Cheap LiFePO4 BMS?

[Dre]

9 hours ago, nicknorman said:

No I wasn’t thinking about the output end, there is a LiFePO4 setting and I think there is also a custom setting. I was thinking about any control over how much current it takes from the alternator. If you bought a 60A B2B to run from a 75A alternator, you couldn’t decide later that you only want it to take 50A because the alternator was getting too hot.

 

Oh and on your point about the external switch to control the B2B, the Sterling datasheet I picked to look at had an optional connection for the ignition switch, which would control when the B2B operated. Not sure if they all do though.

My Sterling came with jumper connected on terminals 2 and 3. This means that it will sense the higher voltage from the alternator and basically start and stop automatically when engine is on or off (there's also a delay that can be used) . I've removed this and connected a 12v feed instead to terminal 3 which allows me to switch it on and off as I please (I just used a spade connector but I will wire a switch in) . 

With this option not only am I able to start and stop when I want but it also allows me to charge from my lead acid bank directly as the Sterling is capable of Boost (it can charge from a lower voltage). 

I did this last night and it was taking 30A from the lead acid bank! Engine off. I am not sure why and when it decides to reduce the charging current... Possibly dependant on things like its internal heat dissipation and/or how much it can boost from a certain voltage. 

The Sterling also has a half power function which is easily accessible by holding the Setup button for 5-9 seconds. 

Today I'm gonna measure the alternator temps by charging just the lead acid bank and by charging the Lifepo4 at half power but it seems the Sterling has enough options for me to be able to use it one way or another. Infact I think it's an amazing piece of kit! 

 

 

[nicknorman]

2 minutes ago, Dre said:

My Sterling came with jumper connected on terminals 2 and 3. This means that it will sense the higher voltage from the alternator and basically start and stop automatically when engine is on or off (there's also a delay that can be used) . I've removed this and connected a 12v feed instead to terminal 3 which allows me to switch it on and off as I please (I just used a spade connector but I will wire a switch in) . 

With this option not only am I able to start and stop when I want but it also allows me to charge from my lead acid bank directly as the Sterling is capable of Boost (it can charge from a lower voltage). 

I did this last night and it was taking 30A from the lead acid bank! Engine off. I am not sure why and when it decides to reduce the charging current... Possibly dependant on things like its internal heat dissipation and/or how much it can boost from a certain voltage. 

The Sterling also has a half power function which is easily accessible by holding the Setup button for 5-9 seconds. 

Today I'm gonna measure the alternator temps by charging just the lead acid bank and by charging the Lifepo4 at half power but it seems the Sterling has enough options for me to be able to use it one way or another. Infact I think it's an amazing piece of kit! 

 

I didn’t know it had a 1/2 power option, so that’s good.

 

From my perspective one of the main advantages of Li when not cruising, is it’s ability to be charged very quickly. If you can only charge at 30A then it is going to take a very long time to charge up from very low to nearly full, and you will be using a few amps during that time so even longer! Maybe as a longer term strategy you should look to upgrade your alternator to a 90A one (which is about as much as a normal V belt can service) and you would easily double your charge rate which would halve engine running time.

 

We will be able to put 275A peak current into ours (175A from the alternator and 100A from the Combi via the travel power) although I’m sure the 175A will have to be reduced somewhat to keep the temperature down. So a day’s worth of use will be able to be put back in 30 mins or so.

[Dr Bob]

13 hours ago, ivan&alice said:

Would also love to hear from @Dr Bob on this.

 

 

 

Ivan, apologies but a rather long reply to your question “can I use a 30A Sterling BtoB”. I think the quick answer for your particular situation is “maybe not” but likely “yes” for others. I am very tempted for my new set up and it looks like DRE is happy with his. I think Nick's response is the key (30A is too low).

Now, the long story (which answers some previous questions on alternator temp).

