electrical problem in ignition

[perrocalzones]

I am getting my girlfriends old GS550L back on the road, it's registered in the UK as a 1981 model but we think it may acually be a 1979/1980 US inport. It has an electrical problem that is driving me nuts!

OK, with the kill switch on the bars off - everything is fine, around 12.7v at the battery but as soon as the kill switch is flicked on, the battery immediatly drops to around 4v. Ive disconected the wires to the points and with the kill switch on all OK again. next Ive tried opening the points by sticking in a piece of card between the points, again everything is fine, but as soon as the points (either set) close the battery dies.

if my logic is correct this means there is no dead short to earth before the points, am I right in thinking this? if so what is going on ?? what happens after the points anway?

Ive also tried connecting a car battery which also drained at a slower rate but still held out long enugh to start the bike, once the bike is running all seems ok again with around 13.5 - 14.5v at the battery. I've also tried fitted new points and condenser. to make things more difficult the problem seems to be intermittant and sometimes everything works fine.

any sugestions or advice as to what to check next would be very appreciated as I've run out of ideas. please save my sanity!!](*,)

[Dave8338]

Sounds like your battery is toast. If you have a cell or two that are dead...you'll see a large voltage drop as soon as the coils are live. If you had a deade short, it is unlikely that you could get the bike to run even with another battery connected. My suggestion...clean ALL ( did I say ALL), yes, ALL of your connections, paying special attention to the R/R ground wire, the the ground strap on the battery and the leads to the coils. It seems as though you have corrosion issues in the 25+ year old connectors and a battery, that at best, is half there.

[SPARKSS]

I'll agree with Dave8338's assessment of requiring a new battery......but for a different reason. Because you see good no-load voltage across the battery, it's more likely that the battery is sulphated.......this is a condition that increases the internal resistance of the battery, which greatly reduces it's ability to supply significant power, at nominal 12 volts. Although sometimes (and somewhat) a reversible condition with some batteries, sulphation is a condition which likewise won't allow most chargers to accomplish that.

If you think of the battery as a source of power........and put a crowbar across the terminals, what would limit the short circuit current (and thus the "voltage" across the shorted terminals......the answer is internal resistance - which on a good battery is very low......milliohms. A sulphated battery may have several ohms internal resistance, which, when effectively in series with the external load (you switching the bike on) causes the voltage to be divided between the 2.......you see a mere 4 volts and wonder why. Put another way, instead of the battery being able to supply 100 watts to a load at nominally 12 volts, it may only be able to supply a few watts - at 12 volts....(and really at any other voltage).

[Redman]

Perr,

Your troubleshooting and thought process sounds pretty good.

And I tend to aggree with the advise given by others about the battery. Sounds like the battery does not have the ability to provide much power (and the voltage drops when much of any load presented).

You can veryify that by doing the same test you have been doing, except try turning on the headlight insteasd of closing the ignition points. If you see the battery voltage drop, then you know its the battery, not the ignition.
.

[earlfor]

It sounds very much to me like you have a sulfated battery. Usually, the condition will show 12 volts at the battery terminals, but as soon as you put any load on it, voltage drops to nearly nothing. You have voltage, but no capacity. Its somewhat like having a ten gallon gas tank with one ounce of gas in it. Yeah, its real gas, but there isnt enough to go anywhere. :-)

Methinks you need a new battery.

Earl

[perrocalzones]

thanks guys

I hadn't really suspected the battery as it is only 6 months old and showing a good voltage. Sometimes it's easy to develop tunnel vision and focus on only one possible cause of the problem.

Never come across a sulphated battery before, looks like I was sold a dud! thanks for the advice

[bakalorz]

I hadn't really suspected the battery as it is only 6 months old and showing a good voltage. Sometimes it's easy to develop tunnel vision and focus on only one possible cause of the problem.

Never come across a sulphated battery before, looks like I was sold a dud! thanks for the advice

Batteries will slowly lose their charge in storage, and need to be charged up every month or two. If not kept charged, they become damaged. If it sits on a dealers shelf for a year, it is almost guaranteed to be ruined, since few dealers bother to keep them charged.

The way around that is buy fresher batteries (look at the date codes) or to buy "dry charged" batteries.
Dry charged batteries are sold with no acid in them, it comes in a plastic bottle.

When you get a dry charged battery, you pour the acid in, wait a few hours, and then charge them on a plug in charger for several more hours.

Its a PITA, but you get a guaranteed fresh battery.