B2B chargers: isolated or non-isolated?

[nicknorman]

15 minutes ago, Francis Herne said:

Sitting on the uxter plate, they were at 2° when the canal was frozen a couple of inches thick. I'm not especially concerned about discharging, but charging below 5° is discouraged and below 0° prevented by the BMS as that can cause significant damage. I don't have heater pads, and without shore power it's not something I'm keen to burn power on.

It does depend on the charge rate. The issue revolves around pushing more current into the battery than the normal chemical reaction rate can accommodate. One should be able to charge at 1C (current = capacity) at 5 degrees. By zero only 1/2C and below that, maximum current reduces fairly quickly. So it isn’t like something in the battery is turning to ice, it is a reduction in allowable charge rate as the temperature decreases. At the sorts of rates most people charge narrowboat Li, chances are 0 or a bit below is fine.

[redwing]

On 18/02/2023 at 21:54, nicknorman said:

It does depend on the charge rate. The issue revolves around pushing more current into the battery than the normal chemical reaction rate can accommodate. One should be able to charge at 1C (current = capacity) at 5 degrees. By zero only 1/2C and below that, maximum current reduces fairly quickly. So it isn’t like something in the battery is turning to ice, it is a reduction in allowable charge rate as the temperature decreases. At the sorts of rates most people charge narrowboat Li, chances are 0 or a bit below is fine.

How many amps do you get from your alternator when its warmed up Nick ?

[nicknorman]

57 minutes ago, redwing said:

How many amps do you get from your alternator when it’s warmed up Nick ?

I normally leave the alternator controller on 1/2 charge rate (half of maximum field current) which gives 75A at idle and about 95A cruising at 1300rpm. On the fast charge setting, I get 180A or so initially but I’ve set a temperature limit of 90C and at that it settles on about 125A, depending on temperature. 90C is probably over cautious but then again 125A is plenty and if I want more I can turn on the travelpower and get another 60A or so from the Combi. The 125A is at 1300rpm, at lower rpms the max field current is reduced to avoid a heavly load on engine/belt/pulleys at low rpm.

Between 5C and zero C the voltage decreases such that at zero and below, there is very little charge current. The batteries are mounted in the engine bay (modern trad stern) so the engine warms it fairly quickly and I also have some heating mats under the batteries. But even in very cold weather when we’ve been away from the unheated boat, I have rarely seen less than 5C and never less than zero.

 

Edit - just checked my code, below 5C only 1/2 charge rate (1/6th C) and below 1C only the 50% SoC float voltage (ie the voltage that would give no charge current at around 50% SoC). Maybe not quite rigorous enough if the batteries are very low and very cold when the engine is started, I might need to add something to deal with that. But in practice, the SoC is floated at around 50% by the Combi when we are away from the boat so it SHOULDN'T be a problem. But it could be...

Edited February 20, 2023 by nicknorman

[redwing]

On 20/02/2023 at 10:01, nicknorman said:

I normally leave the alternator controller on 1/2 charge rate (half of maximum field current) which gives 75A at idle and about 95A cruising at 1300rpm. On the fast charge setting, I get 180A or so initially but I’ve set a temperature limit of 90C and at that it settles on about 125A, depending on temperature. 90C is probably over cautious but then again 125A is plenty and if I want more I can turn on the travelpower and get another 60A or so from the Combi. The 125A is at 1300rpm, at lower rpms the max field current is reduced to avoid a heavly load on engine/belt/pulleys at low rpm.

Great, thanks Nick.

 

My setup is similar to Tony's, Valences charged by a 60A Sterling cupboard heater, so see about 45A at best at the batteries. This is fine on a long cruise but rubbish when staying put for a few days. I have spoken to Ed re a Mastervolt Alpha Pro which sounds ideal. They have a temp sensor which will look after alt on a long cruise.

