Roadpro 12v Hairdryer - is Allan about?

[arthur49]

2 x 110Ah batteries with cigarette lighter type socket direct to batteries with heavy cabling to prevent voltage drop. (Anybody know of a better plug and socket capable of higher amps ?)

Roadpro 12v Haidryer rated at 180w

 

These hairdryers are not very good - my wife tells me! - and I understand that, but the power cable gets warm when in use. That warmth is obviously wasted energy not getting to the dryer element. (I cannot see an easy way to upgrade the cabling)

 

Now I would have thought the dryer was designed to carry full 15A without cable heating up, but could it be voltage drop at the battery, under haidryer load? In other words when dryer is switched on the voltage at battery drops a little, physics then dictating that current rises? Maybe starting the engine whilst dryer is in use would stop the assumed voltage drop?

 

(She also has a 400w 240v hairdyer. Maybe better fitting a 600w modified sine wave inverter for this dryer and bin the Roadpro. But that would blow the x5 Rule of battery/inverter? Don't ask about the 2000w 'megablaster' which is only used when on EHU within one mile of a power station 8-) )

[colin]

Buy her a pretty towel for next birthday, you know you can't go wrong with something practical. :D

[aandncaravan]

Arthur, At 12v the element/Motor does draw 15A.

At 14.4v the Element/Motor draws just 12.5amps, so the voltage of the battery will have quite an impact. Especially if dropping near to 11v under load?

 

One of the advantages of a Varta Powerframe battery is that the resting voltage is higher than conventional batteries, resulting in a better delivery of power. The 70% claimed improved current flow, through reduced corrosion and greater electrical efficiency, also results in reduced voltage drop. Especially under load.

 

Exactly why, we say, there isn't a better battery for the high current drawn by Diesel heaters, or other high current appliances. For example most Inverters will be more efficient on a Varta Powerframe battery bank than Lucas.

 

 

However, I am sure you don't want to change your batteries to resolve a Hairdryer issue, so running the engine should have quite a beneficial effect?

 

 

Also consider that while the element and Motor in the Hair dryer is drawing 180watts, the 'power rating' does not take account of any 'consumption' by poor connections/switches.

 

If the Switch was poor quality, for example, the actual draw from the battery might be greater, even though the Element/Motor would still be 180watts.

 

I get my Wife to drive and I stick my Head out of the window to dry my Hair, could maybe your Wife try that?

:-D

 

The average efficiencey Inverter coping with a 400w load is likely to draw around 45amps'ish from the battery, but that is offset by it being drawn for a shorter time than the 180w Clockwork one.

 

45amps split across two wet acid batteries for 10 minutes should not overload them unduly, you are only over the 20 amps per 100Ah guideline by 2.25amps per battery.

 

 

[arthur49]

aandncaravan - 2017-06-15 1:53 PM

 

I get my Wife to drive and I stick my Head out of the window to dry my Hair, could maybe your Wife try that?

:-D

 

Thank you Allan ...... you can tell my wife your suggestion if you're brave enough 8-) 8-) 8-)

 

Re my hair. What hair? I insist its not baldness its a solar panel for a sex machine .... with a Votronic MPPT controller of course :-D :-D :-D

[Charles]

"Now I would have thought the dryer was designed to carry full 15A without cable heating up"

 

You would have been right 50 years ago. Now everything is made as cheaply as possible. The cable gets warm because it's too thin and has a voltage drop across it. Say the volts drop across it is 2v... 2v x 15a = 30w... your flex would be consuming 30 watts!

 

 

[Charles]

RE the battery voltage drop... to know what wattage the element is at different voltages, you need to know it's resistance, it's not always an 180w element.

 

It you do the sums:

 

I = V/R to find the current through the element at the batteries particular voltage.

 

Then

 

P = V x I to find the elements Power consumption at that current.

 

What it tells is if you lower the voltage to an element it uses less power.

 

P = Power in watts

I = Current in amps

V = Voltage in, you guessed it, volts

R = Resistance in ohms

 

 

[veletron]

Hi

 

There is no regulation with these hairdryers, so the higher the voltage, the higher the power. The current through the hairdryer is down to the resistance and voltage applied.

 

Given the specified nominal 180W @ 12V we can assume resistance of 0.8Ohms - this figure, 0.8Ohms is the only thing that can be considered static in a MH - the voltage is rarely exactly 12V!

 

At 14.4V, the current will be (14.4/0.8) = 18A, and the power will be (14.4x18) = 260W

 

From the above it is evident that at higher voltages, more current is drawn and thus more power created, while at lower voltages, less current is drawn, and let power developed. As the element heats, the resistance also lowers, increasing the power further. Voltage drops along the cabling will tend to reduce the real wattage of the drier. The limit will be where the element burns out or the fuse blows!

