Re: [EVDL] * Discover agms ?
Seth Myers wrote:
> Yesterday I went to the local batery distributor to pick up a
> Trojan T105 or T125 [...] preached to me the virtues of
> the Discover dry cell (agm).
> The chief virtues are the following:
> - no acid (esp since 10 will sitting in the interior
> compartment (we'll have adequate bracing/protection);
> - no hydrogen gasing
> - no acid spray
> - costs about 2x ($325 ish vs $170 ish) as much, but last 2 -
> 2.5x as long
I think you'll find that this is just the usual price differential between floodies and AGMs. Compare the cost of the Discovers to other AGMs of similar size and you'll likely find them to be quite competitive.
> and they seem to have pretty decent performance
> characteristics (124 minutes rc at 75 vs 115 for Trojans, I
> think) so it just seems to be a matter of buying 4-6 yrs.
> worth of batteries up front vs. 2-3. (??)
I've cycled Discover's L16 and T105-size 6V AGMs and they will deliver their rated capacity at 75A.
> I had initially shied away from Discover when I heard
> they were essentially agm, meaning in my mind 200-300 cycles
> before going kaput, but it looks like they are more like
> 1000-1100 cycles at 50% dod (compare vs Trojan's specs of 438
> cycles T105, 492 cycles for T125).
They aren't essentially AGMs, they are exactly AGM.
The Trojan numbers you refer to sound like their "lifetime eneregy unit" (LEU) ratings, not cycles. A 6V flooded battery is typically rated to about 700 cycles @ 80%DOD, and this will increase dramatically at shallower DOD, just as it does for the AGMs.
Without digging up the Discover specs to fins a cycle vs DOD plot, I would expect them to deliver about 300-400 cycles @ 80%DOD, or about 1/2 the cycles of the floodeds. Despite this, they *do* apparently last longer in certain applications than floodies simply because floodies often die well before their rated cycle life due to lack of maintenance and other operationsla abuses. If your floodies die in 12-18months and the Discovers (which require no maintenance) last 24-36months, then one can honestly state that the Discovers last 2x as long.
> I recall Firefly said their lead acid battery
> would end up being something like 5x in price a regualr lead
> acid, so since this is just 2x, these seem like a midway step
> in the firefly direction ...
Not quite. To their credit, the Firefly folks compared their projected prices to those of present AGMs (not floodeds). That is, the Firefly is predicted to cost about 1.5-2x the cost of your Discover (or any other) AGMs, not 1.5-2x the cost of floodies.
There is also nothing revolutionary about the Discovers; they are just a decent quality AGM.
As to actual EV use, I'm not aware of anyone using the 6V modules. Randy at CEV has built a few Neons running packs of the Discover EV31A-As and has been quite pleased with the performance. I've got a 120V set of the Discover EV34A-As in my EV at the moment. It is too early for me to say anything about their cycle life, but my first impression is that the EV34A-As are not as stiff as the elderly Optima YTs they replaced. I would not recommend them to someone as a less costly power battery than Optimas, Orbitals, or Hawker/Odesseys.
However, the EV34A-A is pretty much a drop-in replacement physically for the Optima Group 34 YT. The main difference is that the EV34 is a more conventional flat-plate construction, and has the threaded insert style terminals rather than the automotive SAE posts. The EV34s are 70Ah and 50lb vs the 50 (55Ah?), 43lb YT.
If you are the sort who looks after your batteries, then it would be difficult to recommend any sealed battery over floodies in terms of cost. You will need a decent charger to hope to approach the rated cycle life for any type of battery. If you need to locate batteries in the passenger compartment or someplace where access for routine maintenance will be difficult, then sealed batteries may be appropriate. If you want a stiffer pack, then AGMs may be appropriate.
Note that Discover makes sealed batteries in both gel and AGM types, and the gels tend to have longer rated cycle life than the AGMs. If your application will use discharge rates compatible with the gel ratings, you might be better off using them than the AGMs. This is especially true if you are considering large sealed 6Vers since even a very modest 2-3C rate is 450-700A for a 225Ah-ish module. If you decide to consider gels, you might want to comparison shop against the DEKA/East Penn and Sonnenschein 6V gels since these brands are typically associated with high-quality gels.
Discover's site is at <http://www.discover-energy.com/>.
For subscription options, see