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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #1 ·
I know there are a few oldie threads about this but don't think the specifics are the same.

Until last weekend m bike voltmeter was showing 14 to 14.5V at around 4k rpm.

Sunday after a long run and on the way home the voltage dropped to 11.6V at 4k rpm and never maanaged to get it over 12V.

The interesting (not) thing is that after plugging the trickle charger the voltage was still the same 11.7V.
Need to keep in mind that the reading is with ignition and headlight on.
First I thought would be the connection that was not good enough but that has been reviewed and I know it's good.

Yesterday I tested again with the bike cold but the result was the same.

If I connect my digital voltmeter to the battery I see rapidly recovering from 11.7V to over 12.3V so I don't think the battery is damaged.

I have little appetite to spend £200 on a regulator and even would consider building one.
The basis is simple, a diode bridge and a 14 regulator with enough amperage to cope with demand.

What advice do the wise man in here have?

Thank you for reading :cool:

Forgot to mention, it's for the Shadow VT700c '86 and I'm in the UK so parts are harder to get.
 

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1983 Honda vt750 Shadow
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How solid is your 3 yellow wire connection? And you cando this test of the stater=

 
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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #3 ·
Yep @swifty2014 That's the next test.

Now...
Found a canadian guy selling a super dupper mosfet regulator for can$ 180 (including overseas shipping
and a Aliexpress version for $25 :rolleyes:

Some how I don't think we are talking about the same thing....
 

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1983 Honda vt750 Shadow
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This place has been a favorite for many guys, but I don't how much shipping will be.=


 

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Sounds to me like a couple diodes in the rectifier opened up. Each diode that drops out removes 1/2 of the power for the stator phase it serves, and the remaining phases will have to supply all the power. I think rectifiers are much more likely to fail than regulators, but they are generally potted together into a single unit nowadays, so either if either goes, you have to replace both.

Destruction of the stator winding itself, or the connection to it, as Swifty suggested you check out, will have the same effect, and there is a known weak spot in the stator connector.

A trickle charger just delivers a trickle of current, which the battery sucks up power rapidly when it's discharged, so voltage will change slowly. It can be a matter of days to fully charge from a trickle charger, but it's smart to know what your charging RATE is. This is the current in amps, ( milliamps from a trickle charger). You also want to know the state of charge of your battery. If it's a 12 amp-hour battery, and it's 1/2 charged, you'll need to deliver 1 amp for 6 hours, or 100 milliamps for 60 hours to make up the missing 6 amp-hours. I allow about 25% for inefficiency of the charging, so that would be and extra 1.5 amp-hours over what is theorytically required.

I wouldn't be afraid to buy a takeout like this $29 Reg/Rect 86 Honda VT 700 VT700 C Shadow voltage regulator rectifier | eBay. Ebay is loaded with aftermarket Reg/Rects. A unit like this one is a bigger gamble, but folks get do get decent ones and are happy with them. For 82-86 Honda Shadow VT500C VT500F VT700C VT750C Voltage Regulator Rectifier | eBay. I pay with PayPal and ask for a refund if I get a bad one.

I look at the Reg/Rect as a consumable component, like a piston or bearing. Eventually they wear out.
 

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2003 Ace Deluxe
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i second the mosfet from roadster cycle. (Home link above) Home

not only is there a lot of free info on charging systems on the web site but the owner is super helpful responding to questions

installed one of his mosfet regulators on my ACE and am happy
 

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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #8 ·
For what I gathered, Mosfet regulators are required if fitting a lithium battery as the cut off range is more accurate.
HAving said that, I don't think I'll be getting one any time soon if at all.

Aliexpress have quite a fewe under £20, another UK place is sellingg it at less than £30 while CMSL (Continent store) is selling a aftermarket one for £110.

Worst can happen with the £30 one is last for a few months/weeks
By then I will have refurbished the original one.
The fault seems to be a dodgy diode that are usually sold in packs of 10 for £10 / £15.

I know the mosfet ones are less prone to heating. However, that can be worked out by fitting a venting hose from the front of the bike into the regulator.
 

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mosfet can be used on any battery, and if one tries to install LED bulbs or mess with the voltage draw on a honda type charging system you can end up with issues.
the stock system is very basic and its either feeding power to the battery or dumping power as heat.

the mosfet from roadster is more sophisticated and (for my bike) the unit was much larger allowing for better / more heat dissipation.

i had issues with my system, i replaced the stator (no improvement) new regulator (no improvement) new main wiring harness (with improvement) but it wasn't until i finally installed the mosfet regulator that my charging system started working per the manual specs.

the roadster cycle web site is a wealth of info that i found helpful
 

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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #11 ·

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Did you notice that the Reg/Rect from Grandada seems to be missing the black wire to the 5 terminal connector that looks to be present on the original equipment unit?

