I have recently had several battery short circuits that generated large amounts of gas and fumes! I have rebuilt My battery box and provided floor vents. I would like to provide forced air venting during charging and during discharge. Anyone have a suggestion for control of a blower during those cycles? John
During charging cycles?
Easiest would be to run the fan control from the ignition switch or battery charger input
(A/C). The below diagram assumes that you are charging your batteries from both a shore-power charger, and the main alternator. There are two relays, one is controlled by a DC coil that gets power from your ignition switch, the other relay is controlled by and AC coil that gets power from the shore-power cord. NOTE THE USE OF FUSES!!!
This is an electromechanical "OR" circuit - where the shore-power OR the ignition switch, turns on the fan.
-Tim
Edit: Whoops, just saw the "discharge" part - this could make it more complicated... If you have a habit of turning off the breakers to high-load devices while not in use, the simplest way to add "discharge cooling" is to add a few diodes to the below illusrated "IGN+" input to the DC relay, with the stripes on the diode pointing to the relay. One diode's non-striped lead would go to the ignition, another diode's non-striped lead would go to the SWITCHED side of the load's breaker (all of the striped sides should be connected together at the below illustrated "IGN+" input). The diode will prevent power from getting to the other circuits (the diode makes the wire a "one way road"). Theoretically you could add several diodes and run parallel controls to each high-load breaker to turn on the fan any time you run one of those loads. Also, if you have a high-power inverter, it may already have a fan control output which can be wired with another diode into the same DC circuit.
Of course, the most acurate way to control fans is when they are needed (battery temp gets too high). You would also want to start dumping loads and/or sound an alarm if you batteries are getting hot enough to out-gas (and probably turn off the charger if that is causing it). For that, a small temperature sensor, melted into the lead battery terminals will give you a good reading (one for each battery). This of course gets a bit more complicated. -T
Highly recommend you only use a marine approved bilge blower. A 150cfm should be enough. Since the gasses from a battery are very explosive, you need a blower that is completely shielded from spark-and that would be a marine bilge blower. Good Luck, TomC
Hmmm. What about using a ring shaped sensor wrapped around the battery's + cable. I am thinking about the something like the clamp that hand held amp meters use. This would sense current flowing into or out of the battery. Take the output from that into a power relay to drive the fan. That way the fan can be set to operate whenever a set level of amps are flowing into or out of the battery bank.
Thanks for the input,I was hoping someone would jump in with so and so makes a module for just that purpose! I am an electronics person but just have not come up with a simple method to get it done. I thought about some kind of current sensor like a shunt to drive a sensitive relay but just isn't clean enough for Me. I do not need another cloud of gas in the coach because a battery decides to conduct and boil and kill the other bats. The explosiion proof motor or ignition protected motor is noted. Thanks and I am still open to all thoughts. John
What you re looking for is a DC Current relay. I haven't done any research but I'm sure tey are out there. The old 4104 used one on the stop light circuit to light the dash telltales.
Can you provide a photo of the battery box? It help narrow down the questions of how to properly & safely vent the battery box.
Sojourn for Christ, Gerald
John,
You mention only floor vents? You should have vents both at the top and bottom of the battery box for good ventilation.
With these vents you really don't need forced air. An electric motor in the system just invites more explosion problems.
No need to make this complicated.
Gus,the battery box is in a closed bay. The vents are in the floor of the battery box which was part of the original custom coach conversion back in 72. I want to force air into the box so it vents out the floor vents outside of the coach. Previously it could only vent by gravity out the three floor vents. Not the best venting system. I will try to provide a picture if I can get My wife to post it for Me. My dilema is a method to turn on a blower which will force fresh air into the box when charging or discharging when gassing occurs. I want to avoid a blower switch so it is automatic and seamless. If I use a switch I will never remember to turn it off. Thanks for all the input I can use all the ideas. John
I'm afraid to admit that I'm having a bit of fun thinking about how I would design the circuit. I had a schematic mostly completed in my head. Then I realized that, once the current flow turned on the blower, the draw of the blower might be enough to never let the blower circuit turn off. I got a little chuckle off that one. Now I need to redesign with the tap-in for the blower upstream of the current sensor. :D
WEC, I have a relay that is activated by the gen light circuit which enables My vanner, so a easy way to have the blower on when being charged,read being maintained by the vanner. The next problem is I want to have the blower on when the heart is charging the bats when on shore power or on the gen set. Not to difficult, the hard part is when one or more of the bats decided to start pulling heavy current from the remaining bats and gassing like hell I also want the blower to come on and keep the grief to a minimum. Sort of difficult when having eight batteries in 4 series parallel sets. I thought about breakers but the 150 amp buss breakers have a 1/4" stud which does not seem adequate. All of the marine dc thermal breakers have the same puny studs. I am open to Your thoughts. John
John:
From the sound of your last post, it seems like we're going to need a bit more insight into what your wiring looks like. You mention you have 8 batteries in 4 series parallel sets. Are these 6 volt batteries yielding a 12 VDC house system? These can be charged by either your Vanner or Heart?
The other challenge sounds like you want protection in case the batteries start battling each other. Presumably this could happen even if there is no outside charging or draw is happening. Short of putting a sensor on each battery connection, I am not sure how to trigger the blower for that sort of event.
This is the type of device I was thinking about using to sense the current flow. It would wrap around the battery cable and trigger an output signal when the current reached an adjustable threshold.
http://www.rbeelectronics.com/cs880.htm
John,
My point is that you MUST have both inlets and outlets to vent anything.
In this case the vents must be at the top and at the bottom, or at least not all at the bottom. As close to the top as possible is best.
