Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Woe unto you that bought the first model year of a major remake, perhaps this section can help address any 2014 and later model Ural "imperfections". Here's a special section for folks with the latest rigs to discuss 2014 and later model-related topics such fuel injection, 3-wheel disc brakes, hydraulic steering dampers, spin-on oil filters and other anomalies that don't belong on true Russsian motorcycle ;-P We've gone from using big hammers and greasy wrenches to needing computers and Ouija boards in order to fix our rigs.
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Eric N
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Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Eric N » Sun Feb 16, 2020 6:15 pm

I've had a sense my alternator's kinda iffy, but yesterday plugged a meter across the battery to test how accurate the LCD display on the speedometer is, seems to match. I know that's not the perfect way to test alternator output, but I think it's close enough.

Went to run errands and watched the output was all over the place. At 70mph driving down the highway I had a stint where it was just staying at 12.4V.

Sometimes it will climb to 13.7, I've never seen it over 14V.

I'm thinking the regulator might be a problem, but was wondering if anyone else has run into the same thing. I'm not the best at alternator stuff, willing to learn, and it doesn't feel like it should be doing that. Instinct is at 3,000 rpm I should have 14.something and keeping it pretty steady unless there's something else going on.

I'm going to recheck connections, could be something just wiggled loose that I missed yesterday, but any thoughts on the culprit?

Has anyone swapped out a regulator on a Denso?
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Re: Denso voltage fluctuates at 3,000 rpm? 12.4V - 13.7?

Post by Lofty » Sun Feb 16, 2020 6:23 pm

Eric, I had a similar issue with my Suzuki. The charging voltage fluctuated significantly at any engine speed above warm idle, when it should have been between 13.9v to 14.3v (based on its observed function from new). I was seeing spikes above 15.0 volts on the BlueSea digital voltmeter that I had installed on the bike.

The culprit was determined to be the OEM regulator/rectifier. I replaced it with a well-regarded and not-inexpensive MOSFET unit. The charging voltage is now rock steady, no matter how many accessories are powered at the time (within the limits of the available wattage, natch).

The one qualification that I'd mention here is that the Suzuki is equipped with a stator, and not an alternator as is the Ural. Perhaps having the former made it easier to isolate the R/R as the problem? Just a thought.

Best of luck with finding a solution here.

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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Eric N » Sun Feb 16, 2020 8:07 pm

Excellent writeup by Ernie Franke http://www.russianiron.com/eafranke_ura ... -0600).pdf

I've had to replace rectifier/ regulators on two Hondas and an Enfield. It's likely the culprit with the Denso. Just seemed odd, bikes that had the repair were way older, way more miles, but sometimes something just fries.
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Eric N » Sun Feb 16, 2020 9:06 pm

Ordered $24 part on eBay, worth a shot https://www.ebay.com/itm/Voltage-Regula ... item342084


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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by RC20 » Sun Feb 16, 2020 9:32 pm

Anything over 2000 rpm and you should have 14.5. Probably 1500 but 2000 is safe. Initial startup idle of 1200 or so you will get 13.5.

Usual problems are the 6 pack of diodes in the alternator that turn it from AC to DC.

The other is the regulator. Haven't worked on a Ural type, I think its all internal regulator but?????

Electronics are goofy and you are seeing a breakdown/heal thing which is not uncommon. They can last forever or fail on first fire up.

Frankly I liked the stuff with the external regulator as you could then test the field and see if that was ok inside.

Those had a 6 pack of diodes inside.

If I had my choice I would drop the voltage down to 13.5 or so and get more life out of the battery which I could do on an external regulator (assume it was adjustable type)

I was forced into it on a car in Puerto Rico, damned thing was charging the battery at 16-18 volts it was hot there as well. We found out on a long trip, normally it ran short runs in town and not long enough to be an issue. New battery to start with as it killed the old one.