First lets go back over what I am using and my experience over the last 12 months. I am using a 150A AtoB on a 2002 Beta 43 with a 90A domestic alternator. On the 'US gel' setting, it nicely backs off current to the Li's at 80% SoC (around 13.9V) so not overcharging. On this setting it also restricts the current to the Li's at around 45A for the first hour then reducing to around 35A after that. I assume this is something to do with alternator temperature restricting the output of the alternator but it could be the AtoB. For summer cruising this is fine. I can forget about the charging and not overcharge or heat the alternator too much. I have measured alternator temps and it gets to around 95°C in the centre of the top of the alternator and around 65°C on the back plate where the diodes are. The typical temp of the top of the engine is around 75°C so that will also drive alternator temp. My engine bay is not well ventilated (I cant see an air intake!). I have tried to 'up' the AtoB setting to the UK gel but it means the current to the Li's goes up to 55A and the alternator temp rises too fast and gets over 100°C pdq. So for me 45A is the max I will do (50% of rated output). So all fine for summer.

However, in the winter it is a different matter. With solar not working well and using 120Ahrs per 24 hours, I need to get as much power back in the Li's. We dont cruise much in the winter so most charging is done while tied up. We therefore run the engine for an hour in the morning and an hour in the evening to warm the water up and charge. Having used 120Ahrs overnight, there is no way I will overcharge the bank so I CAN change the AtoB setting to UK gel and charge at 55A without fear of overcharging as I will never be near full. With the bilge blower on, I can do an hour without the alternator overheating. I can therefore get 110Ahrs back in per day. If I was in the lower setting, I would take 3 hours of engine running as the current is only 35-45A.

This all depends on your adversity to risk and what temp you are going to allow your alternator to get up to. I have decided 95°C on the top is appropriate given that MP and T&B have both blown their 'cheaper' A127 type alternators.....mine is £250 to replace. Also though note that while solar is great in the summer, what happens when we get a spell of 30°C weather? I park under trees so the boat is not too hot. Not very good for solar. With my AtoB, I now have a choice of controlling the Amps I put in.

Now, in your case, I worry that the 30A BtoB is going to be a bit limiting. I am guessing your alternator is a 90A one (you did say you have seen 50A out of it!). If you fit a 30A then that is 30A in. At 85% efficiency you are looking at only 25A out. That maybe fine with solar but in the winter you could be still looking at 4 hours engine running – and in the summer under trees. I think that is too low and you are loosing out on another 20A that the alternator could give you (you are wasting almost half the power available). If you are looking for a 'plug and play' box then you really need to be able to maximise power in the winter but not worry in the summer. I notice DRE is saying you can reduce power by 50% on his BtoB. One solution could then be to fit 2 *30A in parallel and de-rate one of them to get 40A ish or with both at max -50A in winter. Cost though is now going up.

Another alternative is to buy an AtoB like I have but that is £350. The advantage here is that if you have 2 alternators (do you?) then the Amps can be got from both.

I think your need to have a solution for winter is not to rely on the BtoB which will only give you 25A charge. Remember in winter you will not overcharge so maybe just operate without the B2B (but buy one for the summer) ...ie when tied up, bypass it, and just rely on disconnecting the charge on high alternator temp. Best solution is talk to Nick nicely and see if you can Beta test his alternator controller but that means dismantling your alternator.?

Edited May 13, 2020 by Dr Bob

[Dr Bob]

16 hours ago, Dre said:

 

 

At the moment the battery is getting 13.5v and around 50A

Ive just checked the alternator and it's pretty hot. I have an infrared temp gun and the hottest I can measure pointing into the windings is 150 degrees C.

 

I've just turned the engine off as I'm not sure about the alternator... Need to check temps when charging lead acid bank only. Happy so far though 

 

 

Dre, great news. Well done!

See my post replying to Ivan on alternator temps. I feel that if you are going for 150°C then you will be doing an 'MP' or a 'T&B' and cooking your alternator to destruction. I've no basis to say I am right in this but I am going for a max of 100°C on the top of the unit to ensure I dont have to spend another £250 on a replacement alternator. It has worked for the last 12 months!

 

A more important point though. I hope this pic was taken just to show the installation and the battery cover was replaced immediately after the photo! It is essential to have a cover over the Li's in this set up. There are a large number of exposed interconects on the top of the battery and dropping a screwdriver or a spanner when working on the electronics above could cause a fire. The exposed terminals are far worse than on a typical Lead acid installation and are dangerous. I am guessing from the way the wires are running from the terminals, you do not have a cover yet. Please, please fit one. I use a sheet of perspex but in my installation there is nothing above the batteries to fall on them.

