Batteries

For quite a while, I was unsure of what batteries to use. Good EV quality batteries are even more expensive here in the UK than they are in the USA, so it's not an easy choice. Make a bad choice, and you can kiss a lot of hard-earned cash goodbye...

As luck would have it, Paul was having trouble balancing his set of Optima bluetops in his VW conversion. Eventually, he decided to replace his pack, and put new, well-matched yellowtops  in.  We figured I should be able to find  ten good ones from his old pack to use in Mellow Yellow, since I had decided  on a 120volt system.   So for about a year, the truck had ten Bluetops in it. These were always difficult to balance, and a couple of "stinkers" were really limiting Mellow Yellow's range, to about 10 miles max.

By another bizzare twist of fate, the size of the battery box is perfect  for 5 Optimas to fit tightly-packed across, together with a steel frame to hold them down. I really didn't design it  for this arrangement, it just happened !  I really designed it for 3 Optimas across, arranged end-to-end with lots  of space.

  A couple of months ago, Paul told me about WCN Supplies in Southampton, who had a sale on with Dynasty 50Ah UPS batteries available brand new, for an amazing price. I moved pretty fast, and ordered 24 of them!

I modified the battery frame slightly, adding another row to the back, and a couple of "ears" to hold two more batteries in the front row ( makes better use of the space in the battery box ). Now the truck has ten buddy-pairs, so it's a 120 volt 100 Ah battery pack. It's pretty heavy, at almost 1000 lbs, but the suspension seems to be coping just fine

( new tyres will be needed at the back, they're wearing out )

You REALLY don't want the batteries to be able to break loose in a crash, they'll easily kill you if they do get loose - would you want to try to catch a 45 lb battery moving at 60 mph?

 

Here are some pics of the old Optima batteries nestling in the battery box

( this was during the lengthy build process ).

On the left you can see the batteries inside placed in position in the battery box, and on the right is the suspension height even with all this weight on board! 2 1/2 inches of travel left - just like a standard Mini !
loads of Optimas!
 good ride height!


Below are some pics of the battery frame and holddowns. These batteries won't be going anywhere I don't want them to!
The top frame clamps the batteries down onto the plywood, on top of the lower frame.
The top frame is also bolted to the lower frame at the sides, through the wall of the battery box, using M12 high-tensile bolts. ( the battery box walls are removed in the left-hand picture, installed in the right-hand picture ).
The M8 threaded rods are A2 stainless steel, so they won't rust, and the front row also passes through the loadbed's pan into the cabin of the truck, to provide even more attachment points.


top frame
 holddown detail
 all the batteries installed

Update:New Dynasty batteries!

 
 

Battery managment:


I'm got two systems for managing the batteries, with some more planned....

1.

Battery regulators, to prevent individual batteries from overcharging whilst the others come up to charge. These bypass the charging current around batteries that are fully charged.
2.

A scanning system that monitors the voltage of each battery, and will tell the driver about a failing battery. This system tells you about the lowest voltage battery, and will also be able to display the voltages graphically so the driver can compare them at a glance.

Also in the plan is a logging system built using a Microrobotics VM1 computer. This neat little module uses a Hitachi H8 micro, and has its own multitasking object-oriented Basic-like language, called Venon SC. It has battery-backed static RAM, so it can save up lots of data for download later into a PC. In the future, I may also get this to top up any low batteries using a big DC:DC converter, like Lee Hart's battery balancer.

Chargers:

 

On the left are four Lambda power supplies, which I got at a surplus store for approx 1/5th of their original cost from the manufacturer! On the right you can see the regulators in action with the PSUs, look for the glowing orange lamps, they're the regulators' loads. The odd thing is, they all blink together, exactly in time with each other... weird!
In the middle of the load area, in a white box is my prototype battery monitor. The PSUs are in the bottom-left corner.

 

Each supply puts out between 27 and 37 volts, at up to 40 amps, and is fully power-factor corrected. Voltage and current limits are adjusted using multiturn pots, and I've concocted a circuit using a PIC micro and some digital pot chips which allows the micro to have full control over the voltage and current limits.
Together with some opto-isolators, I can use the four of these supplies to make a 120v charger that can stuff a whopping 40 amps at 147 volts into the 120v pack of hungry Optimas, assuming I can find an outlet capable of delivering the 28 amps of 240v power!
The PIC micro will be able to monitor the state of all the regulators, so it'll know when to throttle back the PSUs. I might link it to the battery monitor as well, so it can make intelligent decisions about how to charge the batteries.
That's the theory, anyway, I'm currently in the process of building the mammoth charger. Since the units are quite heavy, I might build them into a big old server case that I've got lying around and have it as an offboard fast charger. There's also the possibility of running some 48V to 15V DC:DCs, to individually charge the batteries using two of these PSUs. I'd then have two spare, just in case!

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