 

I have the same hair drier. I chopped off the cigar lighter socket and replaced it with a Hella plug and fitted a Hella socket fused and close to the leisure battery with decent cable. Hella plugs/sockets are far better for high current applications than the standard cigar lighter socket. Little can be done about the cable on the drier apart from keeping running times short, and not using it when the hookup is connected (thus reducing the current).

 

The inverter-driven 400W hairdrier will be far far more effective. Suggest doing what I have done and fitting the inverter close to the batteries, and back wiring it to all the sockets in the van via a DPDT changeover relay with mains coil, where the coil is energised by the EHU input. I rarely hookup, but always have mains available at all sockets in the van. The cost being under £150 DIYed (with cheap 1KW modified sine inverter)

 

https://www.amazon.co.uk/HELLA-CONTINENTAL-DC-ACCESSORY-PLUG/dp/B0011IATW4/ref=sr_1_3?s=electronics&ie=UTF8&qid=1497607354&sr=1-3&keywords=hella+plug

 

Nigel

[arthur49]

veletron - 2017-06-16 11:06 AM

 

Given the specified nominal 180W @ 12V we can assume resistance of 0.8Ohms - this figure, 0.8Ohms is the only thing that can be considered static in a MH - the voltage is rarely exactly 12V!

 

At 14.4V, the current will be (14.4/0.8) = 18A, and the power will be (14.4x18) = 260W

 

The inverter-driven 400W hairdrier will be far far more effective. Suggest doing what I have done and fitting the inverter close to the batteries, and back wiring it to all the sockets in the van via a DPDT changeover relay with mains coil, where the coil is energised by the EHU input. I rarely hookup, but always have mains available at all sockets in the van. The cost being under £150 DIYed (with cheap 1KW modified sine inverter)

 

 

Thank you Nigel thats really interesting. So using your formula above at battery voltage without engine running of say 12.6v then the power will be = 200W (12.6/0.8x12.6).

So increasing power by running the engine - we have a B2B - will lift voltage at battery to 14.4v and thereby power at dryer to 260W - thats a big increase albeit its still pretty weak.

And I like the inverter idea but I believe there is a x5 'rule' http://www.aandncaravanservices.co.uk/inverters.php which means my 2x90Ah batteries might struggle. But then again if I can get 2 years service out of the batteries to keep my wife more content, then its a price worth paying!

[Charles]

You're welcome

[bobalobs]

A few years ago we were told that Eberspacher marketed a hairdryer to attach to the hot air vent of their diesel heaters. Sales were good and it was then found that lorry drivers were putting the hairdryers down their sleeping bags to warm them up before going to bed!

[veletron]

I run a 750W 240V electric kettle off my inverter with 2x140AH batteries - yes, it does stress the batteries, and I suspect I will be replacing them after 3 years. They are currently 18 months old. So long as you limit the power to say 400W, it will likely be fine - you would have to accept a reduced service life on the batteries though.

[arthur49]

veletron - 2017-06-16 11:00 PM

 

I run a 750W 240V electric kettle off my inverter with 2x140AH batteries - yes, it does stress the batteries, and I suspect I will be replacing them after 3 years. They are currently 18 months old. So long as you limit the power to say 400W, it will likely be fine - you would have to accept a reduced service life on the batteries though.

 

Thanks Nigel

[arthur49]

I just had another thought on this. An inverter of say 600W will draw max of say 50A. Thats a huge draw on my 2 x 110Ah batteries and I accept if I go down this route I will shorten the life of my batteries.

 

BUT I have a B2B capable of 45A at 14.4v, so that would suggest if I started the engine before inverter was used with 400W hairdryer, then less deterioration to batteries as most of current coming from B2B? Or am I optimistic?

[veletron]

Would definitely help - but engine idling in the UK is an offence (apart from to defrost a windscreen, or while stuck in traffic, at lights etc).

 

One of my personal hates is motor homers idling an engine to charge a leisure battery. Illegal, and extremely inefficient - extended idling also not great for the engine! Better to equip the vehicle for the use to which it is put (extra leisure batteries, solar panels etc).

 

25A per battery is not an unreasonable amount to demand of the batteries over short periods - just make sure the batteries, inverter and B2B are connected with 25mm welding cable (or similar). This reduces voltage drops (eg wasted energy). Also, if runtime of the hairdrier is limited to 5 mins, and you move off (and hence recharge) the batteries shortly after, any reduction in service like will be minimal. You could also consider a solar panel (superb in summer, near useless in winter!).

 

I kept distances short, and wired everything with this: http://www.ebay.co.uk/itm/Welding-Cable-Battery-Live-230-Amp-25mm-Red-Flexible-Per-Meter-Mig-Arc-Welder-/401024360656?hash=item5d5eea20d0 using some solderable ring terminals: http://www.ebay.co.uk/itm/4-GAUGE-AWG-5-16-HOLE-AMP-AMPLIFIER-WIRING-RING-TERMINALS-RED-BLACK-POWER-CABLE-/400498266866?var=&hash=item9c0512d4e9

 

The B2B will need cable like this to get the best out of it - if you are using the pre-existing wiring for the B2B you might as well save your money.

