I’ve found this battery charger for about $20 USD at my local Costco and was wondering what other people thought of it with regards to charging our FRC batteries. My main question for people is, will it work? Is there some thing about this charger in particular you can see that would be “bad” for use with a typical FRC battery?
What stood out to me was the 4A rating and low cost. We’re in need of new battery chargers, and while I’d love to pick up a few of these from andymark, it’s just not in the budget.
While that charger would work, it’s really not worth it. This charger will do so 50% faster, charges 3 batteries instead of one, and already has the battery terminal end on it. Not quite sure what the duty-cycle of the charger you linked is, but I know the one I linked will survive for many years of constant use.
In combination with what Fletcher said, I suspect it’d just be easier to get a 3-gang charger from AndyMark, especially with respect to effort / cost over time.
EDIT: Somehow I missed your last sentence. Yeah, if you terminate SB50s onto the ends, it should work just fine.
You’d have to get an Anderson connector for each one, cut off the alligator clips, and attach the connector on there - not a huge deal, but an increase in cost/effort to consider.
Otherwise, they seem perfectly fine. The 4A limit would mean they charge slower than the 6A the linked AndyMark charger provides - but if you have enough batteries, space, and chargers (at $20 each, you could get 10 chargers for the 3 ports the AndyMark one has!), that wouldn’t be a problem.
Thanks for the supplies so far guys. Yes I know we would need to crimp on our own SB50’s but we have enough rookies and connectors lying about that it shouldn’t be an issue.
This is very true for us. While we have a fair amount of batteries (thinking 10-12), those date as far back as 2012. Only last year were we able to get ourselves a couple new ones. So as far as I am concerned, we only have 3-4 viable batteries at the moment.
If you have only 3-4 viable batteries and get a few more new ones for the 2019 competition season, you might want chargers that are capable of charging at the 6 A limit. Otherwise, the batteries might not get recharged enough between matches at your competitions. This is assuming the 2019 rules are the same as previous years.
Brian,
I would suggest you buy one or two for spares and demos since they are portable and small. It will take a bit longer to charge batteries but that really depends on how far you had discharged them.
Battery life will not be extended by charging at 1 amp. The discharge rate for our use is what shortens battery life. Charging when the battery first comes off the robot also affects charging as the internal temperature of the battery tends to confuse smart chargers.
The multi chargers most teams use, while stating that max current is 6 amps, will likely fall below that current depending on the software for the charger. We purchased an eight port device last year from McMaster when we lost our 6 port device. I really like this charger as it has meters on the front panel to show terminal voltage and charge percentage. It auto senses battery type so it can be used for gel cell and wet cell lead acid batteries without switching modes.
I’d say that looks like a great option and I wish they had those at that price at the Costco’s in my area because I’d pick up a couple for my team.
Despite what the others have said this won’t be appreciably slower to charge the battery than those that have a max 6a charge rate.
It is the state of the battery that determines the charge rate that a smart charger will charge at and it will not charge continuously at its max charge rate.
At this point, I would like to ask the collective about the time to recharge.
My logic goes like this: If we approximate the discharge rate at 100 amps (which is pretty extreme) and the length of time at two minutes, one match uses:
100 amps x (2/60) hours = 3.33 amp hours.
Given the high discharge rate, let’s allow 1.5 times for the actual charge dissipated or 3.33 x 1.5 = ~5 amp-hours.
With a 6 amp charger, we can return most of that in one hour, with the finishing charge taking another hour, at least that’s my logic.
So, since our batteries have a 17 amp-hour capacity, if we can recharge to 80% without having to wait for the finishing charge, we have 17 x 0.80 = 13.6 amp hours available in the battery.
What I’m driving at is asking whether it’s reasonable to think we can get enough charge in a once-used battery for a match with an hour on a 6 amp charger?
Does anyone have a more scientific or experienced answer than my simple minded logic above?
John, your logic is accurate, but there are inefficiencies in the discharge and charge processes that might add (remove?) 20% on both sides of the calculation. Further…
With lead-acid chemistry, the terminal voltage is more strongly affected by state of charge. This means, an 80% battery will have ~13.6 Ah (plenty of energy), but it’ll deliver only about 90% of the voltage compared to a fully-charged battery. Voltage is more important to FRC than overall energy in my opinion.
18 Ah is only when at a 20 hour discharge rate (C20), or 0.9 Amps. At 100 times this, the actual capacity is much, much less. One of my books** says an 18Ah battery will deplete in 3 to 4 minutes at that higher rate. So, you could be losing 50% or more capacity in your 2 minute match at only 90A.
Going from 50% to 80% at 6A is, indeed, about an hour. But going from 80% to 100% takes more than an hour, because the way chargers work: It’s not at 6A as it approaches 100%.
It’s not as simple as it seems.
*Battery Technology Handbook, HA Kiehne, 1989, ISBN 0-8247-8180-5, Fig 4.19, Page 353