Series/Parallel switching to charge in parallel, Part 2 - Simplified
UPDATE: April 30, 2008 Please click here
This is a continuation of:
"Bank Charging" by charging in parallel, w/one charger.
The goal is to get the benefits of bank charging without the expense and bulk of having to use multiple chargers. This thread covers a much simpler way to do it than that covered previously. This is best done for lower-powered systems, because a large block of high-powered Anderson powerpoles would be difficult to connect/disconnect, and high-amperage fuses are more expensive. Plus, if you screw something up, your going to get a BIG spark, and possibly a fire or being burnt! Having smaller wire and smaller fuses to the charge connector is nice safety feature for a high-power system.
I had a discussion over PM with e-doggies, and he mentioned using a "jumper harness" in the charging connectors in the drawing (check above link) to wire the batteries in series. This eliminates the need for the high-power connectors in blue, provided the charge connector, and charging wiring can handle the high power when the EV is in operation.
I've seen mr_exon do this, and mf70 also mentions using a "series-parallel plug". Just to give credit where it's due; this is not my idea! I just wanted to help spread it, and incorporate some of my thoughts to help you all.
Here's the basic idea:
I'd upsize the wire from stock slightly. Here's what I would recommend:
Small scooter/ebike: 10 AWG, Anderson PP45 connectors
Large scooter: 8-6 AWG, Anderson PP75 connectors
I recommend using Anderson Powerpole connectors, because they are modular and each contact is completely isolated from the others with plastic. They can only connect when oriented 180 degrees opposite, so once the mating connector is constructed, it will only go in the right way. This makes it easy to use jumpers (see below) to reconfigure the pack on the fly as the connectors are universal. I got mine here: http://www.powerwerx.com .
It would be very helpful to label which connectors are to which batteries. And also label which connectors are to the main positive and negative of the pack. This is why I set them up so the positive and negative for each battery are adjacent to each other. This'll make it easy to measure each battery's voltage, or load test each battery.
Here are some advantages:
● All of those listed here(check bottom of post).
● Safer because just one connector can re-wire the batteries. Because the "ride" connector must be removed to insert the "charge" connector, than there's no risk of wiring the batteries in parallel and series at the same time, if the connectors are setup properly. This does not mean you can eliminate having one fuse per battery! All of them are necessary to protect each circuit from shorts!
● Easy and quick to rewire the batteries for charging or riding.
● Possible to load test each battery from the connector. This'll make it easy to find a bad battery. NOTE: be sure not to exceed the current that the fuses are rated for when doing this.
○ A convenient way to do a load test if your controller has no low-voltage cutout, is to remove the ride connector, and jumper one battery's positive and negative to the main positive and negative respectively. This will power the scooter from just that one battery.
○ If the charger is a smart type that can diagnose battery problems, than you can connect it to each individually battery and watch how the battery accepts charge, and for any codes.
● If you decide to increase the system voltage, than you won't need to buy another charger, just some more anderson powerpoles which can be added to the existing connectors.
● Easy to connect a range-extender battery pack.
● Easy to "break in" the batteries, as you can just connect the charge connector to power a 12v-120v inverter powering a lightbulb and clock. This way there won't be any risk of over-discharging the batteries because inverters usually have a low-voltage cutout, and when it does cutout you'll see by reading the clock.
● Easy to run with the batteries in parallel for a low-speed mode by just inserting the charging connector (or 1/2 voltage (see below)). This will also reduce the potential to damage the batteries when riding on low charge. This will probably not work if your controller has a low-voltage cutout. Beware: you can still damage the batteries by going below 10v/battery.
○ This can be done with a controller that has a low-voltage cutout, if you have a controller bypass contactor.
● Can bypass a battery on the road to get home if one battery dies. You can keep some "jumpers" to do this. The jumper would consist of a wire with two powerpoles on each end. You'll need N-1 jumpers as batteries, so that you can wire the other ones in the circuit as well. This will prevent the need to break up the run connector which wouldn't be so easy if it is nicely assembled with short and direct interconnects.
