My official Prius Plus mods thread.

<div class='quotetop'>QUOTE(kammssss @ Nov 22 2007, 02:18 AM) [snapback]542836[/snapback]</div>

If you just parallel 2 batteries, how are you going to make sure that one battery doesn't overcharge or undercharge the other? The Prius works to keep the OEM NiMH battery between 39% (lowest) and 79% (highest) state of charge. Even if you parallel an identical, fully charged battery, one battery would end up charging the other.

The OEM NiMH battery is 201v, by the way.

You wouldn't need CAN-View in particular, but you do need something that listens on the CAN bus to determine what the OEM battery's computer is saying the state of charge is. If the state of charge gets low, something needs to parallel the packs. When it gets too high, something needs to unparalllel them to prevent the second pack from overcharging the first.

Chris

 

And I'm still thinking it should be something a little more, uh,
linear than a click-on, click-off relationship... has anyone
scoped the current spikes you must invariably get when the extra
pack's contactors come on?
.
_H*

 

<div class='quotetop'>QUOTE(hobbit @ Nov 22 2007, 09:25 AM) [snapback]542870[/snapback]</div>

I agree that it would be better to have a DCC converter or something like that, but those aren't exactly cheap. Snubbers across the contactors help to some degree, but ultimately, there is no real control of the current when they just click on and off...

Chris

 

<div class='quotetop'>QUOTE(Chris Ewert @ Nov 22 2007, 06:14 AM) [snapback]542868[/snapback]</div>

Hey, thanks Chris...I haven't thought of that. But if the OEM battery has a BMS (battery maintenance system), would it not just reject the 2nd battery's current, since the voltage/amp of the 2nd battery would probably not be in accord with the OEM BMS charging specifications? Also, the 2nd battery will also have a BMS system of its own, so it too will reject the OEM batteries' current. Am I making any electrical sense? Again, I am not an expert in this field. I presume 216v will not do anything detrimental to the Prius' hybrid system, since Cheap! used a 240v configuration. Am I at least correct with this assumption? Thanks everyone and have a Happy Thanksgiving!

 

<div class='quotetop'>QUOTE(kammssss @ Nov 22 2007, 07:09 PM) [snapback]543024[/snapback]</div>

The BMS (which is actually a battery management system) simply monitors the balance of the cells and monitors the health of the battery as well as keep track of the state of charge, etc. The BMS is not capable of "rejecting" a charge. If the battery is subjected to a charge or discharge, the BMS is powerless to actually stop it - it can only make recommendations to the Prius, but it relies on the Prius to correctly limit charge or discharge currents. So if you parallel a second pack (regardless of voltage), the OEM battery can't do anything to prevent it from overcharging or undercharging itself.

The PriusPlus conversion method that Cheap! used uses a 240v battery to charge the 201v NiMH battery. There is a contactor (large relay or switch) between the 2 battery packs. When the OEM battery's BMS indicates that the state of charge is lower than would be desired, the contactor is turned on, and current flows from the 240v battery to the 201v battery. Then, the OEM battery's BMS shows a higher state-of charge and the contactor is shutoff.

240v battery that is paralleled and unparalleled according to the OEM battery's state of charge won't do anything detrimental (other than normal wear) to the OEM battery, so you are correct that 216 shouldn't be detrimental either - as long as it isn't left in parallel all the time, but there probably isn't enough of a difference in voltage to cause current to flow from one battery to another. You have to also keep in mind that as a battery's state of charge decreases, so does its voltage, and the voltage is pulled down easier when the battery is more depleted or cold, so the voltages must be chosen very carefully for that system to work.

But if you are going to just parallel 2 packs and keep them paralleled, the 216v battery will slowly charge the 201v battery and cause the OEM battery to go above its safe range and overcharge the battery. Once the OEM battery goes above 80% state-of-charge, a whole host of bad things can happen (including permanent damage to the OEM battery), so you don't want that. You also don't want it going too low either as that can also cause permanent damage.

