How hot should my dynastart run?

[Tam Lin]

I have just replaced the dynastart on my Volvo MD2B as the old one burnt out. After running the engine for about ten minutes the dynastart is quite hot, in fact you can't leave your hand on it. Now I don't want my new unit to go the same way as my old one so the question is, how hot should it run? The batteries are new and charged to 12.6/7 volts. Today I tried running the engine with just one battery connected with the same result. The engine also has an alternator fitted. Could someone please tell me that I am worrying about nothing and it is fine or alternatively give me some pointers on where to go next. When Amazon deliver my book on boat electrics I may be able to sort this out for myself but in the meantime the combined knowledge of the forum would be appreciated!

 

[VicS]

Not right I would think.

With an alternator fitted just what is the dynastart doing. If the alternator is totally replacing the generating function of the dynastart I not expect it to get significantly warm, just slightly maybe.

even if under heavy load I'm not sure Id expect it to get that hot that quickly. how hot does the alternator get .... how hot is your car alternator after 10 minutes.

I fear some serious checking by an experienced electrician may be in order.


not a problem with its starting function I suppose ...remaining energised.

will look at the wiring diag tomorrow .....

 

[Niander]

Sounds too hot ...but you could just rig it as a starter motor

 

[sailorman]

I have just replaced the dynastart on my Volvo MD2B as the old one burnt out. After running the engine for about ten minutes the dynastart is quite hot, in fact you can't leave your hand on it. Now I don't want my new unit to go the same way as my old one so the question is, how hot should it run? The batteries are new and charged to 12.6/7 volts. Today I tried running the engine with just one battery connected with the same result. The engine also has an alternator fitted. Could someone please tell me that I am worrying about nothing and it is fine or alternatively give me some pointers on where to go next. When Amazon deliver my book on boat electrics I may be able to sort this out for myself but in the meantime the combined knowledge of the forum would be appreciated!

what is the amperage out put, it will get hot 8 amp @ 12v + 100 watts if my maths is correct. a 100 watt bulb is too hot to touch

 

[causeway]

The one on my md7a was never 'very' warm.

 

[William_H]

With an alternator fitted as said one would expect you would disconnect the charging aspect of the dynastart. However with an alternator fitted we might expect a charging voltage closer to 14v. So perhaps it is a simple case that the alternator is not charging leaving it all to the dynamo of the dynastart. Try disconnecting somne of the lighter wires from the dynastart while watching amp meter or volt meter to determine which are involved with charging. These could be left disconnected. Then track down what the alternator is doing or not doing. Dynastart should be barely warm if not charging. good luck olewill

 

[VicS]

what is the amperage out put, it will get hot 8 amp @ 12v + 100 watts if my maths is correct. a 100 watt bulb is too hot to touch

Your arithmetic is correct but your physics is not.

In your example the electrical power output is 100 watts, which coulbe converted into that much heat energy in an external circuit.

Heat produced in the alternator would be zero if it was 100% efficient at converting the mechanical energy input into electrical energy. It's not of course. The heat produced is the difference between 100% and its actual efficiency.

Curses upon you for making me deliver a physics lesson at 6 am in the morning

 

[fergie_mac66]

The last dynastart I had was on a Catalac had a dynastart for the starting batteries and the alternator went to the domestic/navlights batteries , 4bat's total.. the dynastart had a switching unit which made it 24v start 12v charge, doubt that yours is like that but if it is and the switching not working Im sure the issue would cause problems

 

[Tam Lin]

Thanks everyone for your suggestions. It seems like things are not quite right. VicS you ask some pertinent questions - why is the dynastart still connected if there is an alternator? Don't know, wasn't me what done it! The alternator gets slightly warm, if it was water you could say luke warm, certainly not enough to cause concern. I will try feeling my car alternator this afternoon when I go out.
I thought about disconnecting the charging side of the dynastart and seeing what happened but I don't know if that is safe to do. There are four small wires which come off the side of the unit, according to the wiring diagram three of them go to the regulator and one to Earth. As the boat is on a swinging mooring I won't be able to go out for a couple of days (grandson's birthday party and it's a bit windy!) but will try running the engine with the charging side disconnected. If the alternator is working I shouldn't need the dynastart for charging and could just use it as a starter motor. Of course if the alternator isn't working then I've got another problem!
Thanks again everyone.