● In an "oh ****" situation when a controller fails closed (directly connecting the batteries to the motor) the connector can function as a disconnect if it is accessible when riding. Note: Only recommended for small scooters, as the larger powerpoles may be difficult to remove in a panic.
● Can charge from a range of DC-DC converters that have a 13.8v to 15v output. This makes it possible to charge more efficiently from batteries which store solar/wind energy, or from a larger ev which has a DC-DC converter.
● A 48v pack can have a connector wired to have two 2-battery strings in parallel for half voltage. A 72v system could have three 2-battery strings in parallel for 1/3 voltage, or two 3-battery strings in parallel for 1/2 voltage.
● If you've got an ebike with a bursh PM DC motor than you can insert the charge connector (or a 1/2 voltage connector (see last bullet), and install a contactor to bypass the controller to get regen! Best done if you've got a really steep hill to go down, and you've already used some charge from the batteries.
● If it turns out wiring the batteries in parallel to charge doesn't work for any reason, than you can easily traditionally bank charge with N number of chargers for N batteries.
● You can keep a small low-voltage emergency pack of NiMH, NiCads, or LiFePo4 to charge your scooter in an "oh ****, I'm out of charge" situation.
That's all I can think of for now; my brain needs a recharge.
PS: If your wondering why I spent so much time explaining this setup, it's because I clearly have no life. I also want to use this for myself and it helps me understand it.
PPS: I have no doubt parallel/series switching beats bank charging and that's why I'm doing it for my motorcycle and scooter.
Here's the discussion with e-doggies:
I really like the "parallel charging" scenario. So much so that I am incorporating it into the new wiring on my rebuilt Currie Scooter. Each batt terminal will have a single 10awg wire to a "cluster" of Power Poles. All four "-" to one 2X2 "receptacle" (I am running 4 12V 12Ah B&B's), and all four "+" to another 2X2 in close proximity. Probably try to mount them in a box or panel. Each battery charger cable would then need to branch into 4 10awg conductors that are crimped and locked into a 2X2 "plug".
Do you have any good (or otherwise) suggestions on how to fasten 4 10awg wires to the end of one battery charger cable?
When I unplug the charger cables from the scooter, I can replace them with a "jumper harness" to get the pack in series for discharging. I could even easily reconfigure from a 48V 12Ah pack, to a 24V 24Ah pack, just by changing the positions of the jumpers.
I got it all worked out in my head except the part about splitting the battery cable into 4 conductors. I just can't "see" a neat way to do that. Appreciate any ideas.
Thanks again for all you do.
P.S. Do you have a good source for PowerPoles? Looks like they are widely used in the Radio industry. A fair selection at westmountainradio.com
That's a really good idea. I don't know why I didn't think of that. If you care to post what you are going to do in the original thread, than I can add a link to the topic post to your reply. Here's the thread.
I'm trying to figure out how to combine the wires too. I think I'll probably use a terminal standoff with a large 6 AWG or other lug, and stick all the smaller wires in the lug, then crimp and solder it. I have some terminal standoffs that are similar to these here. But they are a little different, I can send a pic of them when, but I don't have them with me right now.
Than the stock charger clamps can be used, or the charger wires can be crimped to lugs and bolted to the terminal standoffs if the charger will remain on board. This also makes the terminals accessible in case you need to charge with jumper cables from a car, or to power an inverter or something.
Another maybe better option I just thought of is to combine the wires into an anderson connector. It would have to be a larger connector to have a large enough wire size lug, like maybe the 75 amp size which can handle 6 AWG. Than, a mating connector can be put on the charger, and a connector can also be made with just open wires so that jumper cables can attach. This also cuts down the bulk some, as you could remove the charging connector without having to unbolt it from a terminal standoff. This sounds like a better solution for your application.
A third option is if you can find a 6 AWG or larger splice crimp connector maybe at a hardware store. Than connect 6 wires into one side, and than you can use a 10 AWG wire out the other, and solder it after crimping, than cover with heat-shrink. The wire out can be put to a smaller Anderson connector to reduce size and cost.
