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victron dc -dc charger


jamie preston
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hi, i have a boat with twin alternators, one 75 amp for the starter battery and a separate 175amp for the leisure batteries. the leisure batteries are lithium ion. my alternators voltage is way too high for my lithium batteries, so i want to use the victron dc-dc 12/12 30 charger to regulate the current and voltage to my batteries.  all of the manuals for this product show it being used to charge a starter battery and leisure battery from the same alternator.

can i connect this dc -dc charger straight to my 175 amp alternator with no other batteries connected other than the lithium, what happens if the batteries built in bms shuts off, will this damage the alternator as i have not got the safety of a lead acid still being connected or would the dc-dc charger have a large enough resistance to save my alternator in this event.

thanks

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The idea behind the DC to DC charger is that your alternator charges one battery bank, (in your case, your Lead Acid starter battery), then the DC to DC charger is connected between the starter battery and your lithium bank. 

 

I'm pretty sure this is the video that made me decide to buy one, and I followed what he did when fitting it. It gets very hot in use, so it's a good idea to fit some kind of heat sink behind it.

 

 

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i get what you're saying, but i have a separate alternator purely for charging the leisure bank. wasn't a problem until i changed the lead acid to lithium.

voltage to high, don't want to damage batteries or mess up the alternator

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14 hours ago, jamie preston said:

i get what you're saying, but i have a separate alternator purely for charging the leisure bank. wasn't a problem until i changed the lead acid to lithium.

voltage to high, don't want to damage batteries or mess up the alternator

Connecting an alternator directly to lithium is something that needs a lot of care. I decided against it by using an Orion from the Lead Acid.

 

Someone who knows more than me will hopefully be along to give some help. I dont think the Orion, (DC to DC), is the thing, but I'm no expert.

 

Some use a longer cable to induce some voltage drop..... in fact Heidi uses this technique to fit a 200Ah lithium here:

 

 

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58 minutes ago, Richard10002 said:

Connecting an alternator directly to lithium is something that needs a lot of care. I decided against it by using an Orion from the Lead Acid.

 

Someone who knows more than me will hopefully be along to give some help. I dont think the Orion, (DC to DC), is the thing, but I'm no expert.

 

Some use a longer cable to induce some voltage drop..... in fact Heidi uses this technique to fit a 200Ah lithium here:

 

 

 

Interesting video. She's done exactly the same as me, lithium in parallel with the LA bank with an Overkill BMS. Except I cobbled mine together out of the bare components. 

 

The drawback to all this is there is nothing to protect the Li cells from over charging other than the BMS, which should really only be stepping in to disconnect when the primary charge controller fails to stop charging. I suspect Heidi is just relying on not overcharging (or over discharging) by luck. 

 

Or maybe the LAs actually put upper and lower limits on the Li SoCs. Will have to think about this some more! 

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I cannot see a parallel LA putting limits on the Lithiums.  The terminal voltage at the LA can get up to about 14.6 at the end of charge.  Even higher for some varieties of LA.

 14.6 is higher than you want on the Li and whole the part empty Li will hold it down it will rocket up as soon as you hit the knee.  OK (except the LA will be part charged and sulphating) if you are doing short runs so nothing gets full but 8 hours cruising is probably going to have you in damage territory.

You could of course get an old alternator regulator which only does 13.4 V but that ain't gonna do much charging!  I have not yet tried to find the voltage range to which one can tweak the tractor regulator, but that might be an answer if the range is great enough.  One could then switch in the right resistance in the sensor wire  for an 'idle' voltage at charge termination.

 

Similarly when discharging.  The LA will go to very much lower than 10v if you keep on discharging in parallel.  If you separate it at end of charge it is not there to have any effect.

 

N

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21 hours ago, BEngo said:

I cannot see a parallel LA putting limits on the Lithiums.  The terminal voltage at the LA can get up to about 14.6 at the end of charge.  Even higher for some varieties of LA.

 14.6 is higher than you want on the Li and whole the part empty Li will hold it down it will rocket up as soon as you hit the knee.  OK (except the LA will be part charged and sulphating) if you are doing short runs so nothing gets full but 8 hours cruising is probably going to have you in damage territory.

You could of course get an old alternator regulator which only does 13.4 V but that ain't gonna do much charging!  I have not yet tried to find the voltage range to which one can tweak the tractor regulator, but that might be an answer if the range is great enough.  One could then switch in the right resistance in the sensor wire  for an 'idle' voltage at charge termination.

 

Similarly when discharging.  The LA will go to very much lower than 10v if you keep on discharging in parallel.  If you separate it at end of charge it is not there to have any effect.

