Dyanstart Data - the need for an Alternator on a Volvo MD1b

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ump010

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www.yachtelectricalservices.co.uk
Thought this might be interesting to others who have a Volvo MD1b or
similar with a Dynastart.

Measured the starting and charging current (temp around 10 deg C) as
follows:

Starting - first 1 - 2 seconds around 180A, thereafter around 90 amps.

Charging - first minute 11 amp, therafter dropping to 5 amps after 5
minutes.

As you can see a Dynastart can only just cope with keeping it's
starting battery charged, and then not fully. It cannot cope with
domestic batteries as well.

The solution, fit an alternator, that's what I'm going to do. Has
anyone done this already? I'm sure someone has! If anyone can supply
details, pics if possible, of the mounting brackets they have made/used
I would be grateful.

Interested in your comments.
 
I have just acquired a boat engined by a Volvo MD1 with Dynastart. Someone about 10 years ago added an S.E.V. Marshall 35 amp alternator, to which I have just fitted a Sterling Universal Advanced Digital Regulator.
I have yet to run the engine with this set up.I can photograph the alternator mounting arrangements and supply a photocopy of the, almost illegible, hand-drawn wiring diagram.
PM if you are interested
 
Have an MD2 with Dynastart and a 60 amp alternator as well; the Dynastart is used only as a starter motor.

This is a very common (I would say - near universal) modification, involving a pulley bolted to the flywheel driving the alternator fitted above it, leaving the Dynastart belts in place.

Did it 20 years ago and have not regretted it.
 
Fitting an alternator to an MD1

I fitted one to an MDII not a I so this comment may be misleading.
I presume you will still use the dynastart for starting otherwise you have to get a starting system as well.
I took the advice of my engineering shop.
!. Find your alternator - preferably 2 of the same type from your local dead car place and make sure they work.
2. Design a pulley system fitting on the front of the MDI flywheel. There ought to be some useful holes on the front of the flywheel. I suggesnt you make the pulley diameter twice that of the alternator pulley but a higher ratio may be preferable -and practicable?
3. Make up a bracket to hold the alternator out of plywood/glue/bits of softwood.
4. Check out the bracket for everything you can think of :- adjusting belt tension, fitting in engine bay, alignment of belt etc.etc..
There should be suitable attachment points on the engine to take the bracket and tensioner.
5. When you fit the alternator do disconnect the charging side of the dynastart. The voltage control of the dyastart is a pair of on/off relays so you get constant cycling of voltage between nothing and a hell of a lot. This will wreck your alternator regulator and/or diode stack. How do you think I know this?

You may need to rebuild your engine housing.
You will also need to think carefully about charging control/ 1 or 2 batteries, use of split charge diodes or relay control (forgotten the name of the charging relay needed.
A big alternator does take a lot of power and also its drive belt carries a big load and can wear. Its unwise to be too greedy.

Before I put an alternator on my MDII I was always running down my batteries. Your measurements make a lot of sense of my experience.

5. Take plans for pulley and mock up bracket to your local engineer for fabrication
 
Comments

The dynastart has no problem keeping up with the starter load.

If you churn for 5 seconds to start you use about 0.175 Ah (2 sec at 180A, 3 sec at 90A).

1 minute running at 11A charge will replace 0.183Ah, job done!

The problem is the output and regulation of dynamos, which is why you end up with a trickle charge thereafter.

You're right, you need an alternator.
 
Just to balance the books so to speak, I have never had any problem with the dynastart on my MD2B. It has always coped with my electrical demands (vhf, gps,echo. log, lights etc., but no fridge or other high consumption items). I have to say that I do a fair amount of motorsailing though.
I did put a lucas alternator on my Vire 6 engined Macwester Rowan, which worked well, disabling the dynastart charging side. However the drag of the alternator was sufficient to stop the starting side of the d/s in it's tracks. Cured by disabling the alternator until the engine started. This worked well for several years until I sold the boat.
Cheers, Dave
 
The current drop after 5 mins may be because you have fully charged batteries. But the main point of my post is to say try a new voltage regulator for the Dynastart. I got one from LSUK last year and it made a huge difference to charging performance from the Dynastart. Cost around £40-50 I think.
 
