Low priced LiFePO4 Batteries vs High priced

[s/v Jedi]

Originally Posted by Phil_Fr17

Whoops ! You're right s/v Jedi, I carefully reread the documents and the curves that I found odd.
My apologies, I have read too fast and diagonally.


Being in a rush and not fully fluent in a foreign language can lead to this kind of inversion. It has already happened to me several times to misunderstand what I was told in English, the English drive on the left, this is perhaps the explanation of my misunderstanding in a good way... ;-)

No worries, I’ve been haunted by these graphs for so many years that I see them in bad dreams haha.

[AKA-None]

Originally Posted by newhaul

What you are paying for with different brands is quality assurance ( better inspection practices same factory

You can’t inspect your way to quality
Demming

[newhaul]

Originally Posted by AKA-None

You can’t inspect your way to quality
Demming

Not what I said . What I said was. " When you buy a more well known brand while it may be made in the same factory there are more quality assurance inspections done to justify the warranty .

[T1 Terry]

Originally Posted by s/v Jedi

No, that is the other way around: this explains how the characteristics of the contactors change when the ambient temperature changes.

For example: using a lower coil voltage because “it works” may suddenly not work on a very hot day as the graphs show… because when it’s hot, a higher voltage is required.

Solenoids and contactors get hot for two reasons: coil inefficiency and contact resistance. When it gets hot without large currents flowing through the contactor, it is just the coil heating it up and this is what the OP describes. Depending on size of the units, a coil can use between 100mA to several amps just to hold the contact closed. Not all this energy is converted into magnetic field and this part ends up as heat. This heat builds up over time (it’s only a problem for continuous duty applications) until it finds a level where the same amount of heat is radiated out as that is added from the coil and hopefully this heat level isn’t too high. In that case the solenoid or contactor is rated as continuous duty.

Then there are optimizers that reduce coil current to keep the contact closed after switching. I think most continuous duty versions now have that. This reduces heat from the coil as well. Next step are latching versions, which require no coil current to hold the contact closed at all and thus are the most efficient. Of course price goes up as well. The 7718 is a plug-in replacement (https://www.bluesea.com/products/7718/Solenoid_ML_12V) and the mentioned 7713 adds a manual control knob to it.

The problem with latching contactors, they require a pulse to turn on and another pulse to turn off .... not always available if the battery isolation was to avoid cell damage due to over discharging.

The problems we saw with 12v contactors was around 14v being supplied when they really got hot, drop the voltage and the temp dropped. The optimiser coil is just a lower current draw with a lower magnetic field generated, the main coil is designed to slam the contacts closed, optimiser coil is just there to hold it closed, a spring opens the contacts.
If the contacts are getting hot, there is a real problem there some where, probably a loose clamping nut of a poor cable crimp, the actual contacts are not part of the coil section but mounted under it .....
If you drop the voltage back to 10v or so, the heat generated is much less and therefore the wasted power is far less. A variable resistor will give you a method of testing how low you can drop the voltage before the contactor actually trips, about half way between that and the full system voltage will solve the heating problem and save you having to buy another product .....
If you still decide to remove the Gigavacs, drop me a PM and we'll negotiate a price for me to buy them

T1 Terry

[s/v Jedi]

Originally Posted by T1 Terry

The problem with latching contactors, they require a pulse to turn on and another pulse to turn off .... not always available if the battery isolation was to avoid cell damage due to over discharging.

The problems we saw with 12v contactors was around 14v being supplied when they really got hot, drop the voltage and the temp dropped. The optimiser coil is just a lower current draw with a lower magnetic field generated, the main coil is designed to slam the contacts closed, optimiser coil is just there to hold it closed, a spring opens the contacts.
If the contacts are getting hot, there is a real problem there some where, probably a loose clamping nut of a poor cable crimp, the actual contacts are not part of the coil section but mounted under it .....
If you drop the voltage back to 10v or so, the heat generated is much less and therefore the wasted power is far less. A variable resistor will give you a method of testing how low you can drop the voltage before the contactor actually trips, about half way between that and the full system voltage will solve the heating problem and save you having to buy another product .....
If you still decide to remove the Gigavacs, drop me a PM and we'll negotiate a price for me to buy them

T1 Terry

Please check the 7718 and 7713 links I provided before posting incorrect info about them. I wrote that they are -direct replacements-, with the 7713 adding manual control. This means that they are not pulse operated but exactly the same as the Gigavac.

[T1 Terry]

Originally Posted by s/v Jedi

Please check the 7718 and 7713 links I provided before posting incorrect info about them. I wrote that they are -direct replacements, with the 7713 adding manual control. This means that they are not pulse operated but exactly the same as the Gigavac.

Ummmm.... They sure don't look like a direct replacement to me, the Blue Seas unit would never fit in the BMS box to start with ..... Maybe they can be adapted in certain circumstances, but certainly not a direct replacement.

