Hi. I'm starting to think about replacing the batterys in my emax. Powercheqs are recommended, but at $60 a pop I'm wondering if there is any advantage to them over just having an individual charger for each battery?
The documentation for powercheqs hints that they are doing something when you are discharging the battery, but all anyone on here talks about is what it does during charging. do they kick in when they batterys are not being used, like at a stop light, in order to correct the imbalances that while arise as these batterys discharge? Do they create a delayed response time from the battery?
Even if they are doing something magical while the scooter is at rest they seem like they introduce inefficiency into the system--they are, in bastardized computer science terms, bubble sorting the battery power because they can only balance pairs. I assume this is why they don't recommend them for long chains? What's needed is a merge sort system. The batterys are split into 2 groups. These 2 are balanced against each other. Then each group is split into 2 groups which are balanced, etc. This way if you had an undervoltage battery on one end and an overvoltage battery on the other the power wouldn't have to "bubble" across the good batterys. ...or some other more intelligent way(selection sort) that transfers the power just between the ones that need it. It seems like making these pair balancing power cheqs makes sense from the manufacturer's perspective since you just buy a number of them an configure them however you want, but from the perspective of the owner/designer of an EV do they?
and one more thing...aren't oowercheqs a bandaid for bad batterys? Why not use the hundreds of dollars spent on powercheqs getting good batterys instead?
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Powercheqs work during charge and discharge, and they can extend range significantly as a result (without them your battery pack is dead as soon as one of the cells begins to lose voltage). In addition, they significantly increase the number of charge cycles you can expect to get from your pack, which saves big $ in the long run. It makes no sense to buy a set of new batteries and get only 150 charge cycles out of them when you can get 300+ with powercheqs and then use the powercheqs with a new battery back when you eventually need one.
TO take your Q's in reverse order, no, you shouldn't just spend more for batteries instead of spending money managing their charge. All batteries will develop imbalances between batteries in a pack. No two physical objects are identical, and over the hoped for 500 re-charges, those differences WILL build up. Once the imbalance develops, the results can be catastrophic. The longer the series string, the more critical it is to maintain balance, though even two batteries in series can be killed prematurely this way.
With flooded lead-acid cells, it's a simple matter to equalize charge by gently overcharging -- all that's lost is water. With SLA's and their very limited ability to withstand overcharging, other methods are needed. A very major weakness of the current technology e-scoots is the lack of any battery balancing provision.
I trust the PowerCheq lid'acher relative to _charge_ balancing. I am more skeptical about DIScharge balancing - they can only divert 2A after all, and normal operation requires far more than that, so I don't see how they could compensate for a seriously depleted battery in a string. (BTW, each PowerCheq actually bridges three batteries, so three are used for four batteries.)
There are also other balancing circuits available, from Lee Hart's zener shunt for $.50 to units that match the PowerCheq's cost.
I believe that 12V parallel charging is the best way to go. I've been using four smaller parallel chargers for about a year, and I'm happy with the results. It too has limitations: The individual chargers need to be monitored on every charge cycle; if a charger fails, the pack will not have a usable charge! (I contemplated permanently mounting four units under the fender skirt, and decided not to for that reason.)
An alternate method is to make up a series/parallel circuit and charge all the batteries in the pack as a single 12V unit. This can be relays or a simple plug with a "dummy" that rewires the pack into series for road use. The weakness of this system is the resistance of the plug used, which will be added between every battery in the pack. If relays were used, they could be designed to double as the safety contactors that make the pack safe when not in operation.
Your first point is funny. You are probably correct though. I've seen battery management systems for advanced EV's that monitor all batteries and regulate the amount of charge going to each. With digital VOM's so cheap these days' I've thought about mounting four of them on the handlebars as a poor-man's monitor. Fusing and cabling concerns have stopped me.
While it is true that Powercheqs can only switch 2A at any time, in typical use a rider makes stops along the way and the powercheqs rebalance the batteries continuously whether on the move or at rest. It's fun to see them working away while you make a lunch stop, for example. In this way they can materially increase range by balancing during the discharge cycle in many cases. Of course they also increase range by balancing during the charging cycle as well.
