Jump to content

Domestic battery replacement..


Barry Orton

Featured Posts

29 minutes ago, Barry Orton said:

Want to replace 2x SLA with 2x lithium.  Don't want to go hybrid.  Can they just be connected in the same way as the SLA's were or do any extra gizmos need to be added?

 

40A alternator to starter and 100A to domestic.

 

TIA

Yes, if you want to risk your new investment being overcharged, or your 100A alternator being fried.  

You need to stop charging as soon as the Li is full. Not go to float or carry on at 14.6 V.  Stop charging completely.  Switching the charge off without first stopping the alternator producing output may well fry  the alternator.

 

When the battery is not fully charged it will happily absorb all 100 A from your alternator.  All day, until it is full.  The alternator is probably not designed to produce 100 A all day and will get very hot.  If it does not wrap its hand in immediately it will do so after a few days of running too hot.

 

The Li battery may well have a 'battery management system'.  You should not rely on this for routine management of the Li battery. It is really designed as an emergency cut off.

 

There is a huge thread on Li battery management in Boat Building and Maintenance.  It explains how to swerve most  of the problems.  Read it.  You will he much better versed in Li battery management when you have.

 

N

Link to comment
Share on other sites

In fact I would like to go hybrid but, even though I'm convinced of the benefits, I've spoken to 3 different electricians and none of them are prepared to do the "suck it and see" resistance wire method.  Neither do they seem to have much clue about alternative ways to achieve (eg DC to DC Charger?).

The advice I've got at the moment is to have SLA'S and lithium on different charging circuits, that I'd have to switch manually.  That negates the benefit of hybrid for me.

  • Greenie 1
Link to comment
Share on other sites

4 minutes ago, Barry Orton said:

In fact I would like to go hybrid but, even though I'm convinced of the benefits, I've spoken to 3 different electricians and none of them are prepared to do the "suck it and see" resistance wire method.  Neither do they seem to have much clue about alternative ways to achieve (eg DC to DC Charger?).

The advice I've got at the moment is to have SLA'S and lithium on different charging circuits, that I'd have to switch manually.  That negates the benefit of hybrid for me.

You would be well advised to read the thread mentioned above. Then at least you will have some understanding of the reasons the electricians you've spoken to are not going to risk trashing their reputations.

 

Quote

There is a huge thread on Li battery management in Boat Building and Maintenance.  It explains how to swerve most  of the problems.  Read it.  You will he much better versed in Li battery management when you have.

 

Link to comment
Share on other sites

10 minutes ago, Barry Orton said:

In fact I would like to go hybrid but, even though I'm convinced of the benefits, I've spoken to 3 different electricians and none of them are prepared to do the "suck it and see" resistance wire method.  Neither do they seem to have much clue about alternative ways to achieve (eg DC to DC Charger?).

The advice I've got at the moment is to have SLA'S and lithium on different charging circuits, that I'd have to switch manually.  That negates the benefit of hybrid for me.

As usual I will recommend Ed Shiers of Four Counties Marine Services. He knows his stuff when it comes to Lithium. Although he might not tell you what you want to hear - connecting Li batteries direct to a 100A alternator, either with or without LA batteries in parallel, is likely to guarantee a short life for the alternator.

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

 

Link to comment
Share on other sites

Obviously the long length of cable adds resistance and decreases charging current but I wonder how hot 6mm cable gets when passing 100A or so. And is a great length of unfused cable connected to battery + acceptable to BSS? IMO it is relatively dangerous (as these things go) and so should fall outside the rules. I’m not sure it does though! Of course it would be possible to “do it properly” with fuses at both ends and ensuring the cable is located somewhere where hot insulation won’t be an issue, but that certainly wasn’t the case in her video. And in any case, resistance works both ways so when the Li is discharging into her inverter voltage is going to be dropped, cable is going to get hot etc. let’s hope she doesn’t put the electric kettle on, 200A through 6mm cable is definitely going to be interesting.

 

Also it seems like she thinks that insulating something keeps it warm! Only applies to humans and other warm blooded animals!

 

Overall, a really good video on how to do it badly and dangerously. But I’m sure, not untypical of what amateurs without much electrical knowledge or imagination are doing out there.

Edited by nicknorman
  • Greenie 2
  • Unimpressed 1
Link to comment
Share on other sites

19 minutes ago, nicknorman said:

Obviously the long length of cable adds resistance and decreases charging current but I wonder how hot 6mm cable gets when passing 100A or so. And is a great length of unfused cable connected to battery + acceptable to BSS? IMO it is relatively dangerous (as these things go) and so should fall outside the rules. I’m not sure it does though! Of course it would be possible to “do it properly” with fuses at both ends and ensuring the cable is located somewhere where hot insulation won’t be an issue, but that certainly wasn’t the case in her video. And in any case, resistance works both ways so when the Li is discharging into her inverter voltage is going to be dropped, cable is going to get hot etc. let’s hope she doesn’t put the electric kettle on, 200A through 6mm cable is definitely going to be interesting.