 

The alternative is to get another 60A cupboard heater. This would be much cheaper. Sterling have some refurbs in stock and I could fit it myself. One of my concerns is if they will be taking 120A plus out of the alternator continuously on a long cruise.

Another feature of the Alpha Pro is slow? engine mode. I have no idea what this does other than  protect the alt when going slow. Does the Sterling do something similar ?

 

By the by, Sterling have a new range of B2bs, up to 120A. Wonder if they heat the cupboard as well

[nicknorman]

46 minutes ago, redwing said:

Great, thanks Nick.

 

My setup is similar to Tony's, Valences charged by a 60A Sterling cupboard heater, so see about 45A at best at the batteries. This is fine on a long cruise but rubbish when staying put for a few days. I have spoken to Ed re a Mastervolt Alpha Pro which sounds ideal. They have a temp sensor which will look after alt on a long cruise.

 

The alternative is to get another 60A cupboard heater. This would be much cheaper. Sterling have some refurbs in stock and I could fit it myself. One of my concerns is if they will be taking 120A plus out of the alternator continuously on a long cruise.

Another feature of the Alpha Pro is slow? engine mode. I have no idea what this does other than  protect the alt when going slow. Does the Sterling do something similar ?

 

By the by, Sterling have a new range of B2bs, up to 120A. Wonder if they heat the cupboard as well

 

The Alpha Pro III is quite good, only trouble is it doesn't measure current or SoC so you can't terminate charge based on SoC or tail current. If you add in a Mastershunt then it does all that, but at quite a cost. So overall Wakespeed is probably best value. The "slow engine" mode is in fact small engine mode. It reduces the maximum field current at low rpm. The mechanical load from the alternator is roughly proportional to the field current. You set an rpm above which the field curent is unlimited, and below which you get 20% of max field current (or less). So you get a sliding scale of max field current as the rpm increases from idle to some reasonable speed that you specify. Which is very good. Not to protect the alternator but to protect the belt and avoid a heavy load on the engine at idle. Although of course you need the right interface to configure it from a laptop over Masterbus. As to your question about Sterling doing something similar, if you mean a B2B then no, it doesn't know the engine rpm.

Edited February 21, 2023 by nicknorman

[nicknorman]

“You set an rpm above which the field current is unlimited, and below which you get 20% of max field current (or less).” my sentence above not clear (too late to edit), I should have said:

 

You set an rpm above which the field current is unlimited, and set another (lower) rpm below which field current is limited to a maximum of 20%.

 

[IanD]

11 hours ago, nicknorman said:

“You set an rpm above which the field current is unlimited, and below which you get 20% of max field current (or less).” my sentence above not clear (too late to edit), I should have said:

 

You set an rpm above which the field current is unlimited, and set another (lower) rpm below which field current is limited to a maximum of 20%.

 

You can set any steps you want for % field drive vs. rpm, see below:

Edited February 22, 2023 by IanD

[nicknorman]

3 minutes ago, IanD said:

You can set any steps you want for % field drive vs. rpm, see below:

Is that for the Wakespeed? I was talking about the Alpha Pro III

[IanD]

19 minutes ago, nicknorman said:

Is that for the Wakespeed? I was talking about the Alpha Pro III

Yes, I thought that's what you were talking about... 😉

 

(as you say, the Wakespeed is certainly the best solution on the market, but also the most expensive if you already have a smart shunt...)

Edited February 22, 2023 by IanD

[nicknorman]

Having quite liked the Mastershunt when we first got it, I've somewhat gone off it because it doesn't have the ability to manually set the SoC. If you depower and repower it, it goes to 100% and you can't change it. Which is no good if your Li batteries are at 50%! And it has a very long time constant (maybe 5 seconds) on the "instantaneous" measured current. Although my gadgets have access to both that and the BMV712's data, I use the latter in preference because it seems a bit more accurate, and instantaneous. The Mastershunt does have a built in 500A fuse which is useful, but that makes it a rather expensive fuse!