 

The BtoB sounds very good. I am considering one for my new boat. I have a few questions on yours which I will post in a mo.

[Dr Bob]

1 hour ago, Dre said:

My Sterling came with jumper connected on terminals 2 and 3. This means that it will sense the higher voltage from the alternator and basically start and stop automatically when engine is on or off (there's also a delay that can be used) . I've removed this and connected a 12v feed instead to terminal 3 which allows me to switch it on and off as I please (I just used a spade connector but I will wire a switch in) . 

With this option not only am I able to start and stop when I want but it also allows me to charge from my lead acid bank directly as the Sterling is capable of Boost (it can charge from a lower voltage). 

I did this last night and it was taking 30A from the lead acid bank! Engine off. I am not sure why and when it decides to reduce the charging current... Possibly dependant on things like its internal heat dissipation and/or how much it can boost from a certain voltage. 

The Sterling also has a half power function which is easily accessible by holding the Setup button for 5-9 seconds. 

Today I'm gonna measure the alternator temps by charging just the lead acid bank and by charging the Lifepo4 at half power but it seems the Sterling has enough options for me to be able to use it one way or another. Infact I think it's an amazing piece of kit! 

 

 

Hey, this is great!?

A guinea pig to test the unit?

The new boat I am getting (3 weeks away) has a 240A alternator and I am thinking of either 2*60A BtoB's or Nick's solution but I dont fancy taking the alternator apart!

The half power function sounds great.

Two questions

- I have read the pdf file from Sterling but cant see the detail of how to customise a charge setting. I think I read that the Bulk voltage to stop charge can be set to within 0.1V but on the diagram and instructions it shows LEDs that are 13.4v, 13.8v and 14.2V and that when two LEDs are lit the voltage is in between. So that says it can be set at 14.0V ....but can you set it at 13.9V or 14.1V?

- It may well be that the unit can be set to one of the defined battery settings and given the way my AtoB works, I would think the US Gel setting might give the right cut off at 80-90% SoC without the faff of trying to set up a custom setting. Will you be able to try a few of the different settings to see if the current out varies and check the termination voltages?

All my experience has been charging at 30-45A and terminating on voltage alone at 14.0V gives me around 90% SoC. At higher charge rates this voltage will be higher. It will be very interesting to see how this unit performs on the different settings.

[jetzi]

1 hour ago, nicknorman said:

If you can only charge at 30A then it is going to take a very long time to charge up from very low to nearly full, and you will be using a few amps during that time so even longer! Maybe as a longer term strategy you should look to upgrade your alternator to a 90A one

 

1 hour ago, Dr Bob said:

Nick's response is the key (30A is too low).

But this isn't really the fault of using the B2B, this is the fault of having a very small alternator. Part of the alternator regulation problem is precisely to regulate down the current to an amount that is not going to cause overheating, so I wouldn't want to put the max into the lithiums anyway. So if anything the fact that the B2B limits the current to 30A is a good thing. If my 70A alternator can only safely supply half that (35A) then that's not because of the B2B, that's because the alternator being too small. Not so?

 

1 hour ago, Dr Bob said:

rather long reply to your question

I deeply appreciate the length! I'll reply to the rest of it shortly.

[Dre]

2 hours ago, nicknorman said:

I didn’t know it had a 1/2 power option, so that’s good.

 

From my perspective one of the main advantages of Li when not cruising, is it’s ability to be charged very quickly. If you can only charge at 30A then it is going to take a very long time to charge up from very low to nearly full, and you will be using a few amps during that time so even longer! Maybe as a longer term strategy you should look to upgrade your alternator to a 90A one (which is about as much as a normal V belt can service) and you would easily double your charge rate which would halve engine running time.

 

We will be able to put 275A peak current into ours (175A from the alternator and 100A from the Combi via the travel power) although I’m sure the 175A will have to be reduced somewhat to keep the temperature down. So a day’s worth of use will be able to be put back in 30 mins or so.

My alternator is 90A already. How fast I charge the batteries with the engine is not too much of a priority to me as I'll have quite a bit of solar to help with that  but remember that like any battery, Lifepo4s life cycles will be reduced if  charged (or discharged) too quickly. 

