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Voltage Drop Question?

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Pigford View Drop Down
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    Posted: 27 Jul 2017 at 16:58
My latest project (1980 Guzzi 850) is being a pain.

I have just fitted a h/d battery (replacing an older decent one) and still have a voltage drop issue when starting the bike.

The wiring is okay - there is a good +12v across the whole system including complete spark system with ignition on.

When the starter (Valeo) is operated it spins very nicely, but the voltage to the ignition (Lucas Rita) drops to just 10v   

Lucas Rita works well when the bike decides to catch - I believe the RITA needs a decent 12v to work properly due to the long dwell period required! When running it's all good - plugs are okay - it's just the voltage drop on turning engine over causing a problem.... even tried a relay to get power direct from battery to Rita, no difference as still only about 10v left due to heavy starter draw!!!

Any idea's why the voltage drops so much - the new battery has 300CCA power and is fully charged - problem happened on older 190CCA battery too!
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ranton_rambler View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ranton_rambler Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jul 2017 at 17:19
Have you got decent big leads from the battery to the starter, and are all the connections good. I'd need to look at mine to check how the starter earths back, but maybe paint or rust on an earth connection?
I've got a RITA ignition on a SP1000 using a lawnmower battery and have no starting issues.
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jul 2017 at 18:25
I had the same with mu SPIII, and put a smaller 20AH Westco battery in, had no problems with the Rita.
 
How are you measuring the voltage?
Brian.

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Pigford View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pigford Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jul 2017 at 14:45
Earths are good - big cables & clean connections......

To measure voltage to Rita, I'm just disconnecting 3 pin plug & sticking me probe into supply. It measures 12.5v with ign switch on and drops to 10v when starter is cranking!

Wondered if solenoid is dirty or even starter brushes as bikes been sat for 9 yrs, even if it does spin engine over nicely???
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jul 2017 at 16:21
Can you just check the voltage across the battery terminals when cranking?
 
Even if the solenoid was dirty, it wouldn't affect the voltage there. And stop worrying about the starter motor, if it works it's fine.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2017 at 10:51
12.5 volts is very low for a charged battery - should be at least 12.7. I would suspect a poor connection somewhere along the line. Have you tried connecting the RITA direct to the battery to eliminate the intervening wiring?
Ian
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2017 at 18:34
We need to know the voltage across the battery terminals first to know if there is any drop in the feed to the Rita.
If indeed there is only 12.5v there, then it is likely the bike is not charging the battery fully, hence the drop when cranking. Though batteries do drop considerable under cranking conditions.
Brian.

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Pigford View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pigford Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2017 at 19:17
Sorry having NOT replied - got one of my Granddaughters staying for a few days!!!

Hope to have a check this weekend to report back......

Thank you for the input gents
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pigford Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug 2017 at 17:11
After asking one of the garage lads at work (he has a BSA but works on trucks all day), he reckons when the battery is turning the starter, a reading of 10v would be about right at the battery.

Anyhow, I've now removed the LUCAS RITA system - replaced the whole distributor with a decent 2nd hand unit (from Spain for £75 delivered)and she fires up straight away now!

I replaced the complete dizzy coz I didn't have any of the points stuff (adv/retard weights are not present for RITA), so it was best way to get it complete!

Bit of a cop-out, but an easy fix....... sorry I don't have a final answer to my original problem. My new battery actually shows 12.75v so it's a good'un!

Many thanx for all your help & advice chaps!!!
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