I'm not sure what that circuit does, but I see it in the schematic posted here: Please HELP 86 Vt700 Complete re-wire Bare Bones Wiring | Honda Shadow Forums Appears to be connected to the ignition circuit. Maybe this is the feedback voltage for the regulator?

Also, the wires seem a lot shorter on the aftermarket than the OEM unit from Ebay, so you may need to extend some of the wires.

Your idea of replacing diodes on your original rectifier seems pretty challenging to me. The device looks to be potted in epoxy. Have you done surgery on something like this before?
 

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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #13 ·
Hi @axman88
Although the connector have 4 wires (2 same colour pairs) the connection to the battery is only 2 wires as below (R/W, Bl).
I'll be using the existing wiring from the existing regulator to the other side so I don't have to dismantle the entire bike as the wires are wrapped together with the wiring harness.

Epoxy resin have a relatively low melting temperature so removing it is not as hard as it seems.
Replacing the diodes are very straightforward and should be done with all 6 so you don't have to do it again soon.
They are dead cheap and anything above 20V 5A will do nicely.
Filling the case again will be done with electrical silicone widely available and perfectly waterproof.

10 X Schottky Diode 60V 5A SB560 Rectifier Diode Rectifier 2050001062512 | eBay

The question lies on the thyristors (the 3 ones with 3rd connection) if I should replace them or not. For this I would need the reference on the casing, often brands will remove it to stop people like me to fix it instead of buying a new one.

Rectangle Slope Schematic Parallel Font
 

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Hi @axman88
Although the connector have 4 wires (2 same colour pairs) the connection to the battery is only 2 wires as below (R/W, Bl).

Epoxy resin have a relatively low melting temperature so removing it is not as hard as it seems.
Replacing the diodes are very straightforward and should be done with all 6 so you don't have to do it again soon.
They are dead cheap and anything above 20V 5A will do nicely.
Filling the case again will be done with electrical silicone widely available and perfectly waterproof.

The question lies on the thyristors (the 3 ones with 3rd connection) if I should replace them or not. For this I would need the reference on the casing, often brands will remove it to stop people like me to fix it instead of buying a new one.
I see what you are saying, the aftermarket regulator must get its reference voltage from the Red/White wires.

It's interesting that each phase has its own thyristor, but they all share the same voltage sensor. Do you think all the thyristors close together, or does the voltage sensor set a threshold and the thyristors trigger based on the AC voltage present on that individual phase?

Do you think that having the lower forward drop of the Schottkies is required, or is this just to waste less power?

I'll be interested in hearing more about the process of surgery on your Rect/Reg, and perhaps learning more about the regulator circuit and how the heat sinking is done. Maybe you will share some pictures when you attack it? The idea of a rebuildable rect/reg is appealing to me. I have a two piece Rectifier / Regulator combination from an older Royal Enfield that has at least one bad diode in the rectifier that I may try to "rectify" myself also, following your lead.

Good Luck!
 

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Discussion Starter · #15 ·
I'll definitely going to be posting the progress.
I know I have a couple other projects on hold that I need to complete and have them working.
Unfortunately the new kitchen and bathrooms refurbs take priority on anything that doesn't prevent the bikes from running. :sneaky:
 

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Discussion Starter · #16 ·
As promised here's an update.

Unfortunately the dismantling of the old regulator is showing to a lot harder than I initially anticipated.
The resin is not a "normal" epoxy but some diabolic compound that refuses to leave.
It softens with heat gun but so does the solder and the wires insulation. :rolleyes:

The worst is, the new regulator is working the same way as the old. Yes I know, should have tried the new one before starting to breakup the original.
Anyoo..

Removed the stator and after cleaning the bit of oil sitting on the magnet. ohmic resistance is sitting within the factory parameters, the cables seem in very good (as you would expect) condition.

So next tracing all the wiring, fuses and whatever is linked to it.

Tempted to put everything all together, do a rain dance and hope for the best, not sure it will work...

Will consider a new £90 stator if I really have to but only IF I have to.
 

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Discussion Starter · #17 · (Edited)
A further update.

Sadly stator is showing a short circuit to earth :cautious:
3.5 ohm resistance on the circuit. (4.1-0.6 line resistance)

Automotive tire Motor vehicle Engineering Gas Measuring instrument


Now on under £20 difference which should I get?
Can't really see much difference between them other than the protective resin on the Electrex while the cheaper one doesn't seem to have it.
Plus the connector is a 2 pieces set while on the cheaper it is only the female connector as required.

Really tempted for the Electrex better looking one.
Rectangle Parallel Font Beige Tints and shades
 
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