[Dr Bob]

Just now, ivan&alice said:

 

But this isn't really the fault of using the B2B, this is the fault of having a very small alternator. Part of the alternator regulation problem is precisely to regulate down the current to an amount that is not going to cause overheating, so I wouldn't want to put the max into the lithiums anyway. So if anything the fact that the B2B limits the current to 30A is a good thing. If my 70A alternator can only safely supply half that (35A) then that's not because of the B2B, that's because the alternator being too small. Not so?

 

 

No it isnt the 'fault' of the BtoB but if you can only get 25A out of it, then you are loosing a potentail 10A (to get you to 35A)....so it really isnt big enough for winter use, but then do as I say above and bypass it letting more Amps in and controlling only on alternator temp for the autodisconnect relay.

What is your engine, age etc? It seems quite important to see if the alternator is 90A or 70A (as that may allow you to charge at 45A rather than 25A). Do you have a 2nd engine start alternator? Too many pages to go back over to find where you mentioned it ! ?

[nicknorman]

10 minutes ago, Dre said:

My alternator is 90A already. How fast I charge the batteries with the engine is not too much of a priority to me as I'll have quite a bit of solar to help with that  but remember that like any battery, Lifepo4s life cycles will be reduced if  charged (or discharged) too quickly. 

Solar : great in summer, not much use over the winter.

On the fast charge / cycle life thing, yes I’m sure this is true but then these batteries are designed to be charged at 1C so if as i suspect we end up with around 450Ah, my max of 275A which, allowing for alternator overheating is more like to be around 200A is less than half that. It won’t be a straight line graph of charge current vs cycle life, it will be an accelerating loss of cycles at very high charge rates. In other words I think that the difference in cycle life charging at 0.5 C (225A) vs 0.1C (45A) will be minimal. As you go over 1C the cycle life will start to fall off quickly.

[Dre]

So the alternator temperature is the same when charging the lead acid bank or the lithiums at half power (around 28A)

The hottest i could find with the ir thermometer was 115C. Yesterday it was almost 150C charging at about 52A. 

Also it seems that the alternator is not giving me much more than 30A as the lead acids are discharging at the same time. The old  shunt monitor for the lead acids says by 25A but that monitor is crap and probably out by quite a few amps. Still, my impression is that for my 90A alternator a more realistic B2B would be a 40A max! 

[jetzi]

1 hour ago, Dr Bob said:

I am guessing your alternator is a 90A one (you did say you have seen 50A out of it!). If you fit a 30A then that is 30A in. At 85% efficiency you are looking at only 25A out.

Interesting, I have measured 50A yes but that's with all my DC loads running flat out and a deeply discharged LA. Also as the alternator heats up and the battery charges this drops off a bit to around 45A. It could be 90A - I wish there was an easy way to know - like a plaque on the alternator!

 

I could try to get a bigger B2B, Sterling's next one up is 60A, but Votronic do a 50A and Renogy do a 40A. But then, I'm back to @nicknorman's problem that I'd be guessing what my alternator could handle without heating up too much.

 

1 hour ago, Dr Bob said:

buy an AtoB like I have but that is £350. The advantage here is that if you have 2 alternators (do you?) then the Amps can be got from both.

What's the practical difference between a B to B and an A to B? I gather "B" stands for "Battery" and "A" stands for "Alternator", but in both cases we're talking about using these to charge lithiums from an alternator. So I think I'm missing something important here. Yes I do have a very small secondary alternator that is meant to charge my starter battery - physically it's around a third of the size of by 70A (90A?) alternator.

 

1 hour ago, Dr Bob said:

Remember in winter you will not overcharge so maybe just operate without the B2B (but buy one for the summer) ...ie when tied up, bypass it, and just rely on disconnecting the charge on high alternator temp.

Why would I not overcharge in winter? If I go on a long cruise, surely I might still put too much into my lithiums?

 

1 hour ago, Dr Bob said:

Best solution is talk to Nick nicely and see if you can Beta test his alternator controller but that means dismantling your alternator.?

