Any battery experts?

[doug748]

As a follow up to the NASA Battery Monitor thread.

It was suggested that my battery may have been overcharging.

I have had my suspect 80Ah battery on overnight charge with ALDI's best 3.8 amp smart charger. I was surprised to see it fizzing a bit. Voltage on the meter 14.1 at rest 13.5. Is it possible that nackered, sulphated batteries tend to boil off the electrolyte and this accounts for the apparent overcharging and loss of fluid.

I am taking the thing to the local battery shop for testing but I am a bit wary; I have never had a battery test were the chap said:

" Excellent battery that mate"

It is always:

"Well, that's fooked"

They are selling stuff after all.

 

[halcyon]

Standing or charging voltage will tell you very little about battery condition. The battery seller will simply do a voltage drop test on the fully charged battery by applying a heavy load for a short period. If the voltage drops rapidly then the battery has poor capacity and is probably near or at the end of its useful life.

Ask to watch the test if you want to.

May use a modern meter that looks like a multimeter, gives state of charge, health of battery and more.

Brian

 

[VicS]

As a follow up to the NASA Battery Monitor thread.

It was suggested that my battery may have been overcharging.

I have had my suspect 80Ah battery on overnight charge with ALDI's best 3.8 amp smart charger. I was surprised to see it fizzing a bit. Voltage on the meter 14.1 at rest 13.5. Is it possible that nackered, sulphated batteries tend to boil off the electrolyte and this accounts for the apparent overcharging and loss of fluid.

I am taking the thing to the local battery shop for testing but I am a bit wary; I have never had a battery test were the chap said:

" Excellent battery that mate"

It is always:

"Well, that's fooked"

They are selling stuff after all.

A 3.8 amp charger is abit on the small size for an 80Ah battery. It should get there eventually but will take a long time from a deeply discharged state Id be looking at a charger with a max output of around 6 or 8 amps at least.

The first thing you can do is to charge it until the smart charger thinks its fully charged. Then let it stand with no load and no further charging for 12 hours.

Then check its volts with a reliable digital meter. It ought to be around 12.7. 12.8 better, 12.6 OK. If you cannot get it to charge to this level replace it!

Then let it stand and check how well it holds its charge. Although it will fall quickly at first it should take several weeks to fall below about 12.5.

If it falls below 12.5 in a few days its on its last legs. If it fall in a few hours replace it.

If it passes the above you can consider getting it tested to confirm that it really is good, but try to find somewhere that will use the sort of tester that Halcyon refers to ...... not just the old fashioned drop tester.

 

[GHA]

A voltage drop test is the simplest way for the home mechanic to test a battery. Charge it up and then connect it to an engine that has been disabled from starting in some way (on a boat engine diesel just ensure the engine stop is activated). Connect a volt meter to the battery and then crank the engine over for a while and note how fast the voltage is dropping. If it barely drops and returns to the same voltage as at the start of the test then the battery is fine.

OR possibly not fine, cca's don't appear to be a reliable indicator of capacity.

http://batteryuniversity.com/learn/article/how_to_measure_capacity

 

[lw395]

A battery can suffer from:
1) high resistance
2) self discharge
3)loss of capacity

1 matters a lot in a starting battery
2 matters in a battery that is idle for a long time
3 matters in a house battery

I wouldn't junk the battery in my car if it went flat after a month as I use the car almost daily.
It doesn't matter if the fridge battery won't start the engine, so long as it will run the fridge for long enough.

 

[VicS]

A voltage drop test is the simplest way for the home mechanic to test a battery. Charge it up and then connect it to an engine that has been disabled from starting in some way (on a boat engine diesel just ensure the engine stop is activated). Connect a volt meter to the battery and then crank the engine over for a while and note how fast the voltage is dropping. If it barely drops and returns to the same voltage as at the start of the test then the battery is fine.

I assume that by cca's you mean Cold Cranking Amps? If a batteries voltage drops rapidly when a heavy load is applied it is a simple indicator that the battery is not in particularly fine fettle. If the OP just wants to know whether to carry on using his battery for a bit longer it is an adequate enough test.

It will drop quite significantly while the engine is being cranked ! The question is just how far is acceptable.

More to the point ...... If it cranks the engine properly then its Ok . If its charged and there are no other faults or bad connections but wont crank the engine satisfactorily its no good, at least as a starter battery.

 

[doug748]

Well, well.

I took it along to the man and he attached his prehistoric machine, and he said it was charged ok and that it was fine. First time ever. So if you want an honest opinion go to EXE Batteries Plymouth, I say.

This is rather a disappointment as I now have to worry about what did cane my battery down to under 10v. The NASA monitor will help with this.