No matter how many you have at the bottom the rising charging gas will not vent out the bottom, especially Hydrogen which is explosive. It works its way naturally up into the bus, the reason you smell it. Even if you have a fan blowing into some of the bottom vents you still will not be venting all the gas trapped at the top.
Again, it will vent naturally if you have top and bottom vents because the rising gas will pull fresh air through the bottom vents. It will probably vent best when moving but even pretty well when parked.
As I understand it your main problem is getting those top vents to the outside without ruining the exterior bus looks. If you can route the top vents into a wheel well it should work fine as long as the openings are shielded from mud and water. Through the compartment side is best if you can disguise the vents somehow and keep the sides looking good.
We aren't talking a huge amount of gas here unless you have a really big battery pack. However, if you have a badly failing battery it could produce a lot of gas, but not under normal charging.
I urge you not to make this thing overly complicated unless you just love gadgets and have no other bus projects that need attention.
What you are looking for is at http://www.backwoodssolar.com/catalog/images/batter1.jpg
Woops, thats only the JPG of it. Just go to backwoodssolar.com and look in the battery section.
Ed
About venting battery box with fan or blower...always apply fresh air into top-side or top of box with exhaust vent thorough the open bottom. Hydrogen gas is explosive when ignited via spark from electro static of the open brush type electric motor.
About a power tap source to automatically turn on fan whenever generator is charging...is to tap on the Relay terminal at the generator. You only want the fan running whenever it making hydrogen gas.
About a charger to energize the fan...I would call the charger's manufacture support and ask for information where to tap in to control fan's relay
Sojourn for Christ, Gerald
Blowing and not sucking is the key. Hydrogen goes up, which means it most likely will not hang around the bottom of the battery compartment. Perhaps a dedicated small muffin fan located in the forward bottom of the battery box will work.
The forward section because it will get help from the Bus Conversion going down the road. Bottom because the gas will go up. An outlet in the aft upper portion of the box will work for same reasons. Wire it thru your inverter/charger. HB of CJ
As HB says, vent Hydrogen from bottom to top. Trying to vent it out the bottom is like pushing on a rope.
It is much lighter than air, the very reason it was used in dirigibles.
Unfortunately, it is also very explosive - the reason it was stopped being used in dirigibles!!
Lot of over thinking here...
Temp sensor in battery box to start fan and shut off when done.
Charging makes heat. Shorts make heat.. DUH...
Depending on construction of the battery enclosure, some consideration as to whether the unwanted gases will be pushed out cracks, or otherwise accidentally directed to unintended areas by pressurizing the cavity...
Maybe best to run the fan as an exhaust, not as a supply?
happy coaching!
buswarrior
Quote from: DrDave-Reloaded on February 06, 2009, 02:55:29 PM
Temp sensor in battery box to start fan and shut off when done.
Charging makes heat. Shorts make heat.. DUH...
This was mentioned at the end of my first reply yesterday:
Quote from: Tim Strommen on February 05, 2009, 12:42:57 PM
Of course, the most acurate way to control fans is when they are needed (battery temp gets too high). You would also want to start dumping loads and/or sound an alarm if you batteries are getting hot enough to out-gas (and probably turn off the charger if that is causing it). For that, a small temperature sensor, melted into the lead battery terminals will give you a good reading (one for each battery). This of course gets a bit more complicated. -T
If you have a little bit of a draft in the box (of course then reducing the likelyhood of an explosive gas build-up) - a box temp sensor might miss one hot battery, but having a sensor in direct contact with the plates (via the lead terminals attached to said plates), will give you a damn good reading ;D. With the right circuitry attached, you could even single out the battery without opening the box up.
But then again, he said "simple"...
Quote from: buswarrior on February 06, 2009, 03:03:38 PM
...some consideration as to whether the unwanted gases will be pushed out cracks, or otherwise accidentally directed to unintended areas by pressurizing the cavity...
...Maybe best to run the fan as an exhaust, not as a supply...
I second this - and even with bottom outlets/vents, a duct that goes to the high-point in the battery box and has a fan on the other end that sucks out the fumes is a good way to go. Assuming that the fan is ignition-source free (since you will then be handling a dangerous gas mix...). Cheap brushless computer fans are good enough for this (no brush = no spark, and did I mention "Cheap"?).
-Tim
Quote from: DrDave-Reloaded on February 06, 2009, 02:55:29 PM
Lot of over thinking here...
Temp sensor in battery box to start fan and shut off when done.
Charging makes heat. Shorts make heat.. DUH...
I understand what you are saying, but my understanding is that his battery box is the entire compartment that houses eight batteries (big volume). If the bus is parked in the July sun, the box ambient temp could easily hit 95-100F, with nothing running and no need for the blower.
In February, with an outside temp of 20F, he could be charging or having a failure with outgassing like crazy, and the box temp may not hit 70F. (At least not until the explosion)
So at what temp do you set the thermal sensor to activate?
It is a simple high school physics that a fluid (air) will rise when heated (or pressurized) and will escape through the path of least resistance. So, it will not seek cracks if there is a large vent at the top. This is not to say that it won't find its way into cracks once it is outside the compartment.
This is all about relative temps and gas weights, not ambient or generated temps.
Blowing into a compartment with explosive gases is always safer than sucking it out. Sucking it through an electric motor (even if exp proof) because there can always be a spark from any electric or metal hitting metal source.
The over thinking here is trying to make it power instead of natural circulation. No matter what the temp there will always be natural circulation when there is air being heated, Hydrogen being generated or the bus moving.
Large battery volume means using large intake and exhaust vents.