LTO Starter Battery

[grinchy]

I've asked the seller some specifics on the charging circuit of the BMS. it is pretty clear they are not the engineering side and a reseller instead. I doubt any support will come from there on the technical side. Nice enough folks though.

 

[grinchy]

Spent a few hours on a Honda Insight forum. Both 5S and 6S LTO in use there for starter batteries. It’s a tiny engine but they were seeing 220A peak on a 1kw starter,
So I think 350a peak for a 1.5kw on the big V8 is possible.
I have a clamp meter and think it’ll read that high, perhaps can test it on the current AGM.

 

[sdnative]

Set the clamp meter to "max" or "inrush" to capture the initial inrush current.

 

[grinchy]

Spent some time refreshing my knowledge on capacitor bank based batteries. These can start the car no problem, but have trouble with even simple loads over time, and of course with steady state discharge. Often run in parallel with a small 10ah or 20ah SLA. Used to start huge engines - 25l diesels, stuff like that. Some banks over 10,000 CCAs.

What seems to be true is that if the LTO 'starter' battery is just for starting (ie, starting only, with the occasional 10 minutes of listening to the radio in ACC, or powering door lights) that there is very little that needs to be done aside from an appropriate fuse. Balancing could be done every year or two, or maybe not at all. Starter will be fine with a couple minutes (worst case) replenishing in some Ah of charge at full tilt.

Where it gets hairy is using the 'starter' battery as a house battery too. Where the capacity at start might be 5Ah. Here the load over time on the alternator could be more than 15 min at full tilt.

Have found some external alternator voltage regulators ($300-$900), mostly marine parts. Am looking for a breadboard high current design to play with so that I can derate the alternator for a long charge pull. Example - rather than run alternator at 150A for 15 min, run it at 75A for 30 min. Or even, if it sees more that 100A of current draw, to only supply 100A instead of try to match.

 

[grinchy]

Here's some discussion on alternator load dumping to manage the voltage / current spike associated. Early in the thread the Sterling ASP was suggested to manage this.

Eliminate Those Automotive Load-Dump Circuit-Protection Headaches

As the automotive industry increasingly relies on electronic systems to improve safety and the overall driving experience, circuit protection becomes more important than ever....

www.electronicdesign.com

In a two battery system, a small SLA is often used for this purpose. The SLA needs to be kept at less than full charge if it is to be useful for this purpose.

 

[sdnative]

I don't think alternator load dumping is an issue if you use a DC-DC charger, or if you don't use a BMS. The issue is if you have the alternator connected directly to the battery and that connection opens under load (from the BMS).

 

[grinchy]

Good point. Here's a mouser cart with a couple likely candidates. The axial versions of these are all non stocked . . . Is the hookup simply adding this in parallel to the alternator +?

https://www.mouser.com/datasheet/2/240/Littelfuse_TVS_Diode_SLD_Datasheet.pdf-269540.pdf

 

[grinchy]

as usual Balmar has an option. Looks like hookup is positive bus bar to ground? And it's unidirectional? It must be so common sense instructions aren't required . . . .

Balmar TSP-12 Spike Ground Protector 12V - e Marine Systems

Balmar TSP-12 build in an additional level of system safety by ensuring an exit corridor to ground should an AC or DC spike invade the vessel’s charging system.

www.emarineinc.com

 

[grinchy]

Most diodes will have a polarity marking. If there's a band around one end, that's the cathode or + end.
Connect + to + and - to -.
It will not conduct anything until the breakdown (protection) voltage is reached.

Hookup instructions for the TVS diode. A fuse can also be added into the + side if desired.

 

[grinchy]

Even better, someone posted a part number from taking apart one. https://www.mouser.com/ProductDetail/Vishay-Semiconductors/15KE18A-E3-51?qs=x89Eq0mR8pDLBu7EthdMSA== . . . only 1.5Kw (which is the starter sizing too), $1.20 + shipping.

 

[slipkid13]

Why? You initial post stated goals but what is the advantage? Seems like a huge headache, expense and hassle when a lead acid will do the trick.

 

[grinchy]

Why? You initial post stated goals but what is the advantage? Seems like a huge headache, expense and hassle when a lead acid will do the trick.

I totally agree a SLA could/should be used. SLA has their own set of drawbacks, which just because we all live with them all the time we just work around or accept. I'm a curious soul and like to learn and to try new things. The cost isn't exorbitant, I think it opens up some interesting design space, and if proved reliable, certainly it won't be worse than an SLA.

I think weight savings (hopefully 30+ lbs) is the biggest why. If I can make it work as a small house battery too, that would be pretty neat as well.

Who know, lots to discover still.

 

[slipkid13]

I totally agree a SLA could/should be used. SLA has their own set of drawbacks, which just because we all live with them all the time we just work around or accept. I'm a curious soul and like to learn and to try new things. The cost isn't exorbitant, I think it opens up some interesting design space, and if proved reliable, certainly it won't be worse than an SLA.

I think weight savings (hopefully 30+ lbs) is the biggest why. If I can make it work as a small house battery too, that would be pretty neat as well.

Who know, lots to discover still.

Fair enough

 

[grinchy]

From the New Car Features for the 2009 LX570

Battery Capacity (5HR) 12 volt 64 Ah
Generator Output 2160 Watts
Starter Output 2.0 kW (the new part number is 1.5kW)

From the Generator section
Type SC6 12v 180A initial output starting speed max 1000 rpm

No discussion about the regulator design or parameters unfortunately.

 

[grinchy]

After much reading and diagramming I think I'm going to start with the most simple design that I think can safely charge from the stock alternator.

So, no DCDC charger. No protection caps. No contactors or other relays. No proxy small Ah SLA ridealongs.

