Genset Battery

[Dave Liquorice]

So you have a small open frame genset with 12 V electric start.

Said genset has a 12 V battery charging abilty.

Would you expect it to charge its own battery when running?

[tabbypurr]

Thank you, much appreciated.

If I designed it, yes. If I paid a shockingly low price for it I'd expect any sneaky scheme the mfr could pull to save 5p.

NT

[Nick]

No, and yes. No, I don't have such a set. Used to have a Honda of this flavour. Yes, it should charge its own battery. I don't know of any electric start engine that does not have inbuilt battery charging apparatus.

[Dave Liquorice]

So that's four of us (SWMBO'd also expected it to charge it's own battery).

Well it's no-name Chinese single cylinder diesel so I guess they have saved their 5p.

The battery charging terminals hit about 30 V open circuit dropping to 15 V @ 7 to 8A across the (old, removed and partially dead) battery. Measure the volts of the gensets (new, installed) battery and they are about 12.9 just after starting the set slowly rising to

13.5 ish. Makes no difference if the set is running or not. Obviously not being charged.

Pretty sure I've seen a wiring diagram for it somewhere but can't find it now. B-(

[tabbypurr]

Sounds like it's not under guarantee, in which case presumably you could add an external battery charger.

NT

[Bob Minchin]

If it rising to 13.5 then it is getting a charge however small from somewhere.

A standard 12v battery is not going to self recover to any more than

12.6 or so with no external influence.

By applying a variable load to the battery once the genset is running you should be able assess the charging current. when the battery sits at

12.6, the current in the load will be about the same as the charging current.

[Dave Plowman (News)]

I've never known anything like that which doesn't. Would be pretty pointless given how little it would cost to do.

[tony sayer]

In article , Dave Liquorice scribeth thus

Yes, ours does...

But its float charged as well just in case !..

[Dave Liquorice]

dropping

battery

Obviously

Hum, further investigation required, I'll admit the exact numbers might be misremembered but I pretty certain of the 12.9 and

13..

Wouldn't the measured terminal voltage drop straight away when the charging voltage is removed? It didn't change between genset running and genset not running... This and seeing under 13 V with the set running is what really makes me think the battery isn't being charged.

[Bob Minchin]

My school boy memory is of a standard lead acid being 2.2v per cell just off charge and quickly dropping to 2v ish giving its all until getting seriously discharged and volts falling off rapidly.

Bob

[Andrew Gabriel]

No, it decays slowly, but I suspect it would decay very quickly with a small load.

It could be either that it was low to start with.

[Fredxxx]

That was my general understanding as well, but in practice the terminal voltage is dependent on charge state.

This PDF gives a good indication. Sadly the figure on page 2 doesn't give the battery temperature, where volts go down with increasing temperature. It also depends on how accurate the battery AH is stated.

It is actually possible, at a small trickle current, that 13.5 volts represents near fully charged.

[Dave Plowman (News)]

No - a lead acid measured with a high impedance voltmeter will give an oddly high reading immediately after charge. There is a term for this I've forgotten. Check it under load.