 

N

 

 

Did you watch the "Narrowboat Pirate" video Richard cited just above? (I scanned through it at 1.75x speed.) An interesting video even though much of it is about other things (mostly pubs and boating and booze!) 

 

Her dad connected up an off-the-shelf 200ah li 'drop in, direct replacement for LA battery' * in parallel with the LA bank, and they claim it all works fine. They used a long thin piece of wire as a resistor to reduce the charging current being drawn from the alternator as the alternator initially ran at about 95c IIRC, which they deemed too hot. They seem to use just a simple Chinese shut-based ammeter/volt "reader" to monitor SoC but I didn't notice them saying what parameters they expect to remain within.

 

* The Li battery they fitted is, according to the website they bought it from, four bare cells and an Overkill BMS inside a neat and tidy box with two terminals on the outside. The Overkill BMS seems to have a good reputation and comes with user-programmable settings, so I suspect the battery builders have set their own values and are relying on the BMS alone to disconnect if the Li voltage hits either the low or the high knee.

 

I have grave doubts about the wisdom of this as failure of the single BMS pcb will result in four dead Li cells, but my own idea is to use two Overkill BMSs, one set to tighter limits than the other so one carries out the controlling function and the other monitors and steps in if the first one fails. 

 

The Li battery they fitted: https://www.lifebatteries.co.uk/product-page/12v-200ah-bluetooh-bms

 

Looking at that web page again I see it has the Bluetooth interface fitted so she can manually fiddle with the settings. I'm watching the video again to see if they say anything about the settings they are using....

 

Edit to add:

I also see from the battery spec in that link they recommend a charging voltage of 14.6v!

 

"Recommended Charge Voltage 14.6±0.2V

Float Charge Voltage 13.8±0.2V"

 

All very odd....

 

 

 

Edited by MtB
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On 20/01/2022 at 17:53, jamie preston said:

hi, i have a boat with twin alternators, one 75 amp for the starter battery and a separate 175amp for the leisure batteries. the leisure batteries are lithium ion. my alternators voltage is way too high for my lithium batteries, so i want to use the victron dc-dc 12/12 30 charger to regulate the current and voltage to my batteries.  all of the manuals for this product show it being used to charge a starter battery and leisure battery from the same alternator.

can i connect this dc -dc charger straight to my 175 amp alternator with no other batteries connected other than the lithium, what happens if the batteries built in bms shuts off, will this damage the alternator as i have not got the safety of a lead acid still being connected or would the dc-dc charger have a large enough resistance to save my alternator in this event.

thanks

These sort of questions are cropping up a lot recently. Lots of people have fudged solutions involving dc:dc  converters etc.The right way to do it is to fit a smart alternator controller eg the wakespeed or Mastervolt Alpha one. Have a look here:

https://fourcountiesmarineservices.com/lithium-batteries/

Edited by nicknorman
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i have noted all the advice, much appreciated, thankyou. I have decided to  purchase 2 no victron 12/12 30 dc-dc charger which i will install in parallel. will connect a lead acid to the  alternator and wire as per drawing, although this lead acid is purely sacrificial and not used as a starter battery.

also i have opted for the non isolated version as all negatives are connected to the common ground/chasis.

thanks again.

Screenshot (9).png

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Could have had a smart alternator controller which would have done the job much better for less money, but never mind, it’s your money and your decision.

Edited by nicknorman
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Just now, jamie preston said:

could you suggest the make and model the controller please.

Well as I mentioned earlier, the mastervolt alpha pro III or the wakespeed ws500. The former is much cheaper but not quite as flexible. In each case you do need to slightly modify the alternator to expose the connections to the brushes which are then connected to the controller. I don’t know whether this would be within your capabilities, but if not the link I posted is to Ed Shiers’ company, I’m sure he could do this for you, and supply the controller, for not much profit. Please have a look at his website, it is all entirely sensible (and no relation except a satisfied customer!).

 

With your current proposal, you can charge at 60A. I’m guessing that you have something like a Beta 43 with an Iskra 175A alternator. This is what we have. The brush module is held in by 3 screws and is easy to remove to modify, then replace. In fact I got a spare brush module from eBay for under £20 so I modified that one and kept the original as a “fallback”, although so far not needed.

I find that I can charge at up to 120A without overheating the alternator, although normally it’s around 95A in “gentle” mode. That is one advantage - temperature sensing of the alternator to avoid overheating it. Another advantage is the “small engine” mode that reduces alternator output at low engine rpm, to avoid straining the engine, crank bearings, pulleys and belt eg when passing moored boats.

 

Maybe it depends on your normal usage pattern, if you routinely cruise every day for several hours, maybe it doesn’t matter that you are only getting about 1/2 the available output. But if you are going to run the engine just to charge the batteries, it makes sense to make the best of lithium batteries and your alternator’s capabilities.