I'd not be able to ask Nick to build one for me ?- I'm willing to consider making my own, much more basic than Nick's - just cutting the field wire when either a) the SoC of the lithiums is 80% or b) the temperature of the alternator has risen over 95 degrees. And then reinstating the field when both the SoC has dropped to 75% and the temperature is less than 80 degrees. I feel like this would be within scope of my abilities with an Arduino and possible to achieve for around 100 GBP - just a bit less than what the 30A B2B would cost. Although the devil is in the details - Nick mentioned needing a component that I have never heard of before due to the induction surge of cutting the field abruptly, for example. There may be other things like that which I don't know that I don't know - and if I could avoid a lot of the danger by buying an off the shelf unit that actually doesn't cost much more than the DIY components would, then I'd be remiss to not consider it.

[Dr Bob]

3 minutes ago, Dre said:

So the alternator temperature is the same when charging the lead acid bank or the lithiums at half power (around 28A)

The hottest i could find with the ir thermometer was 115C. Yesterday it was almost 150C charging at about 52A. 

Also it seems that the alternator is not giving me much more than 30A as the lead acids are discharging at the same time. The old  shunt monitor for the lead acids says by 25A but that monitor is crap and probably out by quite a few amps. Still, my impression is that for my 90A alternator a more realistic B2B would be a 40A max! 

You seem to have arrived at the same max charge as I use ie 45A dropping to 35A but your temps seem higher.

I would defo try a bilge blower. Peter told me to do that and it reduces temp by at least 10°C by taking cold air from the bottom of the bilge and squirting it on the alternator. I paid £35 for  my blower.

[Dre]

1 minute ago, Dr Bob said:

You seem to have arrived at the same max charge as I use ie 45A dropping to 35A but your temps seem higher.

I would defo try a bilge blower. Peter told me to do that and it reduces temp by at least 10°C by taking cold air from the bottom of the bilge and squirting it on the alternator. I paid £35 for  my blower.

That could very well be the way we measured the temperature. 

I reckon this alternator has been charging at around 40a for almost 15 years so I'm not gonna worry about its normal temp. If I really find that I need to charge faster I'll look into fans and cooling and bodging something up but the moral is.... The alternator is the limiting factor! 

[nicknorman]

On the alternator temperature thing, do we have any “data” as to exactly why people’s alternators have failed when charging Li unimpeded? Regulator? Diodes? Windings? or what?
 

Still not sure what is the maximum sensible temperature and of course different parts of the alternator will be at different temperatures, so where do you measure?

 

Some relevant facts:

 

Iskra website spec quotes ambient temperature range from -40 to +110C. Ambient, as in engine bay temperature, not alternator temperature which will obviously be greater.

 

The alternator regulator chip I’m using has built in thermal control in that it starts to reduce the output voltage if the chip temperature reaches a certain value. That value can be set in the range 125C to 160C. (The chip is available in a die that can be integrated into an on-alternator regulator so this function isn’t relevant to my application, but demonstrates the sorts of temperatures expected at the “cooler end” ie where ambient temperature air is drawn in past by the fan

 

So I wonder if 95C isn’t unduly cautious. But then, who wants to be the guineapig!

[Dre]

Just now, nicknorman said:

On the alternator temperature thing, do we have any “data” as to exactly why people’s alternators have failed when charging Li unimpeded? Regulator? Diodes? Windings? or what?
 

Still not sure what is the maximum sensible temperature and of course different parts of the alternator will be at different temperatures, so where do you measure?

 

Some relevant facts:

 

Iskra website spec quotes ambient temperature range from -40 to +110C. Ambient, as in engine bay temperature, not alternator temperature which will obviously be greater.

 

The alternator regulator chip I’m using has built in thermal control in that it starts to reduce the output voltage if the chip temperature reaches a certain value. That value can be set in the range 125C to 160C. (The chip is available in a die that can be integrated into an on-alternator regulator so this function isn’t relevant to my application, but demonstrates the sorts of temperatures expected at the “cooler end” ie where ambient temperature air is drawn in past by the fan

 

So I wonder if 95C isn’t unduly cautious. But then, who wants to be the guineapig!

That's good to hear! I will gladly make my alternator the guinea pig but I first need to know that if I need to change the alternator, my Beta can take a bigger one without modifications. 

