How are NAMBA's battery spec rules interpreted for cell count?

[Coug90]

I noticed the table showing official specs for different classes in NAMBA. P-Limited for motor and cell configurations. The cells show 3-4 with max voltage of 16.92 volts and max mah of 10000. Does this mean you're allowed to have 3-4 lipo cells in your boat in regards to cell count or does it mean you are allowed 3-4 cells in regards to 3S-4S of any configuration based on nominal voltage rating? Can a person run only 4S1P or two 2S1P or could they run 4S2P, which is actually an 8 cell configuration? Please share your understanding of how the rule is interpreted, thanks. I ask because it's my understanding that company's are not required to disclose cell configurations on the consumer packaging but are required to list nominal voltage and safety warnings. Unless you open them up and count the cells, you no way of knowing how many lipo cells make up the pack if it simply says 4S or just states the nominal voltage on the packaging. We are in the midst of considering battery rule proposals in our club and want to take this into account. Cell count may a mute point if it's not regulated on packaging. It seems only fair to open up the rule to allow any configuration as long as it meets the nominal voltage limitations. In order to keep things more affordable and try to limit the "arms race" effect, we're considering setting a smaller limit on mah capacity. 10000 mah seems a bit excessive. Your thoughts?

[Steven Vaccaro]

We've run (2) 4s 4000mah packs in parallel. It was much easier on the packs. But you bring up a good point.

[lohring]

The mah is a little harder to police than cell count. At big events the total voltage is always checked, usually through the balance connector. The label is usually the only check on mah. Look at namba.com/content/library/propwash/2024/April/#page/7 and namba.com/content/library/propwash/2024/October/#page/10 for more than you wanted to know about batteries.A testing procedure is described for batteries, but it's time consuming and should only be used in a serious suspected case.

Lohring Miller

[Peter A]

Some years back I drove a change to our rules in Nz to 6000mah for P and Q classes, mainly to try and keep reasonable budgets and affordable classes, (curtail the cheque book racers a bit also) and batteries were easy to get. A couple of years ago I proposed changing back to 10,000 mah limits which went through. One of the main reasons for the change back was how much harder it is to get good batteries here. No one wants, or has options to ship them to New Zealand. Now people can utilise whatever configuration they want as long as they exceed 10,000 mah.
It's about boats on the water and keeping people interested.

I was getting batteries from Wayne Shutte in Aussie, but he sadly passed last year. We have a local drone shop that stocks SMC batts which are probably the best we can get for now, but limited stocks often.

[chrisbrown77]

It's a voltage and capacity limit, not number of cells. 4S = the voltage limit. For 1/7 and 1/8 it's 8S. One pack or two - both will get you there.
They did away with the KV spec for p-limited - just can size now. Some local clubs do limit KV.
So evo motors are king. With a wire drive you have a mid-70's p-limited.

[lohring]

NAMBA and the various Pacific Northwest scale groups all have a KV spec. That plus the propeller diameter is what limits current. Current times voltage equals power.

Power Specifications
i) Motors shall not exceed the manufacturer’s kV rating of 860 kV
(950kV breakout threshold).
ii) Motors may not have a motor case exceeding the following
dimensions, including any bearing protrusions:
(a) Length: 105 mm (4.134 in.)
iii) Diameter: 42 mm (1.654 in.Motors without permanently marked
factory kV rating will undergo technical inspection to verify rule
compliance.
iv) Twin motors are not allowed.

[chrisbrown77]

Mitch - on capacity limits - namba is considering raising them due to running time for longer heats. Our club runs 5 lap heats and as long as they don't extend the loop too much, you can usually make it through on 7K mAh or so lipo pack for p-limited. If you get penalty lap and/or do a milling lap or two, that 10K may not be enough. Definitely not enough for nationals type competition.

Secondly, most 5K mAh packs are now 5200, so you have to either go down in total for a pair, which tend to work better than a single, so at current market availability you're over the 10K mAh capacity limit. And you are right in that battery makers can pretty much slap whatever they want on the label for C-rating and capacity - some are accurate and some are not.

For the bigger FE classes I do think there's a higher limit, but 8S is just so much more efficient it's not necessary. In reality, it was a mistake limiting to 4S in the first place since 6S is also just so much more efficient. I digress...

Anyway, if you're looking for a level field, consider other limits, max prop size, can size, KV, etc. Personally I don't care for KV limits either, run what works in your boat. If a guy overloads his boat with pack capacity he's going to be too heavy. So it's all a trade off.