850 mk3 Warning Light Assimilator

GDay Chaps,

According to the factory manual, this gadget lights the red ignition warning light when the ignition is switched on, and makes it go out when the engine's started and the charging voltage exceeds that of the battery- meaning the charging system is working ok. I fitted and Al Osborn LED charge monitor in place of the ignition warnning light afew years back but didn't disconnect any of the wires to the assimilator. The charge monitor then told me that when the lights were switched on, the system wasn't charging. Sure enough I found that if I rode with day time headlights for say, 60 miles, the electric start wouldn't, even when I began the day with a fully charged battery and fully operational starter.

I'd always assumed this meant my rotor had lost some magnetism after 40 years, or the rectifier/zeners not doing their job. I'm slowly recommissioning the bike and am now wondering if the warning light assimilator might be at fault too- or if I should just disconnect/remove it. Is there a way of testing these things? Is it needed with an LED charge light?

Many thanks,

crusaderports

An easy test to see if the alternator is charging the battery is to connect for volt meter across the battery terminals and start the engine. If the voltage rises above 13 volts to around 14 volts as you increase the throttle, the system is working. If your charge warning light is on with up to 14 volts at the battery, the assimilator is suspect. If no voltage rise, next check the alternator directly at the two leads for output. It's always possible the zener or rectifier have failed.

crusadersports said:

I fitted and Al Osborn LED charge monitor in place of the ignition warnning light afew years back but didn't disconnect any of the wires to the assimilator.

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As you have removed the assimilator warning lamp then there's no reason to keep the assimilator, it's only purpose (except some Canadian model assimilators) is to switch the charge warning lamp off when it senses alternator output has risen to a certain level and switch it on again when output drops below that level.

GDay chaps,

Thanks illifed, when I get the old girl going again I will do these tests. I'm planning to upgrade to the Sparx 3 phase kit and ditch the o/e rectifier an zenners.

LAB thanks (again!). I assume I can just remove the assimlator and isolate the wires then? Is there any way of actually testing the assimilator all the same? I keep making all these mods, but want to keep all the parts to return to o/e if need be- assuming they are in working order!

Many thanks chaps,

crusadersports

crusadersports said:

I assume I can just remove the assimlator and isolate the wires then?

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Yes.

crusadersports said:

Is there any way of actually testing the assimilator all the same?

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I don't think so (and the manual says nothing)? So either it works-or it doesn't.


Don't overlook the 2MC emergency starting capacitor if it's still fitted, as it can also be the cause of charging problems. Try running with it disconnected (disconnect the red wire from the 2MC. If the two brown/blue wires are removed from the 2MC they must be connected together with a short jumper wire).

GDay LAB, many thanks for all your help.

How can the capacitor affect charging?

I ask as I'm planning to renew this too. Not sure yet whether to get a 2MC equiv or a Boyer powerbox (which apparently includes a built in capacitor so would simplify the wiring). Any thoughts about which would be better? I have a Pazon kit on order and with 3 phase intend to modrnise my electrics. I'd like to keep some sort of capacitor as an emergency start for a drained battery. I managed to leave the ignition on all day once and had plenty of time to reflect on the virtues of capacitors as I sat on the train with a flat battery...

Many thanks,

crusadersports

crusadersports said:

How can the capacitor affect charging?

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The 2MC can sometimes leak current to earth if it becomes faulty, and I wasn't suggesting yours was, but it's something that shouldn't be overlooked when checking a charging problem, or if the battery kept going flat quickly.

As ever LAB, thanks v much for these pointers.

I see what you mean- a faulty capacitor could 'leak' to earth and thus drain a battery- possibly fooling you into thinking that the battery had had it and wouldn't hold a charge. Very interesting!

Thanks again- you're a Gent and a legend.

crusadersports

crusadersports said:

As ever LAB, thanks v much for these pointers.

I see what you mean- a faulty capacitor could 'leak' to earth and thus drain a battery- possibly fooling you into thinking that the battery had had it and wouldn't hold a charge. Very interesting!

Thanks again- you're a Gent and a legend.

crusadersports

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An easy way to check if the battery goes flat quickly...disconnect the red earth wire at the capacitor and see if the battery still goes flat.