[nicknorman]

29 minutes ago, ivan&alice said:

 

What's the practical difference between a B to B and an A to B? I gather "B" stands for "Battery" and "A" stands for "Alternator", but in both cases we're talking about using these to charge lithiums from an alternator. So I think I'm missing something important here. 

I’m pretty sure that important point you are missing is that an A2B’s purpose is to boost the alternator voltage using a step-up device. It can’t make the output voltage less than the alternator’s own regulator, it can only make it more.

 

Whereas the B2B is step up or step down device, which is why it can go into “float”.
 

Don’t take that as gospel because I’m not 100% sure but it will give you a target to identify if you look at the specs of the two types of device.

 

 

Oh and on the freewheel diode thing, below is an extract from the internal circuitry of the chip im using, which shows it. The 3 connections are the B+A which would be the D+ terminal in your case, the EXC (excite) which is the connection to the rotor brush, and ground. If you replace the MOSFET with your relay, and add the diode as shown, rated at say 10A (well, 5A minimum) then all will be sweet. You will get a graceful shutdown when you open the relay contact. When the relay opens, current will be sucked up from ground through the diode, and that current will fall off over a short time as the magnetic field of the rotor dissipates and the energy is absorbed in its resistance. If it’s a low side switched regulator you will have to move things around a bit but hopefully this gives you an idea of what a freewheel diode is about. It allows the current to continue to circulate around the rotor under its own “momentum”.

 

Edited May 13, 2020 by nicknorman

[Dre]

13 minutes ago, ivan&alice said:

Nick mentioned needing a component that I have never heard of before due to the induction surge of cutting the field abruptly, for example.

If by that you mean a "load dump" (great name ?) Sterling sell an alternator protector though the b2b has protection from a load dump, when say the bms cuts out while the lithiums are being charged 

[Dr Bob]

1 minute ago, ivan&alice said:

Interesting, I have measured 50A yes but that's with all my DC loads running flat out and a deeply discharged LA. Also as the alternator heats up and the battery charges this drops off a bit to around 45A. It could be 90A - I wish there was an easy way to know - like a plaque on the alternator!

 

I could try to get a bigger B2B, Sterling's next one up is 60A, but Votronic do a 50A and Renogy do a 40A. But then, I'm back to @nicknorman's problem that I'd be guessing what my alternator could handle without heating up too much.

 

It looks like the 'hot off the press news' from Dre that he is thinking  50% of alternator rating is a 'safe' way of operating.....exactly as where I am. It is therefore important to know if it is 70A or 90A. What is the engine, age etc. Picture?  Knowing this, you can then choose the right BtoB.

 

4 minutes ago, ivan&alice said:

What's the practical difference between a B to B and an A to B? I gather "B" stands for "Battery" and "A" stands for "Alternator", but in both cases we're talking about using these to charge lithiums from an alternator. So I think I'm missing something important here. Yes I do have a very small secondary alternator that is meant to charge my starter battery - physically it's around a third of the size of by 70A (90A?) alternator.

 

Not a lot, other than the AtoB goes between the alternators and the batteries. One drawback is that they only have 4 or 5 preloaded battery settings but luckily mine works on the lowest voltage one very well.

There is one big benefit though, with the Sterling AtoB, the destructions say you can have 2 alternators input to the AtoB and it will charge the domestic AND engine start. If it works then, you could have your 90A (or 70A) domestic and the 50A engine start giving you 140A rating - so maybe 70A charge. This is however theory and mine doesnt work like that. Yours may however but Sterling wont have a clue. The problem with mine is that if both alternators are fed into the AtoB it only takes power from the small one as the voltages each puts out are different. The 50A produces 14.3V and the 90A only 13.9V. I bought the AtoB when I had LAs and the 13.9V was not high enough to charge them (see Gibbo's comments on crap old automotive alternators - I have one!). So with the difference in voltage, the 50A overheats and the 90A does nothing. I called Sterling and they said the 2 alternators would work if teh voltages were the same - duh!

If your alternators are similar voltage, then you 'may' be able to use the AtoB to get 70A out of the 2 alternators ....but Sterling will not have a clue about this and say the AtoB is not designed for lithiums. In your position, I would try it first, but that is not easy. If you see a 2nd hand one then snap it up!