Anyway, I have a suggestion. It's a good idea to have fuses on each battery terminal in your case. Every circuit should have a fuse to prevent fires from shorts (think of house burning down!). I would use some blade automotive fuses in the little in-line holders they have. The closer to the battery terminals, the better. In order to cover every possible circuit for a short, every battery terminal needs a fuse, or 8 fuses for your application. I know the automotive fuses are only rated at 32v, so I don't know what the dangers could be to using them in a higher voltage circuit. I tested some 15 amp ATO fuses at 72v, and the fuses broke the circuit without exploding, so I'm going to use these on my motorcycle. I should of got a video. On one test, I blew away almost half of the fuse terminal in a fireball.
I ordered some Anderson connectors from http://www.powerwerx.com . They also have some blade fuses and holders.
I just realized that a 6 AWG lug or anderson connector will probably not be large enough for 4 10AWG wires. Here's a wire size chart http://www.powerstream.com/Wire_Size.htm You may need to use 14 AWG out from the Andersons in the charging connector, as that'd make it easier to combine them.
I had planned to have one 40A blade fuse inline at the positive terminal of the 48V pack. The controller is 35A so I thought a 40 fuse would be right.
I did notice that you had a fuse on every terminal in your drawing on the thread about parallel charging. I assumed you had them there in case you forgot to unplug one of the interconnects. Since I will be completely removing the "series jumper harness" before charging is possible, there should be no chance of a short, right?
I have no problem adding fuses and connectors, just trying to understand why it's necessary (or desireable). Is it a bigger concern because of the higher voltage? 48V?
Have you ever tried the round glass inline fuses? Neater looking installation. I found some last night (forgot what site) that were had gold-plated compression ends. Now that's Elegant!
I guess my question might be this. What's the risk if I decide to have only one inline fuse in the whole 48V pack? What would be some logical reasons for it to blow? Shorted motor/controller/wiring? I'm uber sensitive to fires, since I had an arsonist pay me a visit in Virginia. Should be only one of those allowed per paying customer. Very Stressful Time. So, I don't want my batteries to send me back there. What situation might cause a fire if there were insufficient fuses?
I'm just trying to play out any shorting scenarios. This setup is kind of unique, in that there is risk of shorting a single battery, or a section of the pack. And since the wires to each battery are drawn out (instead of a direct connection to adjacent battereis like in normal series string) it's a real good idea to fuse each battery now. A fuse is a way to try and protect from a short because you can't always be sure the wire insulation will hold up, especially on an EV with a lot of vibration and harsh environments.
Think of it this way. When building a larger car or truck conversion, one might have two main battery packs. One in the front and one in the rear. But, it's recommended to have a fuse for each battery pack. This is because if the interconnecting wire contacts the other main power out of one of the packs, than kaboom! The pack that's not fused sends thousands of amps through the wire, and it'll start a fire pretty fast.
Even these small batteries can provide a hell of a lot of shorting current. I shorted two 12v 12ahr batteries with a small wrench, and it blew away part of the wrench, and instantly the wrench was hot enough to burn me. Luckily I haven't shorted my motorcycle batteries yet, but I have a lot of work coming up on it, so we'll see how that goes. Like I said, I shorted 72v of batteries in series (and some of these were just small 2.3ahr 12v batteries) to a 15 amp fuse to see what would happen. There was a fireball about an inch in diameter, and the terminal was half way gone, even before the fuse filament melted.
Anyway, enough said, it's your own risk, but I highly recommend a fuse on each positive or negative battery terminal as close to the battery as possible. You can cut the fuses down to half as many as I have in the diagram I realized, because you won't have any direct interconnecting wire, so shorting current has to travel through a positive and a negative 10 AWG wire to complete the circuit (which depends on the short), so fusing one will do. But if there were separate interconnecting wires, than this wouldn't be true like I have in my diagram.
So that's 4 fuses, one for either + or - of each battery.
PS: If your wondering why I spent so much time explaining this setup, it's because I clearly have no life.
Welcome to the club...