My MD1B had an alternator fitted by the previous owner. The alternator is secured by brackets bolted to the cylinder block (where the hand-start bolts on) and also sharing the adjuster bolt with the Dynastart. I could take some pics if you wish - just send me your email address. There are pitfalls - this summer one of the alternator brackets sheared through as I was about to motor into Whitehaven marina!!
 
There is no doubt that an alternator has the capacity to charge with more current and also supply more power to the loads however...
Your dynastart charging beginning current of 11Amps which drops to 5 indicates that that is all the battery will absorb.
If you had a service battery in paralell ie switched or with a VSR you would find that the dynastart generator would deliver 11Amps maybe a little more to the combination of batteries. This would continue for longer depending on the charge state of the service battery and eventually drop down to around but more than 5 amps.

The point I am making is that with battery charging the current in is dictated by the voltage presented (strived for usually 14 volts) the discharge state of the battery and the size of the battery.
The current rating of the alternator or dynastart is a max capacity and then not at 14 volts but more like 12volts. In other words the only time you can get max current from an alternator is usually with high loads ie fridge and lights not with battery charging.

The exception being if you fit a smart regulator which gets more current into the battery by increasing the voltage.

What I am trying to say is that the dynastart may well suit your needs for charging if it is in good condition and the regulator adjusted correctly even with an extra services battery connected in paralell with the engine battery. good luck olewill
 
Watch ou with dynastarts loading batteries over 65 amps. They tend to run hot and burn their ankers.

My solution is using my dynastart on a 50 amps battery and using this battery just for starting never had a problem. Next I got a 190amps deep cicle on a 50 amps alternator separated from the starting system (with a bridge for eventualities). I only put current on the alternators fields after the engine runs.
 
I've got a dynostart charging a house and starter battery. The batteries are linked by a VSR. I appreciate that the output is only 170w but that will recharge the start battery in a few minutes and the top up the house unit for as long as the engine runs. I've also got a 20w solar panel which will provide the rest of my power.
For the sort of setup I have, I'm expecting this to be more than adequate. I wouldn't think that any boats with a Dynastart would have heavy consumers such as fridge or radar so can't see why you would need an alternator.
I have no room to fit one anyway so have to make do with what I've got.
 
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From the figures you have measured, I don't see how you reach the conclusion that the dynastart will barely cope with recharging the starter battery. It appears that it will be recharged in 10 times the time it takes to start the engine. If you say 30 seconds, it will be recharged in 5 mins. Which is exactly what your figures show!

ump010 said:
Thought this might be interesting to others who have a Volvo MD1b or
similar with a Dynastart.

Measured the starting and charging current (temp around 10 deg C) as
follows:

Starting - first 1 - 2 seconds around 180A, thereafter around 90 amps.

Charging - first minute 11 amp, therafter dropping to 5 amps after 5
minutes.

As you can see a Dynastart can only just cope with keeping it's
starting battery charged, and then not fully. It cannot cope with
domestic batteries as well.

The solution, fit an alternator, that's what I'm going to do. Has
anyone done this already? I'm sure someone has! If anyone can supply
details, pics if possible, of the mounting brackets they have made/used
I would be grateful.

Interested in your comments.
Click to expand...
 
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From my experience with an, admitedly rather tired, MD1, I have to wonder if the poor thing will have enough umph left to push the boat.

My alternator has a maximum output of 55amps. At 14v, that's 770w. Assuming 50% efficiency, it'll absorb 1550w, or 2HP. OK, that's the worst case, and would only happen for a few minutes even if you've run the batteries right down, but the MD1 only managed 7HP when new, and most of them will be 40+ years old, so I'd guess that they'd be doing well to manage 5HP.

OK, that's strictly a back of envelope calculation, but it does suggest that if the alternator's working hard, there may not be a lot left to punch a tide.
 
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