elk trg1640 vs honeywell hpt1640

[mikefamig]

I ordered an Elk trg1640 transformer to power a p212s and received a Honeywell hpt1640.
 
The best I can tell, the Elk is a 45va supply and the Honeywell 40va and the Elk calls itself a resettable fuse device and I can't tell if the Honeywell is fused or not. They are both class two transformers but that tells me nothing.
 
You might say that I'm suffering over nothing and I can't imagine that the 5va difference in power will be a problem but every time I overlook a detail it comes back to bite me in the ass. Other than the fact that the Elk part costs a couple of dollars more than the one I received do you think I should care? I can't imagine that it will make any difference but would like to hear if anyone has had experience with the htpt1640 as a replacement.
 
Mike.

 

[sda]

I'd be pizzed because I didn't get what I ordered, unless of course it was something better, which in this case it isn't.
 
Then again, make sure you didn't buy something that was described as "ELK 1640 equivalent", because then you got what you got.

 

[mikefamig]

I'd be pizzed because I didn't get what I ordered, unless of course it was something better, which in this case it isn't.
 
Then again, make sure you didn't buy something that was described as "ELK 1640 equivalent", because then you got what you got.

 
 
I'm more concerned on whether or not it is equivalent.
 
Mike.

 

[drvnbysound]

Doesn't sound equivalent to me.

 

[mikefamig]

Doesn't sound equivalent to me.

True but if you were doing an install would you feel confident to use it to supply an elk p212s?
 
Mike.

 

[jpmargis]

Do the $%#! math!  Two amps @ 12 volts is 24 VA.  Assuming a conservative converter efficiency of 75 percent, brings the total worst case load to 32 VA.  A 40 VA rating is more than adequate.

 

[RAL]

A little back of the envelope calculation might help....
 
The P212S can put out 2A at about 13.8V.    That's a total of 27.6 VA for the load it powers.  Plus, it needs to be able to charge the battery, which can be up to a 12Ah battery.   Assuming the battery is discharged, a typical charging rate would be C/10, or 1.2A.    So, 1.2A x 13.8V, or 16.6 VA.    27.6 + 16.6 gives you a total requirement of 44.2 VA.
 
I would say that a 40 VA transformer is close, but not quite good enough.  It would do fine most of the time when the battery is fully charged and just needs a float charge to keep it topped up.  But when the battery is discharged, it would struggle to carry the combined load.
 
This calculation ignores the typical inefficiency of the power supply regulator circuit, so all the more reason to go with a 45 VA transformer rather than the 40 VA.

 

[mikefamig]

You guys are talking about the p212s 12 volt output. The 40va that I quoted is the 16.5 volt output of the transformer.

 

[RAL]

You guys are talking about the p212s 12 volt output. The 40va that I quoted is the 16.5 volt output of the transformer.

 
Yes, but the power supply transformer has to provide an equivalent number of VAs to the input of the power supply to cover the load on the output side, plus any losses due to power supply inefficiency.
 
My simple calculation above showed that you need almost the full 45 VA on the output side or the power supply that the transformer provides to the input side, without any inefficiency loss.   In reality, there are losses, but my calculation was pretty rough.   But good enough to convince me that a 40 VA transformer would be marginal.

 

[mikefamig]

Thank you all for the help. I'm not an electrician and this system is fairly complicated so I appreciate it. I sent off an email to the place that I bought the transformer requesting they send the Elk transformer.
 
A side note....I was just down in the garage where the p212s and the Honeywell transformer are installed and I the feint gurgling sound of gases escaping the battery. Is the p212s a fast charger? The battery is a brand new elk 18ah battery.
 
Mike.

 

[mikefamig]

Update.....I just powered the p212s off. It was outputting 15.5 volts on the battery terminals and about 14 volts on the 12v outputs. Something aint right.
 
Mike.

 

[mikefamig]

I think that I discovered why the output voltages were so high, I didn't RTFM well enough. I missed the part about setting the zone assigned to the p212s as power supervisory. I didn't even know that there was a zone assigned to the p212s. I learned through elkrp that it had been assigned zone 207 so I had to assign a new group of hardwired zones and assign 207 as power supervisory and now the voltages are stable around 13.9 volts.
 
All I can say is whew.....I just dodged a bullet.