Okay, this is brilliant. Totally brilliant.
One question with this is.. the maximum rated powerpole housing is for 180 amps: http://www.powerwerx.com/product.asp?ProdID=35823&CtgID=1020
My motorcycle has bursts of 300 amps draw, and I'm sure yours does as well. Clearly there are two solutions I suppose.. use multiple powerpoles in parallel to have higher capacity... or just trust that the short burst of 300 amps will be okay even though it's beyond the rating of the connector. FWIW you won't be connecting and disconnecting the circuit while it's running power.
I think a similar method could be used with their 350 amp housing, the SB 350. But it won't be as flexible.
I hope the PP180s can handle it. I'm planning to send upwards of 600 amps through them. We'll see.
Okay, this is brilliant. Totally brilliant.
Or not. Maybe Todd's idea of using diodes will work, I'll see tomorrow.
I realized I could setup one PP180 Powerpole and test it today.
I tested it at 600 amps for 10 seconds. To do this, I had to wire two batteries in series. The load tester jaws were smoking, and the load-tester 4 AWG wire got warm to hot.
I felt the contact surface of the PP180 right after the test. It was barley warm. The 2 AWG wire I had in the circuit was warm to the touch.
I guess it's important to note that these are rated for power transmission. And, the specs Anderson gives for pulse current are very conservative. The pulse current graph says I can pulse 600 amps for 3-4 sec through the PP180. I can probably pulse 600 amps for over 30 seconds with marginal heating.
2 AWG wire is only rated for 94 amps power transmission, and 4 AWG is 60 amps.
I finished the more complicated setup of doing this on my bike. Here's the setup:
"Bank Charging" by charging in parallel, w/one charger
Comments here: Re: Re-amped the beast
In general, I would not do this for a high powered system. Anything requiring larger than PP45s (and 10 AWG wire) I would shy away from due to the time required for setup, hassle dealing with the connectors, and expense of the components. This makes it a fair option for small scooters, ebikes, and pocket bikes. Also, it can be done with multi-pole and multi-throw switches which might be an easier to manage system when done.
For example, a 24v system appears to only need one DPDT (double pole double throw) switch. It looks like it would take N-2 poles as the number of battery terminals, and half of those double throw.
I have (4) 12V 20Ah AGM's wired with individual leads from each terminal to a block of PowerPoles. On the charger-side of that connection, all negatives go to one stand-off and all the positives to another. Then I can just clamp the stock 12V charger to the stand-offs.
My question is this:
Once the entire pack has been parallel charged with the 12V charger, which is the best wiring configuration in which to let it rest:
1. Disconnect the charger clamps from the stand-offs and let the pack rest in parallel as 12V 80Ah?
2. Disconnect the charger "plug" from the scooter, and allow each 12V 20Ah battery to rest on it's own?
3. Disconnect the "charger" plug and reconnect the "ride" plug and leave the pack in series as 48V 20Ah?
4. It really doesn't matter at all?
Harlow, funny that you mention it, I'm doing the same thing to charge using terminal standoffs:
I usually just leave mine in parallel until I'm ready to ride. I don't think it matters much though, as charging them in parallel should have charged all of the batteries to 100% SOC, and that is the goal of doing this. It shouldn't hurt to leave them in parallel until you are ready to ride.
The main risk is if one battery has a shorted cell, then it will pull the other batteries down in voltage. It is probably best to not leave them paralleled if the scooter will sit for an extended period of time.
It's not too "funny". I got the idea from you in one of your e-Mails. You have a very neat set-up on your bike. I didn't want to find a place for on-board stand-offs, so mine stay with the charger in the garage. My little scooters never leave the neighborhood. If I traveled, I would want the stand-offs to stay with the bike so I could charge from anyone's standard 12V charger.
Thanks for the advice. The easiest for me will be to completely disconnect the charger plug from the PowerPoles and let the batteries sit as individual 12V 20Ah, until it's time to ride, and then plug in the series jumper. I can see the plugging in and out alot can be tedious. Switches would be a lot easier, but not as failsafe as changing connectors.