 

14 minutes ago, ivan&alice said:

Why would I not overcharge in winter? If I go on a long cruise, surely I might still put too much into my lithiums?

 

 

Yes, of course you could over charge here.

What I am saying is that when charging whilst tied up, you will only run the engine for a limited bit of time and hence you cannot overcharge if you batteries were low before you start the engine.

One thing you will learn with Li's is that most of the time, with our pattern of use, your batteries will be less than half full and if you are not motoring too much then they cannot get enough charge in to be full in a day....so you dont have to worry about overcharging.  We seem to be going from say 30% to 70% SoC up and down each day and getting nowhere near the overcharge llimit. This is one of the things that you will get used to with Li's that you dont with LAs. You just forget about how full the tank is.

[Dr Bob]

18 minutes ago, Dre said:

That could very well be the way we measured the temperature. 

I reckon this alternator has been charging at around 40a for almost 15 years so I'm not gonna worry about its normal temp. If I really find that I need to charge faster I'll look into fans and cooling and bodging something up but the moral is.... The alternator is the limiting factor! 

Yep, that's how I started last May when we set off with the new lithiums. By November, I was looking at ways to get 50A in when tied up (a big difference)....hence the blower!

 

19 minutes ago, nicknorman said:

 

So I wonder if 95C isn’t unduly cautious. But then, who wants to be the guineapig!

It probably is too cautious, but MP and T&B can afford to wreck their A127's. My replacement is £250......

[Dre]

2 hours ago, Dr Bob said:

A more important point though. I hope this pic was taken just to show the installation and the battery cover was replaced immediately after the photo! It is essential to have a cover over the Li's in this set up. There are a large number of exposed interconects on the top of the battery and dropping a screwdriver or a spanner when working on the electronics above could cause a fire. The exposed terminals are far worse than on a typical Lead acid installation and are dangerous. I am guessing from the way the wires are running from the terminals, you do not have a cover yet. Please, please fit one. I use a sheet of perspex but in my installation there is nothing above the batteries to fall on them.

Yes good point but I'm fully aware of the danger. I have a rubber mat that I put on them and they are in the wiring cupboard where everything is well fixed. I really wouldn't like to test lifepo4 max short circuit current ??☠️?

11 minutes ago, Dr Bob said:

It looks like the 'hot off the press news' from Dre that he is thinking  50% of alternator rating is a 'safe' way of operating.....exactly as where I am. It is therefore important to know if it is 70A or 90A. What is the engine, age etc. Picture?  Knowing this, you can then choose the right BtoB.

I went to Beta Marine to get the right spares and they gave me the alternator sizes..... And a black and white print of the engine ready to leave the factory ?

[peterboat]

20 minutes ago, nicknorman said:

On the alternator temperature thing, do we have any “data” as to exactly why people’s alternators have failed when charging Li unimpeded? Regulator? Diodes? Windings? or what?
 

Still not sure what is the maximum sensible temperature and of course different parts of the alternator will be at different temperatures, so where do you measure?

 

Some relevant facts:

 

Iskra website spec quotes ambient temperature range from -40 to +110C. Ambient, as in engine bay temperature, not alternator temperature which will obviously be greater.

 

The alternator regulator chip I’m using has built in thermal control in that it starts to reduce the output voltage if the chip temperature reaches a certain value. That value can be set in the range 125C to 160C. (The chip is available in a die that can be integrated into an on-alternator regulator so this function isn’t relevant to my application, but demonstrates the sorts of temperatures expected at the “cooler end” ie where ambient temperature air is drawn in past by the fan

 

So I wonder if 95C isn’t unduly cautious. But then, who wants to be the guineapig!

I can say in car terms they position them for better cooling or add scoops to help, I would think 100c is normal for one. Cars that have poorly placed alternators tend to go through them on a more often basis. MIdway on the engine behind radiators  oil coolers aircon gearbox coolers and power steering coolers is bad very bad!!!

[Dre]

Mind you, they also gave me far too much oil for the engine..... 

[Dr Bob]

14 minutes ago, nicknorman said:

I’m pretty sure that important point you are missing is that an A2B’s purpose is to boost the alternator voltage using a step-up device. It can’t make the output voltage less than the alternator’s own regulator, it can only make it more.

