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fordens avatar image
fordens asked

Can an Orion DC/DC 30 damage the alternator?

Hi all,

just had a full BMS system installed on my canal boat, Distributors and Lynx, controlling a bank of 2 x 330ah lithium batteries. My engine has 2 alternators about 60a each so I hooked them up on one Orion non-isolated each, one directly from alternator, second in parallel with start battery.

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I did not really monitor the temperatures and current from start, but after running the engine for a couple of hours at idle I saw that the start battery is discharging to 11.5v. I disconnected the Orion and found that the alternator was dead. No output at all, while there was some current going into the system at the beginning.

the second alternator was having voltage jumps from 17.5v to 8v then 14v and so on, within seconds, so no charge going into the BMS.

this is a pre-owned boat so I cannot guaranty that the alternators were not already very much tired, but my question is: could the Orions damage or overheat the alternators (that may be were at the end of their lifecycle) and do an irreversible damage to them? Thanks

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3 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

It's possible (but not likely) you exceeded the maximum power output of the alternator with a combined load of the Orion, the battery connected to the alternator and any local loads. Idle is the worst case condition for alternator cooling. The Orion will limit the current from the alternator to something around 30 amps so this arrangement is probably better than charging a battery directly from the alternator. I say this because a battery at low SOC could draw much more from the alternator.

The alternator without a battery connected to it is not going to work well as you discovered. The alternator needs a battery to stabilize the voltage.

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fordens avatar image fordens commented ·

"The alternator without a battery connected to it is not going to work well as you discovered. The alternator needs a battery to stabilize the voltage."

Not sure about what you mean, can you please explain, do I need even a small battery in parallel with Orion for the voltage stabilising? Means I cannot connect the alternator directly to Orion?

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Kevin Windrem avatar image Kevin Windrem fordens commented ·
That is correct
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Justin Cook avatar image
Justin Cook answered ·

An Orion is a battery-to-battery charger, so should never be connected straight to the alternator - that'll be the first problem.

Secondarily, I'll note that the Orion 12/12-30 will output up to 30A to the target battery, but to do so it can pull anywhere between 35 and 45A from the source battery, depending on circuit efficiency and operating conditions.

Alternators vary pretty dramatically by manufacturer in terms of their continuous output ratings vs their maximum output ratings, but a general rule of thumb that works well to avoid alternator damage is to take your alternator's output rating, divide it in half, subtract chassis loads (ie ignition, lighting, electronics, etc) and whatever you have left is what you have to play with for a DC-DC charger. So, for a 60A alternator, you'd have 30A continuous available, minus chassis loads (could be anywhere between 5-30A or more depending on your onboard stuff) and you'd have anywhere from maybe 20A to play with to, well, 0A.

Tl;dr: Yes, when the necessary calculations are not performed and the unit(s) are not correctly installed, damage to alternators can certainly occur.

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fordens avatar image fordens commented ·

"An Orion is a battery-to-battery charger, so should never be connected straight to the alternator - that'll be the first problem."

Can you please explain, the Orion is advertised as "For use in dual battery systems in vehicles or on boats where the alternator and the start battery are used to charge the service battery." Not mention about being a battery-to-battery charger.

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Justin Cook avatar image Justin Cook ♦♦ fordens commented ·
The alternator charges the start/source battery, the Orion pulls current from the start battery and pushes it to the auxiliary battery. In all cases, the "input" side of the Orion must be connected to a battery.
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fordens avatar image fordens commented ·
Justin, thanks, I did replace one of the alternators (feeding the starting battery) with a brand new 70ah A127 Lucas type and done some trials.

Indeed, if running at idle 800rpm the alternator doesn't kicks in and no current produced at all. In this case the Orion pulls whatever it can from the starting battery and I ended up with 11.8v still going down. Also, it heats a lot which I suppose caused the problems to the previous alternator.

When revving up to 1000rpm, the alternator starts producing about 25-28 amps, at 1100 rpm I have a steady 39-40 amps and about 13.2v so charging both the starting battery and the lithium bank via Lynx BMS. Good cooling, I read 160C temperature on it.

So there for me is a little difference between isolated and non-isolated Orion in my case, my engine must run at 1100-1200rpm when charging so no draw from starting battery happens at all. Only when slowing down when passing the moored boats the RPM may drop to 1000 but still keep voltage about 12.5v.

For the second alternator, I guess I have an option to stick there a small size battery, say 60Ah just to keep the alternator running correctly, or connect in parallel the second Orion with the first one, taking few more amps from the first alternator. For the second alternator then the plan is to get the Wakespeed WS500 and charge direct into BMS.

Thanks for all your replies, very helpful

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kevgermany avatar image kevgermany ♦♦ fordens commented ·
Did you look at changing pulley sizes to increase alternator revs as I suggested?

Given your alternator sizes, paralleling the Orions as you intend is likely to give problems.


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fordens avatar image fordens kevgermany ♦♦ commented ·
Yes I did look extensively into this question and it looks like I will have a massive issue if changing the crank pulley size or belt type.


If I change the crank pulley size I will have side torque issues, also, just removing the pulley apparently will free a damper ad cause a oil leak unless done properly in a workshop which cannot do a the moment. I either unscrew the pulley or leave it alone.

Second issue, changing type of pulley from V to ribs I will have to rework all the alignments and probably make some bespoke brackets.

All getting complicated, I would better of use this engine as it until it dies and get a new one with a proper setup

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Kevin Windrem avatar image Kevin Windrem fordens commented ·
You could change the pulley on the alternator to a smaller one. Much less impact on the entire system
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kevgermany avatar image
kevgermany answered ·

Twin alternator setups on canal boats are usually configured as one for the starter battery and a second, bigger one for the house bank. This prevents starter battery depletion by the house loads.

Paralleling like this isn't a good idea.

Assuming you have a dead alternator, suggest replace it with a much larger one (say 150A or more), and attach a small AGM and two or more Orions in parallel to that source. Follow @Justin Cook - Bay Marine Supply USA advice on sizing.

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kevgermany avatar image kevgermany ♦♦ commented ·

Afterthought... Some makers, might be beta marine, put alternator pulleys on that increase the alternator revs due to the long periods spent on idle and at low revs. Might be worth investigating this.

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fordens avatar image fordens commented ·

"Paralleling like this isn't a good idea."

Nothing was set up in parallel, one alternator was directly hooked up into an Orion, second alternator was wired up in parallel with starter battery and connected to Orion.

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