 

[pampas]

If I remember correctly the dynastart should regulate around 13.4 volts . In your case I would connect to its own dedicated starter battery so that the Alt voltage will not interfere with the regulator voltage coil operation. Doing this I would expect the dynostart to run warm when on full load, bearing in mind cooling air is minimal. You may have a fault in the regualor its self allowing starter current to flow when running, this woulds cause the symptoms that you have described.

 

[fergie_mac66]

If I remember correctly the dynastart should regulate around 13.4 volts . In your case I would connect to its own dedicated starter battery so that the Alt voltage will not interfere with the regulator voltage coil operation. Doing this I would expect the dynostart to run warm when on full load, bearing in mind cooling air is minimal. You may have a fault in the regualor its self allowing starter current to flow when running, this woulds cause the symptoms that you have described.

+1 if dyno and alt connected to same battery and supposed to be connected to different batteries that would cause probs careful with connections of the alt' As they if they are not connected properly when the engine is running damage can result
edit: you need to be sure all the connections are made as they were on the original

 

[RogerLS]

I had the combo of dynastart and alternator once. It was disastrous. The dynastart puts out something like 40 volts and the control relays switch the current on and off many times a second giving something like 12 volts on average at the battery. The high intermittent voltage then fries either the diodes or the control pack or both in the alternator. In our case we got maximum charge rate and boiled the batteries - very nasty smell in the cabin!!.
We cured the problem by disconnecting the windings of the dynastart - connecting them only in the start mode. This worked for a summer; after which we replaced the engine.
I cannot remember the connections exactly. This happened in 2000.

 

[neil_s]

I guess your dynastart, being on a Volvo engine, will be the Bosch unit. I have the manual for the Siba dynastart which may well be representative - it says that the maximum field current is 3-4 Amps. If your machine is getting hot, maybe the control box is not regulating correctly. Perhaps you could check that the relay contacts are clean. You could also check the battery voltage on charge to make sure it's not going too high.

 

[oldharry]

Definitely should not be getting that hot that quickly, and if the previous one burnt out then this one looks to be going that way quickly too, which means it is not the Dynastart that is faulty.

Two things come to mind: as suggested above paralleling two generating sources is not good, and will cause all kinds of problems as they each try to sense the charge state of the battery they are charging. Second, the usual cause of problems with Dynastarts is the mechanical control boxes, which almost invariably cause problems sooner or later particularly if they get at all wet.

A simple test of the Bosch unit is as follows: does the voltage rise above 13 volts at the battery when the engine is running? (with the alternator disconnected) If not, remove the D+ and the DF connection. Also remove the belt. Connect a wire to DF, and a multimeter connected across D+ to E. Now using the starter key spin up to full speed, release the key and earth the DF wire. If the meter jumps to 16v or more, and the dynastart slows quickly, it is OK and the trouble is the control box or the wiring. Solid state controllers are available which are much more efficient, from around £75.

These units are only designed to give around 8 amps. A faulty control box can cause it to push more than twice this, which causes the field coils to overheat and burn out. If yours is quickly overheating, this could be the cause. You can safely disconnect the DF and D+ connections and use it simply as a starter. There's no solid state stuff inside to get damaged as there is in the Alternator!

 

[VicS]

Not right I would think.

With an alternator fitted just what is the dynastart doing. If the alternator is totally replacing the generating function of the dynastart I not expect it to get significantly warm, just slightly maybe.


will look at the wiring diag tomorrow .....

The VP manual shows the dynastart charging the engine battery and the alternator charging the domestic battery quite independently when both are fitted.

It the light of what has been said in other posts you should make sure this is how the two are used. Obvously it rules out switching systems that might combine the two circuits.

With only one battery or with a system in which engine electrics and domestic circuits are not separate I guess it would be necessary to disable and disconnect the dynamo function of the dynastart and use the alternator only.

As suggested check the output from the dynastart.. If it's the original control box ITYWF that it is an electro mechanical system similar to that used in cars when they had dynamos, but incorporating the solenoid for the starter function... it could be malfunctioning causing the dynastart to run at max output all the time. ( later control boxes I think may be electronic and they have a separate solenoid for the starter function.)

In view of the speed with which it overheats I think I would begin by checking that the solenoid ( or even the start button) is not sticking and energising the starter function all the time.

 

[fergie_mac66]

I know nothing about the arrangement on a volvo in fact dont no nothing but on our cat The dynastart was feeding 2 batteries on the start side and the alt' was feeding 2 batteries on the domestic. The dynastart had a switch box that made the 2 starting batteries 24v start and 12v charge