Power source for Varrox - have I bought a pig-in-a-poke?

[Amari]

Grateful for advice from the electrically gifted.
I have just bought a Varrox for administering oxalic acid to my hives. To power it I have bought from Amazon an HQ 12v 7.2Ah sealed lead-acid battery. (sorry, can't work out how to add the link but see below). The Varrox has an output of 150Watts and the blurb advises a 'car battery 12v, 12amp, 40Ah'. Because I have only nine hives I reckoned that I don't need 40Ah (9x 2.5 minutes = 22.5 minutes).
The battery has arrived and seems so small. I am wondering if I've been a cheapskate - it cost only £14.99.
Thanks
HQ 12V 7.2Ah Universal Sealed Rechargeable Lead Acid Battery
by HQ
37 customer reviews | 10 answered questions
Price: £14.99 Free Delivery for Prime Members
In stock.
Dispatched from and sold by Amazon. Gift-wrap available.
13 new from £13.42
Lead acid battery universal
Voltage: 12 V
Capacity: 7.2 Ah
Dimensions: 151 mm x 65 mm x 95 mm

 

[drex]

Your figures are 150 watts, dave cushman says 12 V at 12 amp which is 144, so no great difference. You battery says it it produces 7 amps for an hour. It may be able to push out 12 amps, but you will need to charge more often, as it will be dead in about 30 mins. No electrician mind you.

 

[Apple]

Get a 40 Ah from your car scrappie chappie for a fiver

Ask for one that has a bit of life left in it
Now the expensive bit
buy an Oxford ???? regulated battery charger that will sequentially charge you battery, and can in fact recover a seemingly dead one, you can leave these chargers connected so that you always have a fully charged battery to use.
The current draw of the Varrox Vaporiser ( now the ONLY RECOMMENDED way to apply OA ) on the 7Ah gel battery will kill it dead in no time.



James

 

[Amari]

Get a 40 Ah from your car scrappie chappie for a fiver
Ask for one that has a bit of life left in it
Now the expensive bit
buy an Oxford ???? regulated battery charger that will sequentially charge you battery, and can in fact recover a seemingly dead one, you can leave these chargers connected so that you always have a fully charged battery to use.
The current draw of the Varrox Vaporiser ( now the ONLY RECOMMENDED way to apply OA ) on the 7Ah gel battery will kill it dead in no time.

James

Oh dear. Roast pork!

 

[MikeT]

The 7amp battery is far too small. My wife had a small wheelchair with 2 7 amp batteries and they would be flat by lunch time. Also consider once the battery is below 12 volts you will not get the same amps as when it is fully charged therefore the Ox acid vapouriser may not get hot enough

Buy a 40 amp leisure battery, car batteries will not stand constant discharge and recharging.

Can you get near your hives with your vehicle? If you can run a lead from the car battery, this should be the same thickness as the lead attached to the unit, also remember there will be a voltage drop if the extension lead is too long, max length 7m.
keep the car running so you do not discharge the battery.

 

[oliver90owner]

The replies above are about spot on.

The simple facts are there for the finding (re lead acid batteries) on the net.

Where 'C' is the capacity of the battery, it is often the total stored power if dischared at C/20.

At nearer the 2C discharge rate, the capacity is likely only about 5 Ah, if that.

Secondly, discharging to more than 20% DoD (depth of discharge) will likely considerably shorten the expected life of the battery. Also full charge must be returned without delay, if the capacity is not to be lost.

Lead acid batteries have a reaonably low internal resistance, but modern batteries are designed and rated for minimum cost for a given capacity.

Your varrox would consume 22.5kJ over a period of 150s at 150W. It would be suffient for one hive easily, two adequately. Any more would likely be stressing the battery which could fail early and be practically exhausted.

Given time to recover, you might get 5 hives done before the battery voltage would drop too far to be properly effective for the required power delivery. But that would not be a good way to preserve your investment.

On the charging side, a sealed battery cannot be reharged too quickly if it is expected to last. Usually a maximum of 14.4V is permitted for float charge and the current may well be limited for such a small battery.

50 years ago, or more, flooded lead acid batteries were made with far greater plate areas and were capable of repeated charge and discharge cycles - cars were left with lights on all night if parked on the road! Dynamos did not recharge anywhere near the rates that the modern alternator pushes out. Most of this type of automotive battery had disappeared by the early 1970s. It is now very difficult to find a flooded lead acid battery for automotive applications in the car sizes.

Energy storage is one thing, delivery is another. Batteries capable of sustained (for a specified number of cycles) 80% DoD are available, but the cost is prohibitive, weight is considerable and applications are fairly specific - fork truck power packs and off-gridders are a couple, back-up for marine use is another area where reliable storage and high power release is required.

Treat one (or possibly two) hive(s) per day, recharge over the intervening hours and expect your battery to last a while - not sure how long, to be honest!

 

[Amari]

Many thanks for all the above answers, especially as they all agree - unusual for this forum. I should have posted before purchase. Good idea MikeT to park my motor next to the hives with a 7m lead, I think that will be possible, if not I can adjust the position of the hives slightly. Presumably 7m jump leads , if available, would suffice? Being electrically naive it amazes me that I need this capacity battery, which would be OK for a vehicle starter motor, to heat a metal spoon for 2.5 minutes.

 

[Amari]

I see that Amazon sell a 6m jump lead "800amp, heavy duty OK for trucks"
Bless them, I can return the battery and charger I ordered, collected and with full refund.

