"Bank Charging" by charging in parallel, w/one charger

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andrew
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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:

Parallel_charging_drawing.gif

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

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reikiman
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Re: "Bank Charging" by charging in parallel, w/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...?

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e-doggies
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Re: "Bank Charging" by charging in parallel, w/one charger

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?

astar
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Re: "Bank Charging" by charging in parallel, w/one charger

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?

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PJD
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Re: "Bank Charging" by charging in parallel, w/one charger

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.

Aerowhatt
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Re: "Bank Charging" by charging in parallel, w/one charger

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.

Aerowhatt

andrew
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Re: "Bank Charging" by charging in parallel, w/one charger

reikiman:
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.

True if you need to route the wire so the connectors are more accessible. But, adding a few feet of wire may not be significant in terms of power loss due to resistance. For example, lets say you have a 60v scooter with 6 AWG wire, 5 batteries, meaning 4 interconnects. Each interconnect requires 4 ft extra to route to an accessible location, so 16ft total. At .0003951 ohms/ft, that adds .0063 ohms of resistance or at an average current draw of 60 amps, 22.8 watts. Two Anderson SB120s would add a total of .000544 ohms (.000136 * 4), or about 1.96 watts at 60 amps. With a 1/2 hr ride time until the batteries are dead, and 60 whrs/mile power consumption, this would reduce range by .21 miles.

It is important to do the calculations to determine how much resistance is being added. And make sure to add the resistance that the connectors will add, than multiply the added resistance times the current squared to get the power loss at a given amount of current flow.

reikiman:
I suspect your motorcycle is pumping a few more amps than that...?

Ya it is. I was looking at the PP180, or PP120.

e-doggies:
More appealing to me than having a garage full of chargers.

My thoughts exactly.

astar:
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.

More charge will flow to the batterie(s) that have a lower resistance to the charge current, and vice versa.

astar:
Wouldn't you have to pull covers off to get to the battery disconnects?

Possibly not if you add extra wire to route the disconnects to an accessible location.

PJD:
You will need a very high amperage, 12-volt charger to get a reasonable charging time.

True, but these are pretty cheap due to being mass produced. I can get a 40 amp automotive smart charger for under $100. On the flip side, if I want to charge twice as fast, I can put another charger in parallel without too much expense added. Much cheaper than adding another bulk charger. Note that I would only put chargers in parallel for the CC phase to get a quick boost charge if needed, because this might not work well at end-of charge.

PJD:
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.

But, it would happen in real-time. As one batterie's resistance rises a little, it would draw less current so it would charge slightly slower and the others would come up in charge faster until the DC resistance is equal. At about 80% SOC the current begins to taper off from .3CA (if that is the charge rate) at ~2.45 vpc. It is not an abrupt full current to no current step, but a gradual transition.

Actually, just the opposite may pose a problem. The battery with the lowest resistance to charge current may take more charge current initially and heat up. Imagine charging two batteries in parallel, one at 25% SOC, and the other at 75% SOC. The 25% SOC battery will take most of the current for a good portion of the CC phase until the SOC of the two batteries equalizes. But, your batteries in the pack shouldn't be far out of balance, and I suspect that the difference in current flow will be marginal.

A similar problem I'm thinking of is end-of life. At end of life, one battery might take no charge, and the other batteries may take charge too fast and heat up. Or, one with a shorted cell might steal all of the charge current and heat up very hot.

PJD:
But of course, five powercheqs plus a good 72 volt charger sounds pretty expensive.

For me: 6 PCs: $360
Zivan NG1 Charger: $415

Total: $775 and my batteries are not charging equally with one usually heating up and going over 15v at end-of-charge. On top of that, the PC fuses are blowing occasionally.

Compare to:
Automotive 12v charger 40 amp: ~$100
Connectors, & fuses: $150

Total $250, and I can easily add another one or more chargers for $100 each to double or triple the charge rate to faster than the Zivan for a quick recharge if needed. If the charger fails, I can replace it in a day with a trip to a local hardware/automotive store. If the Zivan fails, I'm SOL unless I keep a slow 72v spare charger. Also, if I've been riding real hard and want to wait for the batteries to cool, I can just select a slow rate of charge so they can cool off while charging, instead of having to wait to put the bike on the charger.

Ya, the connectors may be a pain to disconnect every time, but I like the looks of the advantages for about 1 min to disconnect/reconnect the connectors.

I just thought of a couple of other advantages:

● I can also charge really slowly overnight to slightly improve the life of the batteries by selecting the 10/25 amp rate.

● If I had to have an EV parked outside during the day while partially discharged, I could easily use a 12v automotive solar panel to help reduce sulfation.

● If I run out of charge, I can get a quick charge from anyone with a car/motorcycle and jumper cables.

● Can easily bypass a bad battery on the road, if the connectors are each single contact, and in close proximity to each other.

● I could easily tap off all of my batteries to run a 12v DC to 120v AC inverter in case of power grid failure. Can also easily use the batteries for a 12v power source if need be.

● If I have a PV system, I can connect the PV battery charger straight to my batteries.

● Can keep a small low-voltage emergency charge Nimh/lithium ion pack on board to charge the batteries and get an extra couple miles range in case of dead battery.

● If I had some deep-cycle industrial batteries hooked up for more than 18v, I could use them to get a REAL quick charge in combination with a motor controller. WARNING: Keep the voltage below the gassing voltage (~2.45 vpc), only do this when the batteries are cool, and limit this to a very short duration, unless you have temperature compensated charging. Don't leave them unattended!

● You can use your battery pack in combination with a 12v-120v AC inverter to charge another EV if need be in an emergency.

andrew
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Re: "Bank Charging" by charging in parallel, w/one charger

Aerowhatt wrote:

[Aerowhatt's post]

I think that's a really good idea. That could work well for people that don't want to spend much, or do re-wiring. Batteryspace carries some inexpensive 12v smart chargers like this one. But that's kinda OT; I think it deserves a thread all on its own.

andrew
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Re: "Bank Charging" by charging in parallel, w/one charger

I finished my bike doing this setup, and I don't recommend doing it for a high-powered system. It is great to have the advantages of having it done though! Comments here: Re: Re-amped the beast

Instead, I recommend the simplified forum for a lower powered system like an ebike, scooter, or pocket bike.
Simplified form of doing it here.

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