Thanks for all the suggestions. Whilst I am fitting my Battery Monitor I will have to upgrade a lot of the wiring so prepare yourselves for a lot of daft electrical questions over the winter.

 

[Roe]

Do you have a DC clamp meter? I recommend the uni-t one to my customers, I think it only measures 10A or so, but this is usually enough for diy trouble shooting. Stick it around the negative and measure the current draw with everything turned off. Then stick the main isolation switch on and then move through your switch panel until you find the problem appliance/cable.

 

[VicS]

Thanks for all the suggestions. Whilst I am fitting my Battery Monitor I will have to upgrade a lot of the wiring so prepare yourselves for a lot of daft electrical questions over the winter.

Be sure to fit the monitor exactly as described ....... no short cuts !

In particular there must be no connection, other than the shunt, to the house battery negative and no connections to that end of the shunt other than the battery negative and the white and black wires.

You might find this diagram helpful although NASa have improved their instructions a little since I drew it. ( I have not shown the orange wire for monitoring the start battery though as my diagram predates that facility. Use the same size fuse in that as supplied for the red wire)

 

[doug748]

Thanks for taking the trouble to post that VicS.

The problem for a electrical numnutt is figuring out how the electrical runs now, and fitting the new stuff correctly to it. However I am sure I will get there.

Think I will plumb in an automatic bilge pump whilst I am at it. That might be the subject of my next post.

PS

More strife, I have just read the post on Rule Auto pumps

 

[doug748]

Be sure to fit the monitor exactly as described ....... no short cuts !

In particular there must be no connection, other than the shunt, to the house battery negative and no connections to that end of the shunt other than the battery negative and the white and black wires.

You might find this diagram helpful although NASa have improved their instructions a little since I drew it. ( I have not shown the orange wire for monitoring the start battery though as my diagram predates that facility. Use the same size fuse in that as supplied for the red wire)

I have been thinking about this Vic and it has made my brain hurt.

As no other connections are allowed on the domestic negative or input side of the shunt......and bearing in mind that my engine can be started by, and charge, either battery using a simple 2 switch manual system.....

....It I relocate the existing HD start cable from the domestic negative to the "output" side of the shunt......

The engine start would work as now, and all would be well?

PS

Is the supplied wire, from battery neg to shunt, man enough for engine starting?

 

[pvb]

Reassuring to know that Doug's battery is OK. However, a single 80Ah battery really isn't enough to run basic lighting loads, let alone his autopilot. Surely it would be better to add another one or two batteries before going down the route of fitting a battery monitor?

 

[doug748]

After carting it back to the boat today, I have decided it is probably 100Ah.

Any views about the wiring?

 

[pvb]

After carting it back to the boat today, I have decided it is probably 100Ah.

Any views about the wiring?

100Ah still isn't enough. Spend your budget on more batteries!

 

[VicS]

I have been thinking about this Vic and it has made my brain hurt.

As no other connections are allowed on the domestic negative or input side of the shunt......and bearing in mind that my engine can be started by, and charge, either battery using a simple 2 switch manual system.....

....It I relocate the existing HD start cable from the domestic negative to the "output" side of the shunt......

The engine start would work as now, and all would be well?

PS

Is the supplied wire, from battery neg to shunt, man enough for engine starting?

Better to use a bus bar for all the negative connections than multiple connections on one terminal.

They say the cable supplied is heavy enough for the short duration of an engine start, but it really depends on how big the engine is. Presumably not a zillion horse power

 

[halcyon]

Better to use a bus bar for all the negative connections than multiple connections on one terminal.

They say the cable supplied is heavy enough for the short duration of an engine start, but it really depends on how big the engine is. Presumably not a zillion horse power

You do not need a zillion horse power, a 3 YM15 starter pulls 250 am, stall 600 amp, that is when it starts to turn the engine so zero rpm of stater motor.

Brian

 

[VicS]

You do not need a zillion horse power, a 3 YM15 starter pulls 250 am, stall 600 amp, that is when it starts to turn the engine so zero rpm of stater motor.

Brian

I missed where he said it was a 3YM15

 

[doug748]

Better to use a bus bar for all the negative connections than multiple connections on one terminal.

They say the cable supplied is heavy enough for the short duration of an engine start, but it really depends on how big the engine is. Presumably not a zillion horse power

Thank you Vic, the key thing is I do nothing daft electrically. I may well fit the bus bar. The engine is a modern 20hp triple. I will probably stick with the NASA cable because the times I start on the domestic battery are pretty much limited.


pvb. Thanks, I have had no problems with battery capacity.