I will be adding a small series resistance to increase the battery resistance seen by the alternator slightly, to provide additional voltage drop under high current loads. This will protect the alternator by reducing charge current demand to non-burn out levels (essentially I'll be mimicking an SLA resistance at high current demand). The cost is that charging is a bit slower and system efficiency goes down somewhat.

I'm also going to use a voltage snubber / TVS diode (18v 1.5kw 60A) because it can't hurt, and I'm not 1000000% sure there won't be some voltage spiking. I am still undecided on the BMS, a snubber would be required if the BMS is used, so it's going in so I don't have to add later.

 

[TeCKis300]

I think that strategy is probably the most pragmatic at the moment given what you're looking to do.

Curious on more a trade space level. What are you looking to achieve over SLA, as you commented on it having drawbacks? I'm hard pressed to see it? I know you said high power inverter earlier. Is that the primary driver for what seems like shoehorning the LTO battery in for? Backing up a bit, I think you might be able to have your cake and eat it too by using a different integration strategy, perhaps fitting the LTO as a aux battery? Combined with a DC-DC charger (even small one), would be all you need to add the functionality you're looking for?

 

[grinchy]

Curious on more a trade space level. What are you looking to achieve over SLA, as you commented on it having drawbacks? I'm hard pressed to see it? I know you said high power inverter earlier. Is that the primary driver for what seems like shoehorning the LTO battery in for? Backing up a bit, I think you might be able to have your cake and eat it too by using a different integration strategy, perhaps fitting the LTO as a aux battery? Combined with a DC-DC charger (even small one), would be all you need to add the functionality you're looking for?

What I don't like about SLA - Weight. Fear of fail to start except under minimal start and key off use.

Aux battery - Doesn't solve the SLA weight issue. Need space for it. Adds some more weight for charging and appropriate cabling, as well as the weight of Aux batt itself. Pro is full house capability and well understood so lots of info available.

Starter Lithium (LTO in my case) - Cut a lot of weight by excluding SLA. Can use for house loads within reason. Great start and key off capabiility. Drawback is managing the charging situation and not a lot of single battery use cases documented to date. Easily scalable as a house solution if proven successfull (just parallel up some more Ah).

 

[TeCKis300]

What I don't like about SLA - Weight. Fear of fail to start except under minimal start and key off use.

Aux battery - Doesn't solve the SLA weight issue. Need space for it. Adds some more weight for charging and appropriate cabling, as well as the weight of Aux batt itself. Pro is full house capability and well understood so lots of info available.

Starter Lithium (LTO in my case) - Cut a lot of weight by excluding SLA. Can use for house loads within reason. Great start and key off capabiility. Drawback is managing the charging situation and not a lot of single battery use cases documented to date. Easily scalable as a house solution if proven successfull (just parallel up some more Ah).

Can't argue with the weight and that does speak to me. I've tried pretty hard in all my mods to add minimal weight. Though I haven't really attacked the problem by removing stock weight.

The failure to start, is that a real or perceived problem? I do a ton of weekend camping and never have a problem with lots of doors open, lights, charging, cellular booster. The reality is that the standard battery has a solid 80Ah reserve. My single upgraded Group 31 has 120Ah of reserve. I don't hesitate to use deep into the reserves on occasion as I know I'll charge it shortly after, and ultimately FLAs are cheap and easy. LED lights do a ton to mitigate draw. I think many perceive the stock battery to have poor capacity, because they may really been dealing with aged or failed batts. Otherwise, a healthy battery has tons of reserve capacity. Then portable solar handles the rest if I'm really using reserves with things like an electric blanket.

Still, I encourage you to give it a try. I know you're more than capable and up to the challenge. Always different ways to skin a cat and just talking through it before you take the jump.

 

[linuxgod]

sub'd.

I'll be interested to see how this works for you. I don't think AH are the only thing that matters for your vehicle though, which is why true deep cycle batteries are bigger and heavier than starting batteries but have less cranking amps. (Cold) Cranking amps are more important. That's actually another reason why LiFePO4 (LFP) are not good for starting batteries (aside from the "don't charge below 0C/32F or you'll immediately kill the battery" problem). I have no background on other chemistries.

Only semi-related - I ordered some 280Ah LiFePO4 cells and a BMS this week to build a battery for my trailer. It will weigh less than my 100Ah lead acid battery (53# vs ~65# by my calculations) but have roughly 4x the usable capacity. It'll get loaded into the pass-through for now (since my SLA battery sits on the tongue and is exposed to rain) and eventually to somewhere inside the trailer where it's better temperature-controlled. Hoping to get everything received and assembled before we head west this summer.

 

[TeCKis300]

sub'd.

I'll be interested to see how this works for you. I don't think AH are the only thing that matters for your vehicle though, which is why true deep cycle batteries are bigger and heavier than starting batteries but have less cranking amps. (Cold) Cranking amps are more important. That's actually another reason why LiFePO4 (LFP) are not good for starting batteries (aside from the "don't charge below 0C/32F or you'll immediately kill the battery" problem). I have no background on other chemistries.

Only semi-related - I ordered some 280Ah LiFePO4 cells and a BMS this week to build a battery for my trailer. It will weigh less than my 100Ah lead acid battery (53# vs ~65# by my calculations) but have roughly 4x the usable capacity. It'll get loaded into the pass-through for now (since my SLA battery sits on the tongue and is exposed to rain) and eventually to somewhere inside the trailer where it's better temperature-controlled. Hoping to get everything received and assembled before we head west this summer.

Which 280Ah batt did you get? I might one day upgrade my camper as it's still on 2x 6V FLA golf cart batts.

If I'm being honest, I've not really needed more battery than this in my camper. It's around 220Ah rated, and 150Ah usable, and a camper has tons more electrical than the even built out overlanding vehicles.