I recommend looking at the PriusPlus design:
http://www.priusplus.org/

Chris

 

<div class='quotetop'>QUOTE(Chris Ewert @ Nov 22 2007, 04:31 PM) [snapback]543028[/snapback]</div>

Hey Chris, thanks a lot. You sound like you work for NASA, or at least helped design the Prius. Further, do you think I would really need to worry about one battery charging the other if I commute 45 miles (1 way), driving 65mph? My second battery (216v) should be depleted by then. And when I park, I will have a switch to unparallel the batteries, so the OEM battery will not charge the depleted (216v) battery. Also, do you think these 2 batteries will attempt to charge one another when driving 65mph, or whenever it is in the state of discharging? This is the area where it gets kind of gray for me. Again, thanks a lot Chris. I am just optimistic that there has to be another way to do a conversion without spending all that money and time. I hope I am right...and you will be the first to know if I can get this thing going. Please, any electrical experts out there, tell me I have some hope. Happy Holidays to everyone!

 

<div class='quotetop'>QUOTE(Chris Ewert @ Nov 22 2007, 09:31 AM) [snapback]542871[/snapback]</div>

The step up from the (old reliable) electromechanical contactors is IGBT's switching devices in each leg ( (+) and (-)

 

The prius plus conversion is probably just about as simple as you can get. People have tried paralleling in second packs with similar voltages and found very little benefit. As I understand it, a basic conversion pretty much needs the following:

1. A way to charge the external pack from the grid, otherwise you're still just charging it off the gas engine and the improvement is small.

2. An external pack voltage high enough (~240V) to cause the OEM battery BMS to go into a recalibration routine and increase its estimated SOC (called SOC drift). Othewise, the BMS will ignore whatever current you are putting into the OEM battery and act like the other battery isn't even there. This will also cause the improvement to be very small. In the mean time you could actually damage the OEM battery, as you are putting charge into it that the BMS doesn't acknowledge which could lead to an overcharge condition.

3. A way to monitor the state of the OEM battery and connect and disconnect the external battery as needed. This pretty much means being able to read the CAN network traffic, and control a couple of big relays or a big (and expensive) DC to DC converter. By continually pulling the OEM battery SOC up to a pretty high level, the cars HV controller reacts by trying to use more power from the electric motor to bring the SOC back down. This is where the real benefit comes from. The conditions under which the packs need to be connected and disconnected have to be done quickly and precisely to keep the car happy and using all that extra power, so you really need some sort of computer keeping on top of it. This can be a CAN-View, or a dedicated controller like the one Chris is working on.

Rob

 

dont you mean 240 DC? and not ~


i am looking at the following

12 volt battery DC 12 to AC ( blocksinus ) 230volts~ and then a AC-DC converter so i get 230volts DC
I then make a relay that only works when the car is running and then switch the DC to the main 201,6 volts DC lines of the car.

Charge is nog going into the battery but used directly without using battery capacitie so it stays full.

when you stop the car the relay switch the dc converter OFF again.

charge to the 12 volt batterie can be done by solar panel @home or even on the car roof!

 

He means approximately 240vdc... that's what the tilde (~) symbol means in normal usage.

What kind of losses are you going to incur with all that converting? That's a lot of heat generated, then there is the weight of the converters. How many 12v batteries in parallel do you plan on using and what's the weight going to be?

Cheap!, I can't thank you enough for this thread. It has taken me three days to read through it all, but I am looking forward to doing a conversion of my '08 Prius sometime in the future (money permitting).

I am interested in the box vs. cage battery containment discussion-- is the box decision based upon ventilation considerations?

 

yes
maybe the 20 battery parallel is the more smart way to go
but i wanna do it the cheap way

20 lead battery's used @ 12Ah mean 240Ah
then i need to buy the really expensive lead battery there has really gone up in price because of the lead demand.

when i use a 250Ah gell battery ( less expensive )
and a 800 dollar 2500watt DC to AC converter ( modified sinus )

then i can make a AC to DC converting device to work with a price of Les then 160 dollar.

thats wy i want to go for this i think cheaper way

 

Instead of running the Batteries in parallel why don't we do the following.

1) Install an EV switch. Run in EV mode until the original existing battery runs so low that the ICE turns on to charge the battery. Do not let it charge the battery.

2) Break connection with the existing battery - reconnect to the spare battery. (would need some kind of circuitry to do this automatically). The ICE should shut off as now you have a full battery again to run in EV mode.

3) When you run out of battery power on the second battery pack, then switch back to the first pack and run ICE to charge up and use your Prius to get home.

4) At home use the house charger system to charge up with cheap MIDNIGHT electricity. Charge both batteries until full.

5) Get more spare battery packs (test a few junkyard Prius batteries) and load up the Prius to the GVW limit after pulling out spare seats, and spare tire (use a STOP LEAK - FIX A FLAT).