact when I tried it ... the diodes knocked my charge back so bad - it was pointless having them. Only solution would be to cheat the alternator sense or fit battery sense lead. In the end I disconnected the split diode and went back to battery switch .. which returned charging to healthy levels.

 

[ccscott49]

Get a smart charger alternator controller, with a seperate battery volatge sensor lead, connected to your domestic batteries. The diode pack is dropping your charge voltage, but I would also expect your alternator to be putting out more than 10 amps, because if it senses only 12.5 volts, it thinks the batteries are almost flat, so it should be ramming it in! Machine sensed alternators in this day and age are poo!

 

[muckypup]

Yeah... Now I have seen the problem, I have put an hours worth of charge into the batteries via the gene and then flicked everything off via the isolating switch. They were not completely dead, but down to just under 10v. Suprisingly the Navman VHF worked fine at this voltage.

It is the standard alternator with no more external gubbins. I took a feed with 70amp wire from the alternator to the diode, and from the diode direct to each battery bank.

I have 2 x 120ah batteries in parallel, so I set up the NASA battery monitor as 240ah. Correct?

Steve

 

[Guest]

To be honest ... as John Morris says get those batterys home and charged up as soon as possible. (I have had batterys discharged lower than 10v and still managed to get them back up .................).

IMHO - I would remove that split diode and either a) revert to a switched system - simple and battery gets full charge available - even if you put to both - you will get amps / volts delivered, or b) change for a VSR controlled system - where you don't get the voltage drop as with diodes.

Of course you can go the way of smart alternator controller ... only question I have then is - is alternator man enough for it ?

 

[muckypup]

I shall have to think on this some more.

One of the Sterling jobbies is about £200 and Harlequins engine bay is very very full of stuff, I'm not sure where I would mount this.

You have got me wondering now if a simple 2 position switch might be the cheaper and simpler long term solution. All of the switches I can find seem to be 1, 2 or all. I would be nervous putting one of these in just in case I accidentally selected all.

You you switch this over with the engine running?

S.

 

[Guest]

The 1-both-2-Off switch is built having make before break contacts .... so as long as you do not select OFF while engine running - no problem.

I have luxury of shore power - so have a charge splitter between car charger and batts. But when away from shore power and charging from engine .....>

Start engine on engine batt. (position 2 on my switch). Chug out of marina still on position 2....... for 30 mins or so - this puts back start use. Then change switch to BOTH ... to give domestic a top-up. Stop engine and then switch back to domestic position 1 to run nav gear etc.
Arrive of next place and switch to position 2 start engine .... short run on position 2 - then back to BOTH. Tie up .... stop engine ... back to Position 1. (it is true that its a pain sometimes remembering and often I forget .... but my Domestic and start are both capable of doing each others jobs ....)

There are better ways of doing it than the above switch ... but none cheaper !

The only thing really to remember - never switch to OFF when engine is running. Even if you have alternator with protective circuitry .....

 

[Otter]

I agree, there are more complicated and sophisticated ways of doing what you need, but for the £30 a 1,2,both,off switch will cost you, you would solve all your present battery probs. The 'off' switch would prevent battery drain caused by your stray 300ma and keeping one of the batteries for engine starts would ensure that is ready when needed. The NASA monitor could then be attached to your domestic battery and monitor its need for charging. All this would allow the removal of the split charge diode and the problems it is causing your alternator. But whatever you do, get the batteries home ASAP and use a mains charger to get them up to full charge. Then leave them for 48 hours and measure the voltage. If the voltage is lower than 12.3 after two days rest from charging, you have suffered serrious long term damage and you should consider replacing one and using it just for engine starts.

 

[Guest]

Thanks .... my idea would be to :

Go back to simple set-up and then sort from there.

KDD power ... who posts on here has VSR set-ups that could be added later - as do other outlets ... so once charging is sorted and at good levels, by removing problems - then start looking at ways to make life easier.

The guy who set-up my battery banks made one mistake that should be sorted ... he has some items wired via fuses direct to one or other battery - so that 1-B-2-O switch is partially bypassed..... VHF Radio - OK accepted, Coolbox ! ????..... plus a couple of silly items ...

 

[muckypup]

I can see that a switch one way or another might be a good cheap way to go, but worried about the off/both of those switches if accidentally selected.

If off, then it would isloate the alternator from both batteries... Will this not cause it to burn out the alternator?

What happens when set to both? Isn't there an issue here which is why split charge diodes were invented in the first place?

S.

PS. Marina have assured me that my pontoon will have shorepower by thursday this week!! hurrah! I will believe it when I see it though.