 

Whereas the B2B is step up or step down device, which is why it can go into “float”.
 

Don’t take that as gospel because I’m not 100% sure but it will give you a target to identify if you look at the specs of the two types of device.

Nick, are you sure of this? My reading of the bumph is that the unit pulls the voltage down from the alternator therefore increasing the alternator output current then increases the voltage to deliver to the batteries.

Now, this is where I really dont understand electrickerty. On LA charging you have bulk where voltage rises, then absorption where you have constand voltage and decaying current etc. On the Li's, when half full, you start the engine and the voltage on the Li bank is 13.5V. If you are charging at less than 50A, this voltage rises until it reaches the point where the AtoB cuts back the current (ie it has reached its absorption phase) dramatically, ie mine will be charging at 35A then all of a sudden it is down to 5A when it gets to 14.0V...ie the US gel setting. What is clear though is that the AtoB stops charging at the fast rate once a target voltage is reached which may or may not be the voltage the alternator regulator is set at. In my case on LAs, the alternator would only deliver 13.9V at constant voltage. If however, I had an alternator regulated at 14.4V, I would expect the AtoB to do exactly the same on the Li's ie charge at increasing voltage until it hits the 14.0V limit (on the US gel setting) and then backs off.

What is certain is that the AtoB is not designed to charge Li's but mine does it very well.

[jetzi]

1 hour ago, Dr Bob said:

No it isnt the 'fault' of the BtoB but if you can only get 25A out of it, then you are loosing a potentail 10A (to get you to 35A)....so it really isnt big enough for winter use, but then do as I say above and bypass it letting more Amps in and controlling only on alternator temp for the autodisconnect relay.

What is your engine, age etc? It seems quite important to see if the alternator is 90A or 70A (as that may allow you to charge at 45A rather than 25A). Do you have a 2nd engine start alternator? Too many pages to go back over to find where you mentioned it ! ?

It's a Beta 38 which has a serial number that has worn off, I have "declaration of conformity" documents that specify my engine serial number as WY5039 so I presume it is exactly as old as the boat - 21 years old in November. The engine runs like a dream though - with 5-10 seconds of glow plugs prior, it has started twice a day every day for two years, in the coldest winter and hottest summer, with neither incident nor complaint.

I would love to know what my alternator is. If you have any suggestions of how I could find out, I'm all ears!

The declaration of conformity specifies a 60A, 12V alternator, so I'm guessing that this is the "engine paint blue" secondary alternator (10cm in diameter), rather than the silver larger alternator (15cm in diameter). 60A is not to be sniffed at actually - so if I did go for a combined approach that would add up to 130A total, if my other alternator is 70A - but actually just based on the physical size difference perhaps it is a 90A actually.

Could I use my pair of alternators with a single larger B2B or would this be verboten?

 

Otherwise, I'd have to design my basic alternator controller to monitor the voltage of the batteries as well as the temperature of both alternators and shut them off independently.

I think what I could do in the meantime is see what amperage I can get out of my smaller alternator?

 

Here are some pics of my engine and alternators, perhaps someone can enlighten me - I can also take things apart and send more pics if that would be helfpul.

Edited May 13, 2020 by ivan&alice

[MoominPapa]

21 minutes ago, Dr Bob said:

Yep, that's how I started last May when we set off with the new lithiums. By November, I was looking at ways to get 50A in when tied up (a big difference)....hence the blower!

 

It probably is too cautious, but MP and T&B can afford to wreck their A127's. My replacement is £250......

I'm not anticipating wrecking many A127s. The failure so far is a diode pack on an alternator that's been making most oft he power for full-time liveaboards for five years, and was a cheapy "reconditioned" unit from Ebay when "new".  The experience for a 70A alternator charging a 600Ah LA bank is not significantly different to charging a LiFePO4 bank: in both cases is spends considerable time (hours) turned up to 11.

 

My alternator is at the top of an engine in a well ventilated engine room, which helps. The other thing which helps is that I dismantle it once a year and clean out the substantial dust and fluff accumulations in the air passages. That makes a big difference and I'd recommend it to all as a maintenance practice.

 

MP.