880 Selectamatic Dynamo

The place to discuss all matters relating to David Brown Tractors. You will need to register your user name before you can post. If you have already registered could you please make sure that your location details have been completed. Go to My Account in the Main Menu on the left, and then go into "Edit Your Information" and complete your location details. Give the Country (and State/Province if you wish) if outside the U.K. County if within the U.K. Location details helps other members if you need spares, technical advice, or the nearest practical help.

DISCLAIMER -

David Brown Tractor Club Ltd
Forum/website Disclaimer

1. This [forum/website/chat room] and the advice and opinions expressed herein is not a solution for mechanical, electrical, valuations, other problems, breakdowns or issues experienced in relation to the vehicles referenced.

2. If reliance is thought to be placed on any of the information guidance or input provided such information will be expressly confirmed as appropriate to be relied upon.

3. In the absence of any such confirmation no reliance should be suggested or inferred.

4. Members must not disclose information to 3rd parties in anticipation that reliance will be given by non-members.

5. Non-members must not purport to give advice on behalf of David Brown Tractor Club.

6. If you or someone you know is experiencing difficulties or repeated breakdowns you must seek assistance for an appropriately qualified expert who holds themselves out as such.

7. Any comments are free of charge and made or posted on an ex gratia basis. No member or non-member may advertise their professional services

Any user inactive for more than 3 months will automatically be deactivated, please contact admin@dbtc.co.uk if you would like to be reactivated.

Please be aware that your user name and entered location can be seen by all members. We only store information you have entered which is your email address and username, your IP is also stored, we have no access to private passwords.

If you do not agree with your information being stored, please do not register an account, If you wish to unsubscribe at any time please email admin@dbtc.co.uk giving your username.

Amended 27/10/18

Moderators: Segrie61, admin

User avatar
tractorfan
Posts: 90
Joined: Wed Aug 13, 2014 8:25 am
Location: Ceredigion

880 Selectamatic Dynamo

Post by tractorfan » Mon Jul 01, 2019 7:16 pm

I've fitted a new dynamo but now the charging light will only begin to extinguish at 1300rpm and will be fully-extinguished at 1600rpm. Any ideas why this is happening? On the previous dynamo the charging light would have disappeared at 800/900rpm. Many thanks.

blissakpo
Posts: 83
Joined: Tue Jul 17, 2018 7:15 pm
Location: IRAQ

Re: 880 Selectamatic Dynamo

Post by blissakpo » Tue Jul 02, 2019 5:25 pm

Have you tried tightening the fan belt

User avatar
ollek
Posts: 4148
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: 880 Selectamatic Dynamo

Post by ollek » Tue Jul 02, 2019 5:46 pm

Is it possible that you have fritted a dynamo with a bigger belt pulley than the original?

ALANJ
Posts: 68
Joined: Wed Oct 11, 2017 9:13 pm
Location: Co. Durham

Re: 880 Selectamatic Dynamo

Post by ALANJ » Tue Jul 02, 2019 6:58 pm

1- Did you polarise the dynamo after fitment? This should always be done after such replacement.If not done ,suggest you perform this task first. It only takes a minute.
2- Check replacement Dynamo by bridging the D and F terminals and checking output voltage at D with engine running.If voltage low,replace Dynamo.If voltage good check all connections between Dynamo and control box .
3- If connections are good either check control box by substitution ,or voltage input / outputs at D,F, B and ohm test E for good earth/ ground connection.
Good luck.AJK.

User avatar
tractorfan
Posts: 90
Joined: Wed Aug 13, 2014 8:25 am
Location: Ceredigion

Re: 880 Selectamatic Dynamo

Post by tractorfan » Tue Jul 02, 2019 9:14 pm

Thanks for the replies. The fan belt’s at the correct tension and the pulley was removed from the previous dynamo and put onto the new one. The problem with the original dynamo is that it seized while the tractor was working and the first I noticed was that the charging light came on and I saw the smoke from the fan belt running along the stationary pulley. Prior to this all was working.

Actually, I now wonder if the fan belt has worn too much, because there was a lot of smoke coming from it.

I polarised the dynamo and I have a new voltage regulator on order in case, but the regulator was working until the incident.

I’ll keep you posted. Thanks again for the replies - they all help.

User avatar
tractorfan
Posts: 90
Joined: Wed Aug 13, 2014 8:25 am
Location: Ceredigion

Re: 880 Selectamatic Dynamo

Post by tractorfan » Sat Aug 31, 2019 11:56 am

Just to keep you updated, I bought a brand new dynamo and regulator, polarised the dynamo, and fitted them both, but the charging light still won’t extinguish until 1300RPM. I removed an original dynamo from a 770, fitted it to the 880 and all was well. I removed that, re-fitted the new dynamo and the problem reappeared. Could it be the case that new dynamos aren’t very good?