 

Also it seems like she thinks that insulating something keeps it warm! Only applies to humans and other warm blooded animals!

 

Overall, a really good video on how to do it badly and dangerously. But I’m sure, not untypical of what amateurs without much electrical knowledge or imagination are doing out there.

Hi I'm interested to , how do you do it safely then ?

  • Greenie 1
Link to comment
Share on other sites

54 minutes ago, luggsy said:

Hi I'm interested to , how do you do it safely then ?

Crudely:

 

Find some cable with insulation which will withstand high temperatures- at least 100 C. Ensure it's current rating is adequate for your planned load.

 

Choose the right length, from current and volt drop calculations.

 

Check the likely cable temperatures from heat dissipation calculations.  Adjust cable selection as needed.

 

Fit a fuse to  the resistance cable at either end.

 

Wind the cable on to a purpose made frame of insulating material, aaàààwith a suitable temperature rating (not some crappy low melt stuff)   in such a manner that you are not creating a big inductance and there is free airflow through the conductors.

 

Mount the frame somewhere it can dissipate the heat generated and provide protection to the electrical connections.

 

Connect up with cables sized for the planned loads and try it.  Measure the cable temperatures at full load.  Ensure these are within the cable's rating.  Measure the volt drop.  Ensure this is what you want, at various currents.

 

Rinse and repeat if the results are not satisfactory.

 

Document it all, so you have proof it was well designed and could not possibly be the cause of the fire that wrecked your boat so the Insurers have to find another reason not to pay out.

 

Wonder why you would install something  which is basically there to waste diesel.à

 

Otherwise  buy a proper Lithium battery alternator controller/A to B device/DC to DC charger.

N

 

  • Greenie 1
Link to comment
Share on other sites

Why does it have to be high temperature and why should it get hot. You use a cable rated suitable for the maximum current its just the length gives the volt drop. Using 2mm cable for a water pump 2 meters away is fine. If you use the same cable for a pump that is 15 meters away it wont get hot but the pump wont run very well due to the volt drop.

I bet Nick's cable between his alternator and his battery isn't fused, but if he gets a short to earth at the alternator it will get very hot with every amp his batteries can muster flowing down it.

  • Greenie 1
  • Love 1
Link to comment
Share on other sites

4 hours ago, ditchcrawler said:

Why does it have to be high temperature and why should it get hot. You use a cable rated suitable for the maximum current its just the length gives the volt drop. Using 2mm cable for a water pump 2 meters away is fine. If you use the same cable for a pump that is 15 meters away it wont get hot but the pump wont run very well due to the volt drop.

I bet Nick's cable between his alternator and his battery isn't fused, but if he gets a short to earth at the alternator it will get very hot with every amp his batteries can muster flowing down it.

Basic physics, if you want to drop voltage you need resistance. If you have resistance and current you have power, which becomes heat. Of course you are right in that if you choose a fairly fat cable that is very long, the same heat is dissipated in the cable but over a much longer length, and therefore the temperature rise is less. But that is not what the person in the video was doing, she was using 6mm cable. And with no fusing.

 

On my own installation I have a 500A fuse built into the Mastershunt, which is adjacent to the battery positive. There is about a couple of feet of 75mm cable that runs over the wooden battery box between battery positive and mastershunt positive. Not really any scope to develop a short. I am well aware of what 600Ah of lithium batteries could do if they are angered, and the thought of 75mm copper cable turning to vapour is not appealing.

Edited by nicknorman
Link to comment
Share on other sites

13 hours ago, nicknorman said:

Basic physics, if you want to drop voltage you need resistance. If you have resistance and current you have power, which becomes heat. Of course you are right in that if you choose a fairly fat cable that is very long, the same heat is dissipated in the cable but over a much longer length, and therefore the temperature rise is less. But that is not what the person in the video was doing, she was using 6mm cable. And with no fusing.

 

On my own installation I have a 500A fuse built into the Mastershunt, which is adjacent to the battery positive. There is about a couple of feet of 75mm cable that runs over the wooden battery box between battery positive and mastershunt positive. Not really any scope to develop a short. I am well aware of what 600Ah of lithium batteries could do if they are angered, and the thought of 75mm copper cable turning to vapour is not appealing.

75mm??

Link to comment
Share on other sites

1 minute ago, Mike Todd said:

But the 75mm was stated just after referring to 6mm cable! Inconsistent use of units is a sure route to misunderstanding and, ultimately, to disaster as I think has been documented in some high profile cases.

But surely my usage of units was consistent? Consistently wrong in both cases!

Link to comment
Share on other sites

Just now, Alan de Enfield said:

 

70mm2  cable

 

Its a hell of a faff (but thats progess, improvements and upgrades for you)

Arrr you going to tell us how you dunnit?

1 minute ago, David Mack said:

Yes.

75mm²

On my phone I hold the '2' key down and get the option of a superscript.

Doesn’t seem to work on iPad.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.