I have been following this post with interest and I feel it it time for me to put in my 2 watts worth. While it is true the PowerCheq can only move 2 amps at a time and you are drawing much more than that from the battery pack I think you are forgetting a simple fact. We are talking about the balance of one battery to another when the PowerCheqs are in use and not supplying the full amp range to the motor. Lets look at a simple example. For this lets use a 24-volt pack. When I hit the throttle and ask for full power say to climb a hill, I may be drawing 20 amps from the pack. The key word is "pack". So let us say there is a 20% difference between batteries. 20% is a very large amount and one of the batteries may need to be replaced. This means battery "A" can put out 11 of those amps and battery "B" puts out 9 of the 20 amps. Now I have an imbalance in the batteries of 20%. At a 20 amp draw the PowerCheq needs to move 1 amp to compensate for the imbalance. So as you can see the PowerCheq is only working at 50% with a 20% imbalance.
I have tried using 3 12-volt charges on a 36-volt pack and while this did help when I replaced the 3 charges with 2 PowerCheqs and a 36-volt charger, that I had, the performance and range of my ride increased from 8 miles to 12 miles. The batteries were not in good shape as I had over discharged them a number of times. When using the 3 battery charges I noted I had to rotate them from one battery to another because they did not all charge equally. The voltage from one battery to another varried by as much as .3-volts. With the PowerCheqs I have not seen a difference in voltage grater than .04-volts at the end of a charge cycle.
W A R N N I N G ! ! ! For those of you using PowerCheqs.
I left my PowerCheqs on my battery pack over the winter and they discharged my 36-volt pack to about 3-volts. If you disconnect the Center wire they will not discharge the batteries during storage. I am happy to say this was the same set of batteries that were about to expire last year and I planned to replace them anyway. I just had to replace them sooner than I thought.
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Quite right. I alluded to this as a limitation of the multiple-charger method.
If/when I revisit the pack wiring in my scoot, I'll probably go with some sort of series-parallel switching. This will let me build safety contactors into the wiring, as well as providing charge (though no discharge) balancing. I can buy a LOT of contactors for the cost of three PowerCheq's!
The convienience factor figures big in this debate.
I assume, that to avoid having to plug in four separate chargers into four separate power and charging receptacles, the four chargers are must be wired together and placed either permanently on-board, or, duct-taped together, all four power cords and charging cords wired together and the plugged in via a 8-prong plug. And, four comparable-capacity 12V chargers will ba a lot heavier and bulkier than a single 48 volt bulk charger.
So, I think a 48 volt charger plus powercheqs is the way to go.
I find the drain from the powercheqs is pretty small. One of my e-maxs went about a month without charging, and pack voltage was down only a couple volts. No battery pack should be put in storage without periodic charging on at least monthly intervals anyway.
On another subject, with the loss of the old forum, a lot of information on making the e-max chargers more reliable was lost. I'll have to prepare a new post on this topic soom.
If you can provide some key words, we may be able to locate the post in our Voltage Forum Archives from the old forum.
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Voltage Forum Archives
1000's of lost images from the old Voltage Forum looking for there owners.
Although I agree with the conclusion reached in the previous post, the example is wrong. Two batteries in series will always provide the same current. It is the voltage across them that can vary.
I think what you are saying is the current load will be shared equally between the 2 batteries which is correct. My example should have been based on voltage and not current, good catch. However the point I was making is the PowerCheq do not see the full current draw of the motor, so a 2 amp max is more than enough to keep the batteries balanced. As I ride I can see my PowreCheqs working. They only flash their LED it never stays on for more than a second.
To clarify the interaction between voltage and current as the voltage output of the battery decreases so does the current. The only thing that stays the same is the load. By load I mean the resistance value. According to Ohms Law amps(I)= volts(V)divided by Ohms(R). Lets look at an example:
As you can see as the volts decrease so does the current or amps, the load stays the same given the throttle position is unchanged and you do not change motors in the middle of your ride. The amps will NOT stay the same.
Moderator Team Captain
Well, in the setup I've got, I have four chargers "siamese-twinned" together. Charger capacity can be 1/4 as great as for a 48V unit, so the size is not too cumbersome.
The output is two cables, each with a three-contact XLR plug. One plug carries chargers "A" and "B", and the second "C" and "D". In this way, there is some alternation between chargers, since I am not rigorous in connecting the "A/B" plug to the same pack batteries, so I am not totally dependent on the cutoff voltage of a single unit.
I don't find having two charge cables a big problem.
As I said before, I don't recommend either having the unit on-board or with a fixed connection to a single battery.