User avatar
ollek
Posts: 4148
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: 880 Selectamatic Dynamo

Post by ollek » Sat Aug 31, 2019 4:10 pm

Some parts (not only dynamos) sold at different outlets on the Internet are of poor quality. Saying that I have to add that if the charging light is swathed off after start up, when you rev the engine to 1300 r/min can be OK. This is if the light will stay off when you lower the revs.

User avatar
tractorfan
Posts: 90
Joined: Wed Aug 13, 2014 8:25 am
Location: Ceredigion

Re: 880 Selectamatic Dynamo

Post by tractorfan » Sat Aug 31, 2019 11:56 pm

Thanks for your reply. When the tractor passes 1300RPM the charging light extinguishes. As soon as the tractor returns to 1300RPM the light comes on again.

This new dynamo is labelled as 11amp. Does this sound correct for the tractor?

User avatar
db2d
Posts: 2241
Joined: Fri Feb 24, 2012 10:01 pm
Location: Monmouthshire

Re: 880 Selectamatic Dynamo

Post by db2d » Sun Sep 01, 2019 1:48 am

The original dynamo would have been a Lucas 11amp C40A but a
Lucas 40T 22amp was also used.

User avatar
rid54
Posts: 210
Joined: Mon Oct 13, 2014 8:20 am
Location: Vallentuna, Sweden

Re: 880 Selectamatic Dynamo

Post by rid54 » Sun Sep 01, 2019 11:32 am

I am fairly convinced you should be able to measure the output voltage of the dynamo as the engine is idling (approx 700 rpm, I think) and see what happens when you increase revs. Normally, one would expect sligthly below 12 V (rising with the engine speed) until engine reaches 800-900 rpm, then the chargiing should begin and the voltage should be around 14 V. Once the regulator cuts in the charging, dynamo output is equal to system (battery) voltage. When engine speed drops, the cut-out part of the regulator should decouple the dynamo to prevent back-current from the battery (and the warning light will be lit).

What is the system voltage once the dynamo starts charging?
I suppose it is impossible that a 6 V dynamo might have been erroneously delivered to you.

User avatar
tractorfan
Posts: 90
Joined: Wed Aug 13, 2014 8:25 am
Location: Ceredigion

Re: 880 Selectamatic Dynamo

Post by tractorfan » Sun Apr 05, 2020 8:27 pm

Hello all,

I'm now looking at this issue again, and am now convinced that the dynamo's faulty. I bridged the D and F terminals and measured the output at D to be 0.4v

This dynamo is a Prestolite.

Thank you.

User avatar
rid54
Posts: 210
Joined: Mon Oct 13, 2014 8:20 am
Location: Vallentuna, Sweden

Re: 880 Selectamatic Dynamo

Post by rid54 » Sun Apr 05, 2020 9:49 pm

I think one would expect the field winding and the armature both to have one end connected to the dynamo case = negative pole = "earth". Field current is fed to the F or DF terminal and at D+ the output is collected. Field connector and D+ (or just D) should have continuity to ground/case/earth, measured with a mutlimeter at resistance range. Field might show a few Ohms, but armature should have very low resistance. Any cables at the terminals should be disconnected when measuring. To me this situation seems like there is no field current and the dynamo output is due to residual magnetism only.

User avatar
cobbadog
Posts: 874
Joined: Tue Oct 11, 2011 6:18 am
Location: beautiful Coopernook NSW. near Taree. NSW. Australia

Re: 880 Selectamatic Dynamo

Post by cobbadog » Mon Apr 06, 2020 12:42 pm

It does sound like a faulty dynamo for sure.

Gard
Posts: 307
Joined: Sun Apr 06, 2008 2:25 pm
Location: Fairfax Vermont USA

Re: 880 Selectamatic Dynamo

Post by Gard » Tue Apr 07, 2020 12:38 pm

You may be able to adjust the voltage output with an adjusting screw inside the voltage regulator. Not sure what you have. I have Lucas service manual that details the measurements and adjustments, I can send a copy if you PM me. It might be informative even if your regulator is not lucus. My guess would be the dynamo is OK if it works at higher RPM.

User avatar
rid54
Posts: 210
Joined: Mon Oct 13, 2014 8:20 am
Location: Vallentuna, Sweden

Re: 880 Selectamatic Dynamo

Post by rid54 » Tue Apr 07, 2020 4:11 pm

I would strongly suggest measuring the dynamo windings, and also ascertaining that it does not have any kind of irregular connection system (being of another brand than the original, apparently). If the armature or the field windings do not have continuity, the dynamo is defective. If the windings are OK but it still does not work, the problem is either in the regulator, the connecting cables or the brushes (or the earthing, albeit far-fetched). A quick test may be to run the engine (and the dynamo) with D/D+ connected to a multimeter at a 20 V range and then for a very short while connect the F connector to battery + and see if the voltage increases. If this test "works", the regulator is the prime suspect.

Post Reply

Who is online

Users browsing this forum: No registered users and 19 guests