I did not have the manual so tried to get a new regulator. Getting through to Puerto Rican parts guys who did not care if they sold you a part or not was impossible.

So I took the cover off and made my guess, got it right and toned it down to normal. Bless digital meters, you really know what you are getting and seeing is valid and can deal with the rest.
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Mr Wazzock » Mon Feb 17, 2020 1:29 pm

Very interesting!

I like the PDF. Note how the table indicates how fast you have to be going to get close to the supposed maximum output.

But be aware also, the LCD Voltmeter in the speedo is on the end of a bunch of wiring, fuses and connectors, don't know about yours but if it's like my bike the Voltage can be down maybe 1 Volt or more if I measure it anywhere except directly at the battery. Hence I wouldn't be surprised if the LCD Voltmeter is getting a similar drop. This is also a known problem on cars that have a Voltmeter function on the dash in some form or other, so much so that the readings cannot be trusted to be too accurate.

I have a plug-in cigar lighter socket style digital Votmeter I can use, yet still is most meaningful if the socket is straight off the battery.
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Wildhorse Cafe » Mon Feb 17, 2020 8:39 pm

It could also be the battery with an internal intermitten short or a dead cell. They can cause unusal readings.
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Eric N » Mon Feb 17, 2020 9:19 pm

Wildhorse Cafe wrote:
Mon Feb 17, 2020 8:39 pm
It could also be the battery with an internal intermitten short or a dead cell. They can cause unusal readings.
The battery shows a steady 12.4V , not sure how the alternator load to the battery would fluctuate with a bad cell. Although I am taking readings at the battery terminals, even with a bad battery I would expect the alternator output to the battery to stay close to 14V.

Can you help me understand how the battery would impact? How would it alter the power going to the battery?
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Wildhorse Cafe » Mon Feb 17, 2020 10:25 pm

Measuring at the alternator is electrically the same as measuring across the battery, assuming there are no loose cable issues, the internal battery resistance can load down your system or act as an near open load. Sometimes a battery with sort or near short can cause your. engine to load down and run really crappy because of a combined mechanical and electrical load. A open or light load will just read as a high voltage reading. But a battery can also become eradic intermittentlly loading and unloading your altenator. If you have access to a know good battery jumper it to your bike and observe, The voltage will probley be low at idle come up to between 13.8 to 14.4 at speed.

It's simple, a discharged battery has low internal resistance, a charged battery has high internal resistance and most batteries are inbetween.
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Peter Pan » Mon Feb 17, 2020 11:58 pm

one thing: a deeply discharged battery takes a lot of riding to get back to normal behaviour. My Sophie was dismantled for 7 month. Short distance riding for a month did not charge the battery enough and I feared to have to change it (about 12.1-12,5V and fast discharged). One 300km ride and all is back to normal. Jim Pettiti's Olympic battery definitely was worth its bucks. 6 1/2 years now.
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by RC20 » Tue Feb 18, 2020 4:02 pm

Wildhorse Cafe wrote:
Mon Feb 17, 2020 8:39 pm
It could also be the battery with an internal intermitten short or a dead cell. They can cause unusal readings.
Can't happen, wrong info.

Batteries are series units. Dead cell and no voltage at all.

Same thing with intermittent, once it breaks it stays broke.

If it shorts it blows up (ask me how I know)

You can have a weak battery for various reasons but you will not have one as you have described twice now.

Resistance alone does not detail a battery condition. The system that use that have a ref battery, they then assess a new one and very slight increases or decrease will indicate condition. It all has to be logged and put into the device. That is why the cheap field devices do not work.
Last edited by RC20 on Tue Feb 18, 2020 4:08 pm, edited 1 time in total.
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Formerly Owned: ( various rides on others)
Honda 90
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1 x CB700 SC ala Shaft Drive Nighthawk S (RC20 is the actual in house production Model)
1 x R80GS (ok to start with, learned to love it for what it was)
1 x CB450K

