measuring and switching HV battery voltage (hybrid)

ok here is the deal I would like to use a CC supply to equalize my cells in my aging hybrid battery, and I would also like to discharge the battery for reconditioning as well. the total pack outputs a voltage from 242V max to whatever I decide to drag it down to with the light-bulb(in my case 2x 200W, 100W or 25W standard household light-bulbs in series) discharge. Since the conditioning power supply I am using is a CC led power-supply with a 300V diode attached to ensure the psu is protected and it only kicks on above 135V that is the max I want to drag it down to. However I can’t let it be dragged down to that with 200W bulbs or even 100W ones (2x100W in series limit should be 185V then use 25W bulbs in series. ) so detecting the current flow would be advisable. Also I would like to switch the current in either flow direction with a FET because:
A. I would not like the connector hot unless the power supply is plugged in.
B. I would not like it to be able to charge without the 12V fan going
C. I would not like the discharge to be able to run down too far or even to quickly starting at a certain voltage level.

would like to use a nano supplied by the same 12V that powers the fan (this ensures it won’t be able to boil the batteries fan has to be powered for arduino to be, but catch is both power supplies (the CC HV DC one and the 12V wall wart) would share the same AC Line.
so I read here that common grounds can be a problem with voltage dividers , also any recommendations on the FET’s mind you I want to use them basically as relay’s either power supply or drain light bulbs connected to the battery.
Any hints on the design I would plug the nano into , also I would use some sort of voltage regulator from the 12V because I want to power an LED to readout the voltage and current currently flowing.
Any advice appreciated :slight_smile:
terramir

Nice plan but you might want to start with something simpler and work your way up to this.

In any case, I don't understand how you are planning to use a single CC power supply to equalize the hundreds of cells in your hybrid's battery.

I also don't understand why you "...like to switch the current in either flow direction with a FET..." when a relay would be easier.

(I assume that you are doing this out of necessity and don't care about any negation of your warranty.)

terramir: ok here is the deal I would like to use a CC supply to equalize my cells in my aging hybrid battery, and I would also like to discharge the battery for reconditioning as well. the total pack outputs a voltage from voltage level.

terramir

By hybrid battery what do you mean ?

Is this a car power unit , at 24 v i am a bit surprised.

What battery technology. ?

terramir: the total pack outputs a voltage from 242V

Very dangerous toy.

terramir: and I would also like to discharge the battery for reconditioning as well.

Most battery technologies don't like that. AFAIK only NiCad sometimes has to be discharged to counteract memory effects. Leo..

NiMH has memory effects(actually voltage depression) as well that become particularly prominant with hypercyclng that happens in hybrids SOC is kept around 60% max range 38% to 82% usually more like 45-50 to 65-70. Dangerous toy yeah 242 volts DC is very dangerous indeed most relays won't be able to hack it AC is much easier to switch, ssr's for dc in this range cost 100 bucks each and I would need two. but reallity is dc ssr relays are based on FET's and opto-couplers.

the only way to equalize 168 cells in 28 modules without individually charging the modules is to use a low current like under 1/10th C and make sure it's cooled properly.

a 350mAh CC PSU fits this bill perfectly. and the range of this supply is 143V to 286V (135v was incorrect oops) I have programmed reflow toasters and stuff, but determining voltage and current in something like this is new to me. hope this answers all the questions and comments a solution simular to this exists, however it wires the hv battery to a rubber covered plug that could be tampered with and it is live. I like to create a darwin proof solution, cause honestly I consider the harness dangerous as is, also there are no discharge limiting options nor any detection of airflow, if the cooling f onean ceases to work this would severly damage the battery using two thermistors one intake one somewhere in the battery casing will detect if cooling is actually working. or an airflow sensor. terramir

Hi, If you are going to equalize NiMH, you are better to disconnect them and treat them one cell at at time.

If you try cells in series, when you go through a discharge, any weak cells will discharge quicker, causing current flow problems and will eventually die, while trying to get the other cells down to a suitable discharge level.

This link may help. http://www.mpoweruk.com/balancing.htm

Individual cell monitoring is one of the criteria for multiple NiMH packs.

Tom.... :)

TomGeorge: Hi, If you are going to equalize NiMH, you are better to disconnect them and treat them one cell at at time.

If you try cells in series, when you go through a discharge, any weak cells will discharge quicker, causing current flow problems and will eventually die, while trying to get the other cells down to a suitable discharge level.

This link may help. http://www.mpoweruk.com/balancing.htm

Individual cell monitoring is one of the criteria for multiple NiMH packs.

Tom.... :)

these batteries are in modules of 6 cells and reverse charging during discharge at currents of 200 mAh (2x 25W light bulbs in series) is no big deal. these modules are designed to output 20 C currents and be intermittently charged at 17C currents 125A and 100A respectively.

The method I am talking about here has been well established these cells got oxygen recyclers that will allow for slight slow over charge as long as the hybrid battery fan is running it's only a 1/18.5C charge this has worked on prius 1st and 2nd gen , camry, as well as insight and others.

I just believe the wire harness is an accident waiting to happen, someone eventually will go poking around and will win the darwin award from what I gather 1500 of these chargers have prolonged the life of older high mileage hybrids and restored gas mileages that are closer to what these vehicles are capable of with new batteries, i.e like low 40 for the prius vs low 30's or less without the occasional treatment. a new battery could get the prius closer to original (high 40's maybe even more) but a new hybrid battery cost like almost 4000 with install. I understand voltage dividers, but the common ground problem of the 12 V and the CC supply as well as the hybrid battery during charge makes me look for solutions that will work and ensure that the plug is not live unless either the charging or discharging plug is in. all the rubber covered recessed contacts in the world will not compensate for stupidity in the long run. Honestly discharging is fairly safe at 25 W but I know some peeps will forget to monitor the voltages with the 100 W or 200 W eventually and the lower the temp the less resistance those light bulbs will have. So it's also about preventing costly screw-ups. any advice how to measure voltage and current safely as well as what low loss FET's I could use would be appriciated. terramir

vaj4088: I also don't understand why you "...like to switch the current in either flow direction with a FET..." when a relay would be easier.

(I assume that you are doing this out of necessity and don't care about any negation of your warranty.)

A relay that can handle 240 V DC is either in industrial contactor, or SSR in both cases they cost 100 bucks plus while two FET are in the order of two bucks each. As for the warranty if that wasn't expired I'd have a new traction battery. The only thing so really need a way to measure the voltage and current without running into common ground problems. terramir