Roypow battery shutting down

[Beerdude77]

So recently I had a S51160P installed in my 2015 Precedent with Navitas 5kW AC motor and 600amp controller. I took the cart on a test run around my neighborhood and was going up a rather long steep hill when the battery shut off suddenly. Navitas was contacted and they recommended reducing the battery current limit. I lowered it to 180amps and it still continued to shutdown on hills. So I had the Roypow removed and am now back to square one. I have been in talks with Extreme Team about their 72v and 48v options. Pretty sure I saw a thread here where someone stated their ET 48v shut down on them when their cart was bogged down in mud or some kind of situation like that. Are these new drop in lithium packs still just a bit too early in their existence and that is what is causing these issues? I am trying to decide if I should just go with another round of lead acid batteries and when I need to replace batteries in 3-5 years (these Navitas systems eat up batteries in my opinion). Perhaps the lithium market with have better systems and maybe even lower prices with more competition. Thoughts?

[WalterM6]

This is my personal opinion. The Roypow and other battery packs are meant for flat area with no big hills. Two hundred amps isn't enough for hilly areas. They told you wrong when they said to decrease the amps to 185A. You should have been increasing it to 300A. Another big problem is that they run the discharge current through the BMS. The BMS should only measure the high and low cutoff voltages, the balance voltages and monitor the charging current and temperatures. PS If you think it was bad now wait until the weather gets cold when the batteries lose a lot of their capacity.

[Pat911]

The off the shelf batteries are okay with standard carts, certainly not okay with modified units. The unit you specify has a continuous discharge of 160A with a 30 second peak of 315A. That is one of the most capable units on the market but still not up to the task of your 600A, 5kW Navitas installation.

A 72v battery is a better solution for your system as the higher voltage will have a resulting lower current draw, all else being equal. You’ll need to get at least a 107Ah battery to equal the performance of the Roypow that didn’t work. If I were you I would be going with a 72v battery that has at least 200A continuous , 400A 30 second peak current to match your Navitas system. Multiply those currents by 1.5 if you go for a 48v battery. In fact, a second Roypow S51160P would have fixed your problem. An expensive solution though.

Alternatively, build your own battery to your own specifications, and as WalterM6 already said, don’t pass discharge current through the BMS. The cells you choose will still have to be able to handle the peak current of your system though.

Cheers
Pat.

[Volt_Ampere]

Most of these drop in batteries are marginal in current delivery - and you are stuck with their performance limitations. If you have a high performance cart, you need better batteries to go with it and a BMS that doesn't limit your discharge current.

[Beerdude77]

Thanks everyone, these responses seem to verify what i thought was the case. I do not think I have the skill level to put something together myself and I would hate to try and then mess something up and either lose a lot of money or worse, cause a fire or something. I guess for now I will plan to put a new set of lead acid batteries in and hope things improve on the market in the future. i sure wish i knew how all this was going to go before I bought the Navitas system. If I could go back in time I would've just bought an alltrax 500amp controller and a cheaper DC motor or Plum Quik upgrade and I would still be getting similar performance....

[WC53]

On most of the current (pun) lithium packs, it seems the battery is limiting the controller vs the other way around. Higher rate cells are more expensive, so it is about a price point for the majority of the users. They run the current through the bms because it is cheaper and to protect the batteries.
A couple of the Expensive custom pack makers will tell you which cells they are using and then you can see detailed specs of continuous amp draw and peak draw durations.
Batteries for Carts should be able to (start) support 200amps continuous as you don’t want to be constantly operating in the upper regions of the battery. My holiday Inn express opinion.
If you look at the cells from a couple of the EV places say a 100ah hour cell will be 200 continuous or 500 for under ten seconds or a 160ah cell which can do 300+ continuous or 480 for 3 minutes. That is a big difference from the cells currently offered. And very different than the needs of cells in a solar config where big storage vs big output is usually needed. Also more $$$$$

The other equation would be, what % of its rated output can a cheap bms actually flow and live? The expensive bms for electric vehicles seem to all use relays and contactors vs cheaper fet’s.
The more I learn…… In a similar light, I have two 12v lithium batteries I bought used for using in place of 35ah lead acid mat. Well, come to find out they would only flow 30 amps continuous and I kept having thermal shutdowns until I adjusted the motor controller to allow a lower peak.
I was told there would not be math!! ;)

[Fairtax4me]

Part of the issue with lithium is its ability (or lack of) to discharge high amp rates.

Similar to AGM or Gel lead acid batteries, if the discharge rate is too high the plates in the battery will burn. With a lead battery that mostly just means the battery goes dead and it won't ever work again.
But with lithium if you spot weld a place between the anode and cathode sheets in the battery the lithium will go into thermal runaway. The LiFePo4 chemistry is less likely to do that than other lithium types, but the trade-off is also that it has less ability to discharge at a high rate. LiPo and Li-ion batteries can discharge at higher rates, but if they get hit, dented, over-temperature, under-temperature, overcharged, or over discharged, they go up like a firework.
So the "safe" lithium chemistry that the majority of these companies are using just doesn't have the ability (yet) to discharge at a high amp rate for extended periods of time, which makes them not always suitable for a modified cart that demands a higher energy output than a stock cart running around on a regular golf course.

Changing settings in the controller to limit current draw from the pack is your best option if you want to retain the lithium setup. Maybe Allied can chime in with some suggestions on the setup you have.
Navitas doesn't sound like they're much help.

[WC53]

The allied type system with 48v modules allows you to increase the number of modules for more amps, at costs…. Over the larger one battery systems.
Have they listed what the amp discharge of the cells are?

[Pat911]

Originally Posted by WC53

They run the current through the bms because it is cheaper and to protect the batteries.

Not exactly true. They run the current through the BMS because it’s simpler and creates a drop in solution. If they didn’t, then the carts wiring would have to be spliced into to disable the controller (key switch) on low voltage conditions and each carts wiring is different. A headache for the manufacturer.

[Beerdude77]

What I can't figure out is why the battery still shut down when I changed the max output to 180amps. Should I have lowered it to say 150? Would that have made it slower than the lead batteries going uphill?