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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by RC20 » Tue Feb 18, 2020 4:05 pm

Peter Pan wrote:
Mon Feb 17, 2020 11:58 pm
one thing: a deeply discharged battery takes a lot of riding to get back to normal behaviour. My Sophie was dismantled for 7 month. Short distance riding for a month did not charge the battery enough and I feared to have to change it (about 12.1-12,5V and fast discharged). One 300km ride and all is back to normal. Jim Pettiti's Olympic battery definitely was worth its bucks. 6 1/2 years now.
That is spot on. Not all will recover but if its a good battery to start with then getting the chemistry stirred up for long enough will restore it.

The key is what is called and equalize. A charge that puts 14.5 volts out for some hours (we used 12 to 24 but not required)

Even a two hour run is a big help. Series of regular one hour runs works.

Just sitting and on tenders is not the way to a long battery life. They need that boost of a good 14.5 volts into them.
Fear No Gravel
Formerly Owned: ( various rides on others)
Honda 90
2 x CB750K (one a true Japan Model flown to Hawaii by a P3 Orion Sub Patrol Aircraft!)
1 x CB700 SC ala Shaft Drive Nighthawk S (RC20 is the actual in house production Model)
1 x R80GS (ok to start with, learned to love it for what it was)
1 x CB450K

Current:
1 x 2019 cT Terracotta

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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Wildhorse Cafe » Tue Feb 18, 2020 4:24 pm

RC20 wrote:
Tue Feb 18, 2020 4:02 pm
Wildhorse Cafe wrote:
Mon Feb 17, 2020 8:39 pm
It could also be the battery with an internal intermitten short or a dead cell. They can cause unusal readings.
Can't happen, wrong info.

Batteries are series units. Dead cell and no voltage at all.

Same thing with intermittent, once it breaks it stays broke.

If it shorts it blows up (ask me how I know)

You can have a weak battery for various reasons but you will not have one as you have described twice now.

Resistance alone does not detail a battery condition. The system that use that have a ref battery, they then assess a new one and very slight increases or decrease will indicate condition. It all has to be logged and put into the device. That is why the cheap field devices do not work.
True my mistake, a dead cell will be a short low resistance on that one cell. But an open cell will read as max voltage across the entire battery when charging.
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2013 Black Retro, Chernaya Krasota, formally known as, my name is nobody.

When you set out on your journey to Ithaca
pray the road is long , full of adventure, full of knowledge
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Ithaca has given you the beautiful voyage

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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by Eric N » Tue Feb 18, 2020 8:25 pm

Bike wouldn't start this morning, rode it a couple hours this weekend. I've plugged the battery into a charger and will get it tested to rule it out. Dealer also thinks battery is more likely, this is the 2nd battery in two years, dunno.

Ordered a Battery Tender Li battery just out of curiosity and will put that in to see. I'm usually a AGM kinda guy, but this looked interesting (much cheaper elsewhere, their MSRP is kinda high). If current battery tests fine, the battery in my Retro is 7 years old, Cross Country is 6 years old and I'll keep the AGM as a spare for one of them. http://www.batterytender.com/Battery-Te ... -Smart-BMS
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Re: Denso voltage fluctuates at 3,000+ rpm? 12.4V - 13.7?

Post by RC20 » Thu Feb 20, 2020 5:19 pm

Is this the 2018?

You can shift the display into voltage mode to see what is going on if so.
Fear No Gravel
Formerly Owned: ( various rides on others)
Honda 90
2 x CB750K (one a true Japan Model flown to Hawaii by a P3 Orion Sub Patrol Aircraft!)
1 x CB700 SC ala Shaft Drive Nighthawk S (RC20 is the actual in house production Model)
1 x R80GS (ok to start with, learned to love it for what it was)
1 x CB450K

Current:
1 x 2019 cT Terracotta

What I Did (I quit June 2 , 2019)
Mechanic/Technician/Engineer: Electro Mechanical Systems

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