The following page is structured to define the auxiliary battery pack for MSXIV. This page builds off of the page created by Micah Black found here Aux Battery - MSXIV
At the moment, the front auxiliary battery pack is designed to be used for the horn and driver fans. It needs to provide at least 12V and needs to be able to withstand supply a current spikes of 3-4Aof up to 10A.
Item | Power Draw | Respective Confluence Page |
|---|---|---|
Horn | 18W120W | Note - the horn is very power - hungry but only needs to be able to be powered for 5 minutes continuously per ASC regs. |
Driver Fans | 14.4W | n/a |
Our previous battery setup of 10S 1P Turnigy 5000mAh NiMH cells (shown below) seemed to work well however it was mentioned that it was draining too quickly as we powered the car using the aux. battery during troubleshooting. If possible, evaluate the possibility of using the a spare SLA 12V (or lithium-ion at non competition settings) battery to power any troubleshooting power needs.
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According to the guidelines, our aux. battery falls under the “Supplemental Batteries” section. According to 8.2.B, other battery technologies will need to be evaluated by Headquarters and details must be submitted before the 4.3.A.2 due date. If approved, use of the SLA will significantly increase the usage time of the aux. battery pack as well as the time between charge.
Maybe a discussion here on SLA discharge rates and the types of SLA batteries would be useful - there are high CCA batteries for engine starters that don't like to be drained, and deep discharge SLA batteries that typically do not support high discharge currents.
Another issue was the battery pack seemed to cut out while attempting to close the relays too early. See the MSXIV aux battery page for details. This could be an indication that the cells in series do not posses equal amounts of charge, but another more likely possibilty is that the ESR of the whole circuit was too high, generating an undervoltage fault while the relays were pulling in with 4A as discussed on that page. LSD (Low Self Discharge) cells hold charge better, many have very little capacity but the Powerex Precharged D supplies 10,000mAh per cell. Link: Unfortunately, due to NiMH’s high discharge rate, this is not controllable without active balancing but it can be managed.
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