NEW Dimension - LTO Battery from GWL Power

[rgleason]

Dwayne can you post a picture of your installation? How you use the packs and protect them? Is there a BMS? What size alt? Whose regulator? Any safety high low cutoffs?

[Dwayne Lister]

Hi Mate,

Unfortunately I can't post any pictures at the moment as I am in Cyprus and the Cat is in the UK

To answer some of the questions.

I use flat pouch cells each rated at 12A/hr, 2.4v nominal. These were available at the right price and happen to be a good fit into the battery storage area.
While experimenting, the current set are arranged as 2x pack of 7P/5S design, giving me a nominal 12v @ 168A/hr (should have been 8P/5C for 180A/hr, but I have kept some cells back after a little charging incident on the bench).
12v would normally be a little less than ideal and just not possible in a LA battery, but it appears fine, and keeps the charge voltage to 14v.
I might go to 8P/6S later when I get some time to rebuild, but it does put the nominal voltage up to 14.4v which gives a charge voltage of 16.8v which is risky to some of the current electronics.

The packs are protected by both low voltage and high voltage isolators, with separate charge and load bus. Load bus has Low volt isolation, charge bus has high volt isolation. (if you low volt the charge bus you can't charge a flat battery )

Charging comes from a shorepower charger - although this is going to change as I am not really happy with this. There is a charge level controller which disconnects the charge once the charge rate reaches a programmable minimum charge rate.
The biggest thing for me with all lithium technologies for house use is that charge should cease completely once they are fully charged - never leave them to 'trickle charge'. They are actually happier to sit at around 80% charge rather than 100% charge if not in use - unlike LA.

I am currently working on the the engine alternator controller, as I have yet to find any controller which really matches the required charge profile for Lithium properly, and almost nothing comes close to LTO.
Essentially I will be controlling both alternators directly using an external field controller, balancing engine RPM, charge voltage, charge current and alternator temperature, with additional monitoring of battery temp, although I never actually expect to have temperature issues there. The controller also keeps track of charge current, voltage, discharge current, and time. It also monitors Solar charge in the same way and will shut down solar charging under the same conditions.

The biggest modulator of charge current under engine charging is actually alternator temp, as the batteries will easily outrun them and they were never designed to run at 100% output for extended periods. The alternators are the original 60A jobbies that came with the boat, only with external regulation. I can happily pump 120A into the battery for around 20mins before things start to get a little too toasty and I back down to around 80 amps or so. Batteries tend to be full (100%) within 1 1/2 hrs or so.
Once the batteries are full, and a steady state is achieved, both alternators are completely shut down, and do not re-energize until the battery discharges at least 20%.

I don't currently use a BMS between cell stacks but do have stack level voltage monitoring. So far the arrays have remained pretty stable and well balanced.

For general house use, these are far far better than the LA that they replaced. They don't suffer the sag under high load or the reduction in voltage during discharge.
The set usually runs between around 25 and 90% charge most of the time.

I was completely unable to find any alternator controller which would shut down the charge completely at 100%, and nothing that would tie in other charge sources as well.

As to the safety of LTO.
I have massively overcharged my first set of these cells as they were originally sold to me as LFP, which have different charge voltages. Net result, some swollen packs which I did not put into the arrays, but they appear to be just fine and still hold charge at close to the original capacity - they didn't even get particularly warm.


Fair winds and calm seas all,

Dwayne

[Rapanui]

The initial post by the OP interested me and I have been researching the characteristics of LTO batteries as they seem to have many advantages for use on boats. From the following literature

https://www.scib.jp/en/download/Tosh...Battery-en.pdf
https://www.scib.jp/en/product/cell.htm
https://www.murata.com/~/media/webre...1cxs231ce.ashx
(One problem in all the literature I have found has looked at the characteristics of LTO in high charge and discharge rates >1C which is way above what most if not all of us can achieve, so you have to resort to extrapolating trends to sub 1C charge/discharge rates)



I have drawn the following:

• They are at least as safe as LiFePo4
• Your can maintain a charge voltage of 2.7V/cell or lower indefinitely
• You can leave them fully charged for long periods without losing capacity, so you do not have to take special measures for long term storage.
• In the Np6S configuration using typical lead charging voltages of 14.4-15.0V (2.4- 2.5V/cell) will achieve at least 90% SOC. So potentially you could mix lead starter batteries with LTO house bank without special charging measures, battery to battery chargers etc
• Using them in the Np6S configuration means that you would need to have charge voltages of over 2.8V/cell (16.8V) to risk damage to the cells.

Against that:

• Energy density in terms of volume and weight are lower than LFP but still much better than lead.
• Limited range of cell formats, cylindrical and pouch the most comon that are available and relatively low capacities <55 Ahr. Somewhat difficult to construct a useable house bank
• Not readily available apart from GWL Power where they are still too expensive.
• Could not find a BMS with any pedigree.

However, given that there is a lot of activity in using these cells for automotive applications because of their astonishing re-charge characteristics and cycle life, it seems to me that there will be a lot of fast development of LTO which should make this technology useable to our community. Energy density and packaging would seem high priorities