 

[Amari]

The 7amp battery is far too small. My wife had a small wheelchair with 2 7 amp batteries and they would be flat by lunch time. Also consider once the battery is below 12 volts you will not get the same amps as when it is fully charged therefore the Ox acid vapouriser may not get hot enough
Buy a 40 amp leisure battery, car batteries will not stand constant discharge and recharging.
Can you get near your hives with your vehicle? If you can run a lead from the car battery, this should be the same thickness as the lead attached to the unit, also remember there will be a voltage drop if the extension lead is too long, max length 7m.
keep the car running so you do not discharge the battery.

Progress report: I bought a heavy duty 6m 'truck' jump lead from Amazon. Today I tested the kit attached to my car battery. First the Varrox with its 3m lead, then with that 3m plus 6m jump leads = 9m. Both gave a most satisfactory burn (copious smoke blown away from me across a field). I'll apply to my hives as soon as the temp (hopefully) rises to 8C.

 

[Erichalfbee]

I drove the car across the field to the back of the hives.....no extension needed. Hooray. As five of the hives are poly I am just waiting for a solder mat to put on the OMF under the varrox and I'm all set

 

[MikeT]

"Progress report: I bought a heavy duty 6m 'truck' jump lead from Amazon. Today I tested the kit attached to my car battery. First the Varrox with its 3m lead, then with that 3m plus 6m jump leads = 9m. Both gave a most satisfactory burn (copious smoke blown away from me across a field). I'll apply to my hives as soon as the temp (hopefully) rises to 8C"

Glad everything worked out OK, and pleased we saved you some money.

Mike

 

[oliver90owner]

I'll apply to my hives as soon as the temp (hopefully) rises to 8C.

What is so magical about 8C? The internal hive temperature will soon rise with an input of 150J/s. Bees would still be well clustered at 8C anyway and the internal hive temp will likely be above ambient (definitely, above the cluster).

I never bothered to take a thermometer with me. Not done in freezing conditions, but I would expect about 5C is as good as 8C. Common sense rather than rocket science level is all that is needed. An extra 20s on time would warm it more. Remember, steam at 100C is going to be coming off the varrox before sublimation begins, some seconds later (assuming you are using the hydrate form of oxalic).

 

[Amari]

Hivemaker suggests bee cluster should not be too tight

 

[Amari]

"Progress report: I bought a heavy duty 6m 'truck' jump lead from Amazon. Today I tested the kit attached to my car battery. First the Varrox with its 3m lead, then with that 3m plus 6m jump leads = 9m. Both gave a most satisfactory burn (copious smoke blown away from me across a field). I'll apply to my hives as soon as the temp (hopefully) rises to 8C"

Glad everything worked out OK, and pleased we saved you some money.
Mike

Yes, thanks for your earlier suggestion Mike.

 

[Arfermo]

Hivemaker suggests bee cluster should not be too tight

They will soon loosen up with the varrox under them.

 

[Little John]

Ampere-Hour ? Frequently misunderstood (not unreasonably) when considering car batteries. A 40Ah battery will produce something like 20Ah of useful energy, after that it will need re-charging. Not claiming that this is 'accurate' - just something to be born in mind.

There's another aspect of batteries which is relevant here - the battery's internal resistance. Large capacity batteries have a very low internal resistance, which allows them to deliver large currents without significant voltage drop - this is commonly referred to as their 'cranking amp rating': i.e. that current which can be supplied to a starter motor under load.

A small capacity battery (which do not have 'cranking amp ratings' as they are unsuitable for cranking car engines) will have a small plate area, and thus a higher internal resistance than a larger capacity battery - so - when fed into a significant load, the battery's internal resistance will cause a drop in voltage, which in turn causes a reduction in current - so that a reduced amount of power reaches the load, which may be inadequate for it to operate (depending on what the load is, of course).

LJ

 

[Erichalfbee]

I'm glad I can get the car down to the hives

 

[Little John]

I'm glad I can get the car down to the hives

... and just think of the money you're saving on wheel-barrows !

 

[Amari]

Ampere-Hour ? Frequently misunderstood (not unreasonably) when considering car batteries. A 40Ah battery will produce something like 20Ah of useful energy, after that it will need re-charging. Not claiming that this is 'accurate' - just something to be born in mind.

There's another aspect of batteries which is relevant here - the battery's internal resistance. Large capacity batteries have a very low internal resistance, which allows them to deliver large currents without significant voltage drop - this is commonly referred to as their 'cranking amp rating': i.e. that current which can be supplied to a starter motor under load.

A small capacity battery (which do not have 'cranking amp ratings' as they are unsuitable for cranking car engines) will have a small plate area, and thus a higher internal resistance than a larger capacity battery - so - when fed into a significant load, the battery's internal resistance will cause a drop in voltage, which in turn causes a reduction in current - so that a reduced amount of power reaches the load, which may be inadequate for it to operate (depending on what the load is, of course).
LJ

So are you able to tell me how many times I can fire the 1500 Watt Varrox for 2.5 minutes without depleting my standard saloon-car battery? Admittedly in my apiary I can leave the engine running but I have volunteered to treat a neighbouring apiary where I'll have to park in the road and lead the cable through the hedge and would prefer not to leave the engine running. Another apiary plans to port a boat battery. Thanks.

 

[oliver90owner]

150W, 12V, amps equals watts divided by volts. So current is around 12A for 2 1/2 minutes. Car batterries are around 45Ah (smaller petrol engines). Work it out from there?

Another way of looking at it is: would your battery be seriously depleted if you left the headlights on for 3 minutes? If not, it will do one sublimation at least.

your varrox is not 1500W. I can assure you of that.