The next problem is I can't see where I referred to the Blue Seas contactor at all in my post, I just mentioned the problems associated with latching contactors and I was referring to the fact a latching Gigavac GX14 was available in the same form factor.
I have no interest in starting a war of words here, I'm just stating what we have done successfully for the past 11+ yrs.
As you can see from the attached images, the contacts are not at the base of the coil, if one was cut apart, there is a plate with two contactor faces and a spring under it that is pushed down via a post
by the electromagnet coil, the matching faces are on the plates the cables bolt to, so there really is no area for heat tranfer from the contacts to the coil ....
https://www.cruisersforum.com/forums/attachment.php
attachmentid=266563&stc=1&d

https://www.cruisersforum.com/forums...068=1667271124

T1 Terry

[s/v Jedi]

Originally Posted by T1 Terry

Ummmm.... They sure don't look like a direct replacement to me, the Blue Seas unit would never fit in the BMS box to start with ..... Maybe they can be adapted in certain circumstances, but certainly not a direct replacement.

The next problem is I can't see where I referred to the Blue Seas contactor at all in my post, I just mentioned the problems associated with latching contactors and I was referring to the fact a latching Gigavac GX14 was available in the same form factor.
I have no interest in starting a war of words here, I'm just stating what we have done successfully for the past 11+ yrs.
As you can see from the attached images, the contacts are not at the base of the coil, if one was cut apart, there is a plate with two contactor faces and a spring under it that is pushed down via a post
by the electromagnet coil, the matching faces are on the plates the cables bolt to, so there really is no area for heat tranfer from the contacts to the coil ....
https://www.cruisersforum.com/forums/attachment.php?
attachmentid=266563&stc=1&d

https://www.cruisersforum.com/forums...068=1667271124

T1 Terry

You quoted me with my post about the Blue Sea product specifically, so yes, I took your reply in that same context. Also, your “pulsed” description is exactly like the 7700 model of that product, while the text you quoted from me was specific and identified the 7718 and 7713 models, not the 7700 that you described.

Yes, they look different

It’s all good, you don’t have to use them… just don’t claim they are not compatible because of requiring pulse control while they are in fact 100% compatible with the same signal that the Gigavac takes, without getting hot, wasting energy etc. Yes it’s more expensive.

[T1 Terry]

Fair enough, I should have either hi-lighted the latching relay part or cut the bit about the Blue Seas contactors from your thread when I quoted it, my bad ...

T1 Terry

[s/v Jedi]

Originally Posted by T1 Terry

Fair enough, I should have either hi-lighted the latching relay part or cut the bit about the Blue Seas contactors from your thread when I quoted it, my bad ...

T1 Terry

No worries, I often fail to put my posts into the right context too with the confusing miscommunication after that

[newhaul]

Originally Posted by s/v Jedi

No worries, I often fail to put my posts into the right context too with the confusing miscommunication after that

And I thought I was the only one .

[CaptainRivet]

Originally Posted by T1 Terry

The big difference in price seems to be split into two different parts, what capacity the battery really is and how well the BMS works.

The first part, check the C rate the capacity is measured with, as an example, C20 for a100Ah battery means you can only use a max of 5 amps if you want to get the 100Ah.
This adds a second catch with the cheaper batteries, is the capacity really 100Ah or does the seller use the 80% available trick meaning you only actually get 80Ah.

A 100Ah lithium battery should be able to provide 50 amps continuous for 2 hrs and each cell still remain above 3v while under load. This is called a C2 load rating, a battery with a C20 load rating will not deliver 50 amps for 2 hrs, many will not deliver 50 amps at any time period, the BMS will not allow that much current draw.

The high end price allows access directly to the cells, you can test, and if needed, replace a single cell, or charge a single cell, or clean the links between the cells. They will last 10yrs or more, that is the experience we have with the Winston cells we use and we have used hundreds if not thousands of these cells over the last 11 yrs building off grid power systems.

We get a lot of the lower price end drop in batteries brought in to see if we can fix them, and even some rather high priced drop in batteries. None have ever delivered the capacity marked on the case tested at 2C, some simply won't deliver 50 amps or accept a charge at 50 amps.

T1 Terry
T1 Lithium

Exactly, good summary Terry.
Cheap LFP make sense
- if you have small current and capacity requirements, eg weight sensitive weekend or race catamaran or a day sailor.
- if you have space and want max capacity because each battery carries less amps and load plus you rarely really use 80% of its capacity. So you can afford more capacity and have backup due to more batteries.

If you have space constrains and therefor small capacity 250AH or less but still want electric galley the 2C Winston cells is the way to go.

In the end You get what you pay for, especially with LFP….you can get lucky with some grade B cells though for a good price.
I preferably would go with 200AH Winston cells then with 500AH cheap drop ins like chin etc….you get much more in the end for same amount of money.