"Bank Charging" by charging in parallel, w/one charger
UPDATE: April 30, 2008: Please click here
"Bank charging" is rapidly becoming more popular. The main problems are complexity, bulk, and expense. I'm trying to figure out how to deal with these problems on my motorcycle. I bought 8 1087CBD 10/6/2 amp chargers, and two of them are bad. If it wasn't enough trouble sourcing and paying for the chargers, now I have to deal with warrantying two via the mail. And, when/if I find a way to get 6 of them mounted on my bike, there may be a good probability of any one of them failing within a few months. Using one charger is much more simple, elegant (as PJD mentioned), and less bulky.
Bank charging can be done with one charger by charging the batteries in parallel. The idea is to disconnect the series connections, and connect the batteries in parallel for charging. The series disconnects need to be high-power connectors, such as Anderson connectors. This has been done with good battery balance results. Here's the setup I envision for my 72v bike:
All of the Anderson connectors in blue must be disconnected before connecting either positive or negative charger connector. The fuses are in place to prevent a fire in case this happens. I may actually put the fuses right next to the battery terminals.
This can be done for a 60v scooter by routing the interconnecting wires (in blue in diagram) up to a point that is accessible so they can be disconnected easily before charging. The extra length in wire shouldn't be a problem with 6 or even 8 AWG wire.
This thread is kind of like a sequel to thread: Splitting the output of one charger
Yeah, this is a possibility.
FWIW the EVT 4000 / 168 have the battery pack wired such that each battery goes to it's own (heavy duty) anderson connector and the anderson's are wired to form the battery pack. Connector, Anderson Style SB 50 Series, 6 ga. Red is the kind of connector I mean. The + and - of the battery go to one side of the connector, the other is connected in series to form the pack. On the EVT it's a major job to dig into the vehicle to undo these connections because the batteries have to be removed. But disconnecting these Anderson's would, as you say, disconnect the pack.
The cost here is the inter-battery connections would be longer. And it's always thought to be a good thing to minimize the amount of wire in the pack. You'd be adding wire and connectors, both of which will increase resistance.
The smaller anderson connectors like Contact Housing, Anderson Powerpole, 75 amp, Red are arranged like you say.. but they're only rated for 75A. I suspect your motorcycle is pumping a few more amps than that...?
Intriguing concept. More appealing to me than having a garage full of chargers.
Would it be safe to keep a PakTrakr connected during the parallel charge process? It would show all batts getting the same voltage, yes? Or would it just blow-up?
I know you would be applying the same voltage to each battery, but it does not allow a charger to adapt to the battery and give more/less charge to that battery. Then add in the complexity of having to connect & disconnect those high power cables, it does not seem worth it to me. Wouldn't you have to pull covers off to get to the battery disconnects?
I see a few probelms with this setup, in addition to the inconvenience of having to disconnect those connectors (use normally-closed relays instead?):
1. You will need a very high amperage, 12-volt charger to get a reasonable charging time. If each of those those batteries is 30ah you will need a 50-amp charger to charge them at the customary 0.3c for SLA's.
2. You could end up with the battery damage you are trying to prevent. As each battery reaches a nearly full state of charge, it's resistance rises and charging current drops. The remaining batteries one after another, will be subjected to more charging current, possibly enough to damage them. You could get around this with a charger with a low enough charging current, but then it would take a long time to charge the batteries.
I still think bulk charging, with battery balancers and a good quality charger is fine way to go. It's what I'm using on my two 48 bikes without problems.
But of course, five powercheqs plus a good 72 volt charger sounds pretty expensive.
Another option I haven't seen mentioned on the forum is using both pack and bank charging together. I know sounds crazy at first but stick with me. Most bikes have a pack charger already. Most chargers voltages can be adjusted internally as well. The idea here is to turn down the voltage on the pack charger to the float level for the pack. Then by adding some small 2amp or less soniel chargers (1 for each battery) you have your bank charging.
Charge profile looks like this:
Initiate charge and you have bank charger plus pack charger max amperage as your charging amperage. As the voltage increases the pack charger pushes less and less as it is set to float voltage. Once the pack passes float voltage the only charging amperage is comming from the bank charging chargers. The soniels are small and reliable (fairly easy to find room onboard for them) have a nice charge profile. The soniels do a nice finish charge on each individual battery. Charge times generally work out the same as the pack charger before it was turned down. Wiring and mounting is simple. Charging is plug and play since all the chargers AC feed can come from one source. Nothing to change or reconfigure just plug one cord into the wall and the rest is automatic and onboard for opportunity charging. The pack charger can't overcharge or undercharge any batteries because the soniels take it out of play automatically once the pack voltage rises past where it is set.
One side benefit is partially avoiding the biggest drawback to bank charging. The case where one bank charger has failed to charge and you take off with 4 full batteries and one dead one. Dead one (permanently) becomes the operative word for that battery in this situation very quickly. With pack plus bank charging at least the battery served by the failed bank charger unit is about 80% charged by the pack charger.