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you seem to have infinite knowledge on this issue! thankyou for you sharing it. i indeed have an iskra175amp alternator.

i have been running 2 no 110ah valence batteries direct from the alternator since july. with regular cruising, did a run for about 10 days during the summer cruising for approx 8-10 hours per day. no issues noticed at all. i had an occasion seen my voltmeter reading in excess of 15 volts.

didn't like this voltage so thought about trying to regulate the voltage and current to suit the lithium battery charging profile.

i have also acquired 2 more valence batteries so could add an additional 276 ah. total of 496ah. thought that some sort of control would be wise!

i will look into the master volt and wakespeed products.

 

thanks again for sharing your knowledge.

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19 minutes ago, jamie preston said:

you seem to have infinite knowledge on this issue! thankyou for you sharing it. i indeed have an iskra175amp alternator.

i have been running 2 no 110ah valence batteries direct from the alternator since july. with regular cruising, did a run for about 10 days during the summer cruising for approx 8-10 hours per day. no issues noticed at all. i had an occasion seen my voltmeter reading in excess of 15 volts.

didn't like this voltage so thought about trying to regulate the voltage and current to suit the lithium battery charging profile.

i have also acquired 2 more valence batteries so could add an additional 276 ah. total of 496ah. thought that some sort of control would be wise!

i will look into the master volt and wakespeed products.

 

thanks again for sharing your knowledge.


Clearly your setup works … for the time being!  I see 2 issues though:

Overheating the alternator, since the batteries can and will take the full 175A or so until nearly fully charged. The alternator can do this for a while but I think perceived wisdom is that its life will be severely shortened due to chronic overheating.

 

Secondly the charging profile may not be ideal for battery life. You are starting from a position where the batteries can deliver maybe 5000 cycles. Mistreating them will severely reduce the cycle life but even if you lose 75%, you still have 1250 cycles which is a lot to get through! But then again why be wasteful!?
I charge at 14.3v and then, when the current decreases to 5% of capacity, stop charging and go to a float voltage that puts no more current into the batteries. This isn’t fully charging the batteries but if you look at how many more Ah you would get in if you went up to 14.6v, it would be less than 1% of capacity. It seems that taking Li batteries “up the knee” is what may shorten their cycle life and since it doesn’t give any significant gain in state of charge, seems foolish and wasteful.

 

You can fix these problems by taking the existing unmodified charging source (alternator) and massaging (fudging) its output by means of rather expensive and inefficient dc:dc converters. Or you can take control of the alternator at source and make it do what you and your batteries want. The latter seems the better way to me.

Edited by nicknorman
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9 hours ago, nicknorman said:


Clearly your setup works … for the time being!  I see 2 issues though:

Overheating the alternator, since the batteries can and will take the full 175A or so until nearly fully charged. The alternator can do this for a while but I think perceived wisdom is that its life will be severely shortened due to chronic overheating.

 

Secondly the charging profile may not be ideal for battery life. You are starting from a position where the batteries can deliver maybe 5000 cycles. Mistreating them will severely reduce the cycle life but even if you lose 75%, you still have 1250 cycles which is a lot to get through! But then again why be wasteful!?
I charge at 14.3v and then, when the current decreases to 5% of capacity, stop charging and go to a float voltage that puts no more current into the batteries. This isn’t fully charging the batteries but if you look at how many more Ah you would get in if you went up to 14.6v, it would be less than 1% of capacity. It seems that taking Li batteries “up the knee” is what may shorten their cycle life and since it doesn’t give any significant gain in state of charge, seems foolish and wasteful.

 

You can fix these problems by taking the existing unmodified charging source (alternator) and massaging (fudging) its output by means of rather expensive and inefficient dc:dc converters. Or you can take control of the alternator at source and make it do what you and your batteries want. The latter seems the better way to me.

 

and once you get that brush connection you can safely shut it down while running in an instant.

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1 hour ago, Tony Brooks said:

 

and once you get that brush connection you can safely shut it down while running in an instant.

Yes, although no need for anything crude like a switch that breaks the field circuit (which would require a freewheel diode to prevent major arcing) - these alternator controllers use the ignition feed or maybe an oil pressure switched 12v supply to turn them on and off, so you merely have to remove the on/off signal and the alternator controller will shut down gracefully. Of course that signal can easily be routed via the BMS so the latter can shut the alternator off before any cell-disconnecting voltages are approached.

 

Of course the same can be said for a 6 diode alternator, but that doesn’t give the option for adjustable voltage, “small engine” mode etc

Edited by nicknorman
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