 

Nigel

[veletron]

Lion Battery powered 400W hairdrier with 12V charger

 

- 7 mins runtime so it says.

 

£149 - Ouch!

 

Looks like it originates from China - usual rules apply - don't leave it charging when you are away!

 

https://www.amazon.co.uk/Cordless-Dryer-2-battery-FreeDryer-400Watts/dp/B06XQZKVXK/ref=sr_1_fkmr0_1_a_it?ie=UTF8&qid=1497820856&sr=8-1-fkmr0&keywords=400w+travel+hairdryer

 

Nigel

[arthur49]

Cheers Nigel. Cabling used for B2B etc is 25mm square

[Derek Uzzell]

veletron - 2017-06-18 10:17 PM

 

Would definitely help - but engine idling in the UK is an offence (apart from to defrost a windscreen, or while stuck in traffic, at lights etc).

 

One of my personal hates is motor homers idling an engine to charge a leisure battery. Illegal, and extremely inefficient - extended idling also not great for the engine! Better to equip the vehicle for the use to which it is put (extra leisure batteries, solar panels etc)...

 

Nigel

 

Surely motorcaravanners who choose to idle their stationary vehicle’s motor for long periods to charge a leisure battery will normally be doing this when the motorhome is parked ‘off road'? (On a campsite, in a field, etc.)

 

For a motoring offence to be committed, the motorhome would need to be stationary on a UK public road

 

https://www.confused.com/on-the-road/driving-law/stopped-parked-engine-running-idling-breaking-law-police-fine

[veletron]

Derek Uzzell - 2017-06-19 8:28 AM

Surely motorcaravanners who choose to idle their stationary vehicle’s motor for long periods to charge a leisure battery will normally be doing this when the motorhome is parked ‘off road'? (On a campsite, in a field, etc.)

 

For a motoring offence to be committed, the motorhome would need to be stationary on a UK public road

 

https://www.confused.com/on-the-road/driving-law/stopped-parked-engine-running-idling-breaking-law-police-fine

 

Point taken - not illegal off-road then - just an inconsiderate nuisance instead! ;-)

 

Nigel

[aandncaravan]

This thread has been referred to elsewhere so updating our reply.

There is not the issue with our figures as suggested as our example assumes that the Motor is drawing significant current in additional to the element, as is often the case with good lower power 12v hairdryers.

 

A powerful electric motor that is 'under voltage' will not only use more current but tend to overheat. A Motor given a higher voltage (within reason) will use less current.

 

Moving warm air faster is often more effective than moving hot air slowly, as demonstrated by toilet hand 'Air Dryers', like the Dyson Blade, hence the electric motor taking a significant chunk of the 'wattage' figures, if not the Lions share.

The one good 12v hair dryer we once had worked in this way. A high speed fan motor but lowish heat output. My Wife didn't like it, until she replaced it, only then finding out just how efficient it was for the wattage rating.

We swapped it for a high wattage 'more powerful' version that took more than twice as long to dry hair. It felt like it was working better, because the air felt warmer, but because the motor was so weak air flow was poor and drying time was extended enormously.

 

 

A Toilet hand 'Air dryer' with a good Motor will still dry your hands if the heater element burns out, but not if if's the other way around.

 

Note that our responses in our first post above are specifically aimed at efficient low wattage 12v hairdryers, not to higher wattage versions and especially not to Inverter driven 230v versions.

 

 

 

 

 

 

[Alanb]

aandncaravan - 2018-02-13 6:14 PM

 

 

.........A powerful electric motor that is 'under voltage' will not only use more current but tend to overheat. A Motor given a higher voltage (within reason) will use less current. .........

 

 

 

This is true for AC induction motors, like those powering a domestic fridge/ freezer, or those used in industry.

 

It is not true for small DC motors such as those under discussion.

 

 

Alan

[witzend]

bobalobs - 2017-06-16 8:46 PM

 

A few years ago we were told that Eberspacher marketed a hairdryer to attach to the hot air vent of their diesel heaters.!

A vacuum cleaner hose works off our Dometic blown air system

[Archiesgrandad]

The more of this thread that I read the more I wonder "why not buy a decent generator which will power a decent hair dryer and other useful things?" I had a 2.5 kw generator on my RV that didn't seem to upset anyone, and I had a 2 kw generator on my Sailor which was equally effective, so before the usual suspects launch into their anti-generator rant, why don't we try to encourage manufacturers to produce the quiet, economical